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X-Objects: Movement and Visibility

Copy found at Wayback Machine.

All of the X-Objects have several methods for handling visibility and movement:

  • objSetLeft: set the left position of the element
  • objSetTop: set the top position of the element
  • objGetLeft: get the current left position of the element, if set
  • objGetTop: get the top position of the element, if set
  • objMoveRelative: move the object by a given horizontal and vertical change, relative to current position
  • objMoveAbsolute: move the object, absolutely, by given horizontal and vertical values
  • objHide: hide the object
  • objShow: show the object
  • objGetVisibility: show the object’s current visibility

The Navigator 4.x implementations of all of these interface methods is unique to this browser and version except for objMoveRelative and objMoveAbsolute, which are shared with the DOM and IE implementations.

The Navigator 4.x implementations of the movement and visibility methods are:

// hide element
function nsobjHide() {
	this.css2.visibility = "hidden";
}

// show element
function nsobjShow() {
	this.css2.visibility = "inherit";
}

// element's left position
function nsobjGetLeft() {
	return this.css2.left;
}

// element's top position
function nsobjGetTop () {
	return this.css2.top;
}

// set element's top position
function nsobjSetTop(top) {
	this.css2.top = top;
}

// set element's left position
function nsobjSetLeft(left) {
	this.css2.left = left;
}

 

As stated in the introduction, the IE-specific and the DOM objects (which Mozilla/Navigator 6.0 use) share much of the same interface implementations. The reason this can occur is because of a key shared concept between both browsers — all CSS properties are set through one specific object, the style object. Each HTML element has a property “style”, a reference to the Style object associated with that element and which contains all CSS settings for the element. Based on this, the implementations for movement and visibility for DOM-compatible browsers are:

// element's left position
function domGetLeft() {
      var lt = parseInt(this.css2.style.left);
	return lt;
}

// element's top position
function domGetTop () {
      var tp = parseInt(this.css2.style.top);
	return tp;
}

// set element's top position
function domSetTop (top) {
	this.css2.style.top = top + "px";
}

// set element's left position
function domSetLeft(left) {
	this.css2.style.left = left + "px";
}

// hide element
function domHide() {
   this.css2.style.visibility = "hidden";
}

// show element
function domShow() {
   this.css2.style.visibility = "visible";
}

The DOM compliant methods need to specify a unit of measurement as well as the numeric value for the new values. The X-Objects use pixels (px) for all of the DHTML effects.

The Navigator 4.x and the DOM-compatible browsers (IE and Mozilla/Navigator 6.0) share two method implementations, domMoveRelative and domMoveAbsolute, as these methods are higher-level implementations that call existing lower-level object methods to perform the actual movements:

// make absolute move
function domMoveAbsolute(newleft, newtop) {
   this.objSetLeft(newleft);
   this.objSetTop(newtop);
}

// move relative to current location
function domMoveRelative(left, top) {
   this.objSetLeft(left + this.objGetLeft());
   this.objSetTop(top + this.objGetTop());
}

By calling the exposed interface methods within the X-Object implementation, the correct version of the interface implementation is used for the movement. So, from Navigator 4.x, the left and top methods invoked when using objSetLeft and objSetTop are nsobjSetLeft and nsobjSetTop; from DOM-compatible browsers, the methods invoked are domSetLeft and domSetTop.

Now that we’ve provided the interface implementations for movement and visibility, let’s try them out.

Testing the implementations

I created an HTML page that contains a form with several buttons and a test block that is moved or hidden based on the user pushing the form buttons. The Body of the page contains the form and the test block:

<BODY onload="create_objects()">
<DIV style="position:absolute; left:10;
    top:10; background-color: yellow;
layer-background-color: yellow; padding-top: 20px;
width: 500; height:150; clip: rect(0,500,150,0)">
<form action="">
<center>
<INPUT type="button" value="Move Block Left"
        onclick="move_left()"> 
<INPUT type="button" value="Move Block right"
        onclick="move_right()"><p>
<INPUT type="button" value="Move Block Up"
        onclick="move_up()"> 
<INPUT type="button" value="Move Block Down"
        onclick="move_down()"><p>
<INPUT type="button" value="Hide Block"
        onclick="hide()"> 
<INPUT type="button" value="Show Block"
        onclick="show()"> 
<INPUT type="button" value="Show Visibility"
        onclick="get_visibility()">
</center>
</FORM>
</DIV>

<DIV id="info" style="position:absolute;
    left: 250; top: 180; width: 300;
height: 200;  background-color:red;
layer-background-color: red; clip: rect(0,300,200,0)">
<H1>Block with info</H1>
<p>
This is a block that contains two HTML elements:
        a header and a paragraph
</p>
</DIV>
</BODY>

Notice that the test block is positioned using absolute CSS positioning. This is necessary to access the DIV block with Navigator 4.x. Also, notice that the block has a reference to a CSS attribute, layer-background-color, that is not a valid CSS attribute. This is again necessary for Navigator 4.x in order for the background color to fit the block width and height, rather than just being background for the block contents.

Notice in the example that I’m not using units with the positional elements (i.e. using top: 180 instead of top: 180px) in the stylesheet settings. This was a bad habit I got into and one you shouldn’t get into.

You’ll find that this can cause problems with IE 6.0. You’ll also find that if you use standard mode with Mozilla (using a particular doctype of HTML strict or HTML transitional), that the examples won’t work at all.

Read more on Mozilla’s standard and “quirky” modes at Mozilla – reporting a bug.

The HTML page’s HEAD section contains the reference to the X-Objects script file and the DHTML code to implement the functions of the form buttons. These functions move the test block to the right or left, up or down, or show and hide the block. One last form button retrieves the current visibility setting for the block. The implementations of these functions are:

<SCRIPT src="cbobjects.js" language="javascript"
    type="text/javascript">
</SCRIPT>

<SCRIPT LANGUAGE = "JAVASCRIPT"
                   type="text/javascript">
<!--
// move element left
function move_left() {
   var lft = -10;
   theobjs["info"].objMoveRelative(lft,0);
}

// move element right
function move_right() {
   var lft = theobjs["info"].objGetLeft();
   lft += 10;
   theobjs["info"].objSetLeft(lft);

}

// move element up
function move_up() {
   var top = theobjs["info"].objGetTop();
   top+= -10;
   theobjs["info"].objSetTop(top);
}

// move element down
function move_down() {
   var top = theobjs["info"].objGetTop();
   top += 10;
   var lft = theobjs["info"].objGetLeft();
   theobjs["info"].objMoveAbsolute(lft,top);
}

// hide element
function hide() {
   theobjs["info"].objHide();
}

// show element
function show() {
   theobjs["info"].objShow();
}

function get_visibility() {
   alert(theobjs["info"].objGetVisibility());
}
//-->
</script>

You can access the Movement and Visibility testing page, using Internet Explorer 4.x and up, Navigator 4.x and up, and Mozilla.

I converted one of my existing DHTML pages to use the X-Objects. This page contains an Animated Menu using both the movement and visibility methods, and a timer to create the animation effect. Once you open the page, the menu animation starts. To see the code used, View source once the example is opened.

Another existing DHTML example is relatively simple, using hidden DIV blocks to create a “shadow” effect for Web page text. The example moved as is to the new X-Objects (as did the animated menu, above) without any modifications. Check out the Shadow Effect example, using View source once the example is opened to see the script.

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X-Objects: Creating the new X-Objects

Copy found on Wayback Machine.

The original cross-browser objects encapsulated browser-specific DHTML implementation behind a set of exposed interfaces, making it easier to change the implementation if needed, and easier to create and maintain my DHTML pages. When a new browser version (or browser) releases, I can make changes to handle the new implementation details in one place, the cross-browser object file, rather than within each page that uses DHTML.

So, instead of doing something similar to the following:

   if (navigator.appName == "Microsoft Internet Explorer") {
	document.all.div2.style.posLeft=incr;
	document.all.div1.style.posLeft=incr;
	}
   else {
	document.div2.left=incr;
	document.div1.left=incr;
	}

I can instead use:

   theobjs["div2"].objSetLeft(incr);
   theobjs["div1"].objSetLeft(incr);

If a browser changes its implementation, then all I need to do is modify the interface method, such as objSetLeft from the example, rather than have to modify the DHTML in each page where I set the element’s leftmost position using DHTML.

The cross-browser objects became cross-version when they provided support, with little modification, for the release of IE 5.x — a mark of a successful use of a technology. However, the true test for these beasties is the release of Mozilla/Netscape 6.0. We’ll find in this section, and the ones to come, that the cross-browser objects did require some modifications, though not to the existing interface methods. Instead, new methods have been added to handle new functionality, as well as changed functionality. Because of these changes, and the fact that the objects are now cross-browser, cross-version, and cross-DOM, I’ve renamed the objects to X-Objects.

We’ll take a look at how the X-Objects are created, and then in the following sections we’ll look at the browser-specific implementations of the X-Object interface, and examples using the new X-Objects.

X-Objects: object constructors

My old cross-browser objects are an array of DIV objects. I focused on DIV objects as both Netscape 4.x and IE 4.x supported pulling all CSS-positioned DIV blocks from a page. Additionally, I could create most DHTML effects just by manipulating DIV blocks. To maintain backwards-compatibility with Netscape 4.x, my new X-Objects are still pulling in absolutely positioned DIV blocks as DHTML objects. You’ll see later on in the examples that this still gives us considerable room to create our DHTML effects.

Every page that uses the X-objects to create DHTML includes an external Javascript file, pulled into the page using the following tag:

<SCRIPT src="cbobjects.js" type="text/javascript"
language="javascript">
</SCRIPT>

Additionally, the x-objects are created by calling a constructor method from this file: create_objects. The create_objects function tests to see what browser is accessing the page, and calls a browser-specific version of a DHTML object constructor function based on the browser. The X-Objects create_objects tests for the navigator name of “Microsoft Internet Explorer” and calls create_ie_objects if found. The code could be modified to test for version and call the function create_ie_objects function for IE 4.x, and create_dom_objects for 5.x and up. If the browser is Mozilla or Netscape, create_dom_objects is called if the version is newer; else the function create_ns_objects is called for Netscape Navigator 4.x:

function create_objects() {

    // Internet Explorer 4.x, 5.x, 6.x
    if (navigator.appName == "Microsoft Internet Explorer")
	   create_ie_objects();
    else // Navigator or Mozilla
        if (navigator.appName == "Mozilla" ||
                navigator.appName == "Netscape")
           if (navigator.appVersion.indexOf("4.") == -1)
	      create_dom_objects();
           else
  	      create_ns_objects();
}

The create_ns_objects method pulls the CSS positioned DIV blocks from the Layers collection and loads into an array, theobjs. This array is then accessed by the page creating the DHTML effect:

// For Navigator 4.x, pull all DIV blocks into object array
function create_ns_objects(newarray) {
   theobjs = new Array();
   for (i = 0; i < document.layers.length; i++){
     if (document.layers[i].name != "")
   	 theobjs[document.layers[i].name] =
            new ns_object(document.layers[i]);
     }
}

The create_dom_objects uses the getElementsByTagName method exposed with DOM Level 1, and pulls in all DIV blocks:

// For W3C DOM (Netscape 6.x, Mozilla), pull
// all named DIV blocks into an array
function create_dom_objects() {
  theelements = document.getElementsByTagName("DIV");
  theobjs = new Array();
  for (i = 0; i < theelements.length; i++) {
      var obj = theelements[i];
      if (obj.id != "")
         theobjs[obj.id] = new dom_object(obj);
      }
}

As you can see with both the Navigator and the DOM objects, only named DIV blocks are pulled into the DHTML object array.

The IE objects could also use the getElementsByTagName method, but I want the objects to be compatible with IE 4.x, which doesn’t support the DOM Level 1 release, so I’ll use Microsoft’s proprietary document.all collection to pull in the DIV elements:

// For IE, pull all DIV blocks into object array
function create_ie_objects() {
   theelements = document.all.tags("DIV");
   theobjs = new Array();
   for (i = 0; i < theelements.length; i++){
      if (theelements[i].id != "") {
	   theobjs[theelements[i].id] =
             new ie_object(theelements[i]);
	   }
      }
}

The DHTML array contains references to the X-objects created specifically for the browser. Each of these objects consists of the exact same interfaces, but pointing to different implementations of the functionality.

The Navigator object and it’s associated interface is:

// The Navigator DOM Object
//
//************************************************
function ns_object(obj) {
   this.css2 = obj;
   this.name = obj.name;
   this.objResizeBy = domResizeBy;
   this.objHide = nsobjHide;
   this.objShow = nsobjShow;
   this.objDisplay = nsobjDisplay;
   this.objGetLeft = nsobjGetLeft;
   this.objGetTop = nsobjGetTop;
   this.objSetTop = nsobjSetTop;
   this.objSetLeft = nsobjSetLeft;
   this.objMoveAbsolute = domMoveAbsolute;
   this.objMoveRelative = domMoveRelative;
   this.objGetWidth = nsobjGetWidth;
   this.objGetHeight = nsobjGetHeight;
   this.objSetHeight = nsobjSetHeight;
   this.objSetWidth = nsobjSetWidth;
   this.objSetZIndex = nsobjSetZIndex;
   this.objGetZIndex = nsobjGetZIndex;
   this.objSetClipRect = nsobjSetClipRect;
   this.objGetClipRect = nsobjGetClipRect;
   this.objGetClipLeft = nsobjGetClipLeft;
   this.objGetClipRight = nsobjGetClipRight;
   this.objGetClipTop = nsobjGetClipTop;
   this.objGetClipBottom = nsobjGetClipBottom;
   this.replace_html = nsreplace_html;
   this.objReplaceHTML = nsParamReplaceHTML;
   this.objReplaceText = nsReplaceText;
   this.objGetVisibility = nsVisibility;
}

If you’ve used my previous version of the cross-browser objects, you’ll see that the X-Object interface is the same as the cross-browser interface, with the addition of a few new interface methods. This highlights one very important point: the key to a successful use of object-based technology is never to remove or take away from an interface — new changes should result in growth not destruction.

The parameter to the object constructor is the actual browser-implemented object, which is then assigned to the X-Object’s css2 property. This property wrapping is necessary in order to be able to use the properties and methods supplied by the browser-specific object.

The dom_object and the ie_object point to the same method implementations for most of the exposed interface functionality:

// The W3C DOM Object
//
//****************************************************
function dom_object(obj) {
   this.css2 = obj;
   this.name = obj.id;
   this.objResizeBy = domResizeBy;
   this.objHide = domHide;
   this.objShow = domShow;
   this.objDisplay = domDisplay;
   this.objGetLeft = domGetLeft;
   this.objGetTop = domGetTop;
   this.objSetTop = domSetTop;
   this.objSetLeft = domSetLeft;
   this.objMoveAbsolute = domMoveAbsolute;
   this.objMoveRelative = domMoveRelative;
   this.objGetWidth = domGetWidth;
   this.objGetHeight = domGetHeight;
   this.objSetHeight = domSetHeight;
   this.objSetWidth = domSetWidth;
   this.objSetZIndex = domSetZIndex;
   this.objGetZIndex = domGetZIndex;
   this.objSetClipRect = domSetClipRect;
   this.objGetClipRect = domGetClipRect;
   this.objGetClipLeft = domGetClipLeft;
   this.objGetClipRight = domGetClipRight;
   this.objGetClipTop = domGetClipTop;
   this.objGetClipBottom = domGetClipBottom;
   this.replace_html = domReplaceHTML;
   this.objReplaceHTML = domParamReplaceHTML;
   this.objReplaceText = domReplaceText;
   this.objGetVisibility = domGetVisibility;
}


// The IE 4.x and 5.x DOM Object
//
//***************************************************
function ie_object(obj) {
   this.css2 = obj;
   this.name = obj.id;
   this.objResizeBy = domResizeBy;
   this.objHide = domHide;
   this.objShow = domShow;
   this.objDisplay = domDisplay;
   this.objGetLeft = domGetLeft;
   this.objGetTop = domGetTop;
   this.objSetTop = domSetTop;
   this.objSetLeft = domSetLeft;
   this.objMoveAbsolute = domMoveAbsolute;
   this.objMoveRelative = domMoveRelative;
   this.objGetWidth = domGetWidth;
   this.objGetHeight = domGetHeight;
   this.objSetHeight = domSetHeight;
   this.objSetWidth = domSetWidth;
   this.objSetZIndex = domSetZIndex;
   this.objGetZIndex = domGetZIndex;
   this.objSetClipRect = domSetClipRect;
   this.objGetClipRect = domGetClipRect;
   this.objGetClipLeft = domGetClipLeft;
   this.objGetClipRight = domGetClipRight;
   this.objGetClipTop = domGetClipTop;
   this.objGetClipBottom = domGetClipBottom;
   this.replace_html = domReplaceHTML;
   this.objReplaceHTML = ieParamReplaceHTML;
   this.objReplaceText = domReplaceText;
   this.objGetVisibility = domGetVisibility;
}

The main reason why I’m sharing implementations is that the functionality to make the DHTML effect is the same with a DOM-compliant browser as it is for IE — with some minor differences, that we’ll get to in later sections.

We’ll look at the implementation of these interface methods and test them out in the next pages.

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In celebration of technology

Recovered from the Wayback Machine.

It seems everywhere you look within the high tech industry, all you see is doom and gloom — closed companies, laid off employees, crashing Internet stock. I feel as if I should stand on top of a tall mountain, shouting out, “Is anyone still left in the technology industry!?!”

At the bottom of some of my emails I’ve posted the following:

Will the last person leaving the Internet, please turn off the router?

Have we all forgotten why we’re in this industry? Have we forgotten the joy and satisfaction over mastering a new technology, creating something from nothing? If you look around, you’ll see that not only is the high tech industry NOT dead — there’s an incredible wealth of wonderful new technology out there, most of it free or at least freely available. As poor as we are financially, now, we’ve never been richer when it comes to sheer capacity for technical advancement.

So, we’re heading into a recession. Well, in the last recession, back in the early 90’s, a gentleman named Tim Berners-Lee brought together some disparate technologies into this new thing called “the Web”. And he didn’t have the huge volume of “tech toys” to play with we do now.

Instead of looking back on what once was, we should be looking forward with eagar anticipation to what will be — the next great technical innovation, the next Web, the next revolution, the next reason why most of us entered this field for the first place.

Did I get a computer degree because I wanted to be rich and drive a BMW? When I got my degree in 1987, there weren’t many jobs in the computer field. Those that existed were, for the most part, already filled by old time engineers (no offense). There certainly wasn’t a web, though the Internet existed and was publicly accessible.

I ended up in this field because one day I sat down at an old green on black monitor and typed in a few commands in this language called “basic”, on this OS called Vax VMS, and the computer responded. I wasn’t a computer geek — I was studying law of all things. I only took the computer class because my logic teacher suggested I do so because I liked logic, and had a knack for it. However, when that computer responded, all bets were off, and I started my oddessey into, and my love, of technology that I continue to this day.

So, am I going to run away because we’ve hit another recession? No. No. Again, I say, No.

My current contract ends shortly and there are few contracts in San Francisco, at least until next year (end of the year is bad in the best of times). Rather than panic, I’m going to take this time to work with all these new technologies in a way I haven’t since I worked at Skyfish, my one and only foray into the world of dot coms.

(See article Death of a Dot Com at O’Reilly.)

Yes, I’m dipping into my reserves, and I may not find work next year, and may be out on the street (at least San Francisco has mild weather). Every time I receive a bill in the mail or pay my outrageous San Francisco rent, I am concerned.

BUT (big but here), I’m not going to throw my hands in to the air saying “Well, the dot coms have busted. It’s all over. I’m packing it in, and giving up”. I will not run because times are difficult; I will not give up because being in this field is no longer easy.

And I’m definitely not going to let some gutless wonder with a cult fixation on the other side of the world take away something that’s meant so much to me for so many years, as he’s taken away so much — including life — from so many others.

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COM+ to .NET: Fast Forward Your VB Components

Originally published at O’Reilly

The joke goes: “How do you pronounce ‘C#’?”, and the punch line is: “The language formerly known as Java.”

Extending this, you can say that .NET is “…the infrastructure formerly known as COM/DCOM.”

The .NET infrastructure is significantly different from COM/COM+. However, information about .NET has been out long enough so that most of you have passed the “But, why?” stage. You’re probably now interested in discovering how you can continue to create and support your existing component development to be ready when your organization adopts the production release of .NET. In particular, if you work with ASP and make use of COM+ components created with Visual Basic, you’ll be interested in how you can ensure that your components migrate well to the new .NET environment.

We’ll take a look at some of the changes .NET will have on your current VB ASP component development efforts. In particular, we’ll look at what you can do now to ensure your components are forward compatible with .NET.

What Variant?

One significant change between COM/COM+ and .NET is that the Variant data type is no longer supported; its functionality has been incorporated into the Objectdata type. For Visual Basic programmers this is a major change, particularly if you’ve worked with component development and have used variants to pass data to and from component methods.

For future compatibility, you can begin to use specific data types rather than the Variant in your new components. However, if you have used Variant in existing code, be aware that Microsoft has provided two means of porting your components that contain variants to .NET.

The first is the Visual Studio Upgrade Wizard, which is automatically engaged when you open your older VB code into Visual Studio .NET for the first time. This wizard replaces all instances of Variant with Object, and any time you try and type in a Variant, it replaces it immediately with Object. No additional effort is necessary on your part.

For instance, if you had a subroutine such as the following:

Sub test (ByVal varValue As Variant)

The upgrade wizard changes the subroutine to:

Sub test (ByVal varValue as Object)

If you didn’t provide a data type for a variable in VB 6.0, defaulting to a data type of Variant, the upgrade wizard automatically redefines the variable as Object in VB.NET.

(The upgrade wizard performs other upgrade modifications that will be highlighted throughout this article.)

You don’t have to open and convert a compiled component to .NET to ensure compatibility with the environment. A second means of porting your components to .NET is the utility, TlbImp. How to use this tool was discussed and demonstrated in a previous article; basically what happens is the tool creates a .NET assembly for the component that allows it to run within the .NET managed code environment, without having to recompile the component.

Dropping Variant isn’t the only change from VB 6.0 to .NET. VB Data Types and type checking is another significant area of change, which is discussed next.

Data Types and Data Typing

A chief concern about Visual Basic in the past, particularly from C++ or Java programmers, has been that Visual Basic is a weakly typed programming language. For instance, you can concatenate a number with a string in Visual Basic 6.0, and VB will automatically convert the numeric into a string value, using implicit conversion, as shown in the following example:

iValue = 123
StrSum = iValue & "123"

This type of operation is still allowed with .NET when using the overloaded concatenation operation (‘&’), as shown above, but any other use of numerical values where a string is expected will generate an error. As an example, you won’t be able to pass a number through a string parameter and have VB automatically perform the conversion:

Sub tstValue (String strValue As String)
...
Dim iValue As Integer
iValue = 13
tstValue iValue

The above works with VB 6.0, but it won’t work with VB.NET.

To support this new shift to stronger data typing, Visual Basic .NET also introduces the Option Strict statement:

Option Strict

Like its earlier predecessor, Option Explicit, Option Strict enforces explicit variable declaration:

Dim iValue As Integer

However, Option Strict enhances this data protection capability by prohibiting implicit conversions between strings and numbers, as well as limiting numeric conversions to those termed as widening conversions. A widening conversion is any that converts a smaller number, or less precise one, to a larger, more precise one, such as converting an integer to a double.

Option Strict also prohibits late-binding. Using this option, the following, while legal in Visual Basic 6.0 will generate a compiler error in .NET:

Dim obj As Object
...
obj.SomeMethodCall ...

As late-binding is detrimental to any wire based communication between application components, such as in a distributed or Web-based environment, you’ll want to avoid its use even within your existing Visual Basic 6.0 component development. Late-binding always requires two method calls for every call within the actual code: one to find information about the method (through automation and a process referred to as reflection), and one to invoke the method itself, necessitating two round-trips across the wire. Placing Option Strict at the top of your code module just helps to ensure that you don’t accidentally leave late-bound variables in your code.

Accessing COM/COM+ Objects Within the ASP.NET Environment–Don’t miss Shelley Powers’ first article on the differences between ASP.NET and the original ASP server environment. Shelley has also updated her book on ASP components within the Windows 2000/COM+ environment, Developing ASP Components, 2nd Edition.

All of these new techniques enforce a stricter adherence to a more strongly typed language, while still providing the option of more loosely typed conversions that do exist in many existing Visual Basic applications. This is a necessary compromise between the Visual Basic of today and the one included as part of .NET.

To ensure that your code moves cleanly into this more strongly typed environment, you can use the Option Explicitstatement now to enforce variable declarations in your current applications. Also, eliminate any narrowing conversions (converting numbers of larger precision and size to smaller data types, with the potential loss of data) in your code, and make use of explicit conversion functions when working with numbers and strings together:

StrSum = "Account is " & CStr(iValue) & " overdue"

In addition, use type libraries (included in your code module by attaching the libraries to your project) to perform early binding, not only for future compatibility, but also to improve the performance of your Visual Basic applications today.

When you open an existing VB 6.0 project in VB.NET, the upgrade wizard automatically adds the Option Strictstatement with a value of “Off” to provide for backwards compatibility in behavior. The Option Explicit statement is left as is (“off” by default).

Another .NET change to Visual Basic — and one that particularly impacts component developers — is the size of the integer data type, covered in the next section.

Integer Size

A significant data type change between the two releases of VB is the size of integer values. Starting with Visual Basic .NET, the Integer data type is equivalent to the new .NET System.Int32 data type, and is now 32-bits, and signed.

An advantage to 32-bit integers is that this size is more efficient within numeric operations than the older 16-bit integer, particularly on 32-bit operating systems, such as the current default Windows 2000 basic operating system.

Another benefit of the changed integer size is that VB is brought in line with other mainstream programming languages, such as C++, Java, and Perl. If you’ve worked with component development, particularly with components based in different languages, one of the most frustrating aspects of working with Visual Basic has been its 16-bit integer, especially when so many other languages have 32-bit integers. This is particularly apparent when accessing VB components from within PerlScript.

If you still want access to 16-bit numbers, you’ll need to use the new Short value, and use the Long data types for 64-bit values.

The upgrade wizard maintains the integrity of the VB application by converting VB integers to shorts (16-bit). If you want to ensure that your component is converted to the new .NET integer type, start using the VB 6.0 long data type for your variables and particularly your method parameters in your existing development effort.

A less significant data type change is that currency is no longer a supported data type. Instead, a new Decimal type has been provided to allow for more precision and more digits:

Dim decValue As Decimal

In Visual Basic 6.0, the Decimal data type was only available as a Variant sub-type.

Dates are also handled differently in Visual Basic .NET, and are implemented with the .NET DateTime format instead of the current Double format. To convert between the older and the new date format, Microsoft is providing routines such as ToDouble to convert the new data type to the original double value.

You can best prepare your existing code for these new data types by isolating your use of Date and Currency within your components as much as possible in order to manually migrate your code in the future if necessary.

Speaking of function parameters, another significant change within Visual Basic .NET is subroutine semantics, including a different parameter passing implementation.

Subroutine Modifications

Parameters, and how they are passed from the calling program are handled differently between VB 6.0 and VB.NET. By default in Visual Basic 6.0, all parameters are passed by reference if the ByVal keyword isn’t used. This allows the procedure to modify the variable used to pass the parameter in the calling program, which can lead to unexpected results, an example of which is:

Sub testValue(iNewValue As Integer)
   iNewValue = iNewValue + 20
End Sub

...

Dim iValue As Integer
iValue = 2

Call testValue(iValue)

' value is now 22 rather than 2

Parameters are passed by value as a default in Visual Basic .NET, protecting against accidental and unexpected data changes. You must explicitly use the ByRef keyword in order to pass a parameter by reference.

You can easily ensure the future compatibility of your existing code with Visual Basic .NET by using the explicit ByVal and ByRef keywords with all of your parameters in your 6.0 Visual Basic code.

The Optional parameter keyword also has different semantics in Visual Basic .NET. In 6.0 you can specify that a parameter is optional without having to provide a default value:

Sub someRoutine (Optional ByVal iValue As Integer)

In 6.0 you’d use IsMissing to check to see if the value changed. In Visual Basic .NET, you must supply a default value for all optional parameters:

Sub someRoutine (Optional ByVal iValue as Integer = 0)

To ensure smooth migration to .NET, when using Optional in your existing code, provide default values. This approach not only allows your code to move forward into .NET, it’s also a good programming practice to apply today – the use of IsMissing adds unnecessary complexity to your procedures.

Other changes with Visual Basic .NET have to do with structured data, such as arrays.

Structural Changes with Arrays

If you use arrays, you’ll find that you can no longer re-define the lower bound of an array with the Option Base statement in VB .NET:

Option Base 1

All arrays now start at zero, as arrays start in most programming languages. Again, this change is necessary for programming language interoperability, something that .NET tends to encourage (or at least, not discourage). In addition, you can’t specify a fixed array size in .NET as you could in 6.0:

Dim strValue(10) as String

Instead, you’ll use syntax similar to the following:

Dim iValue as Integer = new Integer(10) { }

This new approach allocates storage for 10 elements of the specified data type, but doesn’t fix the size of the array itself. The array can be changed through the use of the ReDim statement:

ReDim iValue(20)

To allow for maximum forward compatibility in your code, avoid the use of Option Base to reset the base value of an array. Not using this statement forces your arrays to begin with the zero boundary. The upgrade wizard will also convert arrays to being zero-based, if so instructed when the project is first opened.

Microsoft hasn’t restricted its Visual Basic changes to structural and data type changes. The use of built-in functions will also be impacted in .NET.

Built-in Functions and Namespaces

One brand new feature of Visual Basic .NET that I do want to mention in this article is the concept of namespaces. Namespaces are ways of exposing externally created components to an application, similar to importing a type library into C++ or attaching a reference to a type library in Visual Basic 6.0.

You can import a namespace into Visual Basic .NET code using the imports statement:

imports Microsoft.VisualBasic.ControlChars

With imports, you can reference members of the namespace without having to type the qualifying namespace name. Instead of:

dValue = Math.sqrt(number)

You can use:

dValue = sqrt(number)

The reason I’ve introduced the namespace concept into an article focusing on forward compatibility of VB ASP components is because many Visual Basic 6.0 built-in functions have now been defined within specific namespaces, such as the System.Math namespace, just shown.

One significant alteration to your code based on namespace use is with the String data type. Now, you can access Stringdirectly from within your code:

Dim strValue as String

In Visual Basic.NET, String is actually defined as part of the System.String namespace. In fact, all supported data types are now a part of the System namespace, as is much of VB’s built-in functionality.

To ensure backwards compatibility, Microsoft has provided a specific namespace, Microsoft.VisualBasic.Compatibility.VB6 that you can import into your existing Visual Basic 6.0 components. This will allow applications to work within the Visual Basic .NET environment until you have time to make the actual modifications.

One final change in Visual Basic .NET I’ll look at is the impact on Properties within the new environment, and the use of Set and Let.

Property Changes

In Visual Basic 6.0, you use direct assignment when assigning scalar values but must use the Set keyword when assigning an object to a variable:

Set obj = SomeObject

In Visual Basic.NET, the infrastructure supporting properties has changed, and the Set and Get keywords are now disallowed in the programming language.

As a demonstration of this change, in the past when you’ve worked with ADO, you’ve assigned a Connection object to a variable using syntax similar to the following:

Set rs.ActiveConnection = conn

Chances are, you’ve forgotten to use the Set keyword, resulting in an assignment of the Connection object’s default property, the connection string, instead of the object itself:

rs.ActiveConnection = conn

With the above, the code will still work, a database connection is assigned to the ResultSet object, but what happens is that a second connection is created using the connection string rather than using the existing connection object.

Visual Basic .NET no longer supports the concept of default properties unless they take parameters. This is one of the design changes folks have been asking for, and one that was long overdue.

With this type of change, the accidental assignment of a default property, as described with the ADO Connection object, will no longer occur – a definite improvement within the language and the tool.

The .NET infrastructure also specifies a new approach for defining properties that provides the means to set and retrieve the property value. An example of a property within the PDC-based release of Visual Basic .NET is the following:

' Internal storage, always in degrees. 
Dim Degrees As Double = 0  
  Property Angle(ByVal Radians As Boolean) As Double 
  Get 
    Angle = Degrees 
    If Radians Then Angle = Angle * 3.1415926536 / 180 
  End Get 
  Set 
    ' The keyword Value stands for the value passed in. 
    Degrees = Value    
    If Radians Then Degrees = Degrees * 180 / 3.1415926536 
  End Set 
  End Property

By providing a means to define how a property is set and retrieved, the Property Let, Property Set, and Property Getstatements are no longer necessary and been removed from language support. Again, as with many of the other changes detailed in this article, the upgrade wizard will automatically correct the use of Set and Get and property management when your VB 6.0 component project is opened. Compiled components that have been wrapped via the use of TlbImp aren’t impacted by these code internal changes.

Summary

You’ve not yet had a chance to get a detailed look at all of the Visual Basic .NET changes – many are still being determined. However, you should have a better understanding of the types of changes headed your way, and how they will impact your existing VB components and component development.

Hopefully I’ve also shown that though the changes are significant, they aren’t overwhelming. In fact, there are many steps you can take now that will allow for a smooth migration of your VB component code to the new .NET architecture.

As I finished writing this article, Microsoft announced that it was restoring some of the Visual Basic 6.0 functionality it had originally pulled with the first beta release of VB.NET. This move was to ensure that VB.NET could support applications developed before the release of VB.NET.

However, if you’re creating new applications–or components–adjust your code to be in synch with VB.NET rather than depending on support for the older VB code base.

Categories
Technology

O’Reilly P2P Presentation Proposal

Title: Smoke: An Infrastructure supporting Distributed Peer Services

Length: 60 minutes

Focus of Talk: Technical/Tutorial

Subject Matter: Infrastructure/Distributed Computation

Abstract

The sale of large scale control systems — such as those used with mass transit systems or to control multi-national pipelines — often requires a marketing and engineering effort that demands the input of several different people, many of whom live in different countries and speak different languages. To assist in this effort, a project is underway to create an automatic configuration tool that allows these team members to work in a collaborative manner, regardless of each member’s locale.

Because of a lack of infrastructure for applications of this nature, the developers designed one that is based entirely within P2P-based concepts and technologies.

This infrastructure, named Smoke, is unique in that it’s based on the concept of shared distributed peer services — services that are lightweight, discrete, and transient — existing within a framework that is both open-application and cross-platform compatible.

At the presentation, the speaker will provide an overview of Smoke, as well as demonstrate a working prototype of the automatic configuration tool. To display Smoke’s open-application and cross-platform support, three variations of the configuration tool prototype will be demonstrated: one with an interface created with Mozilla’s XUL and hosted on MacOS; one accessed through Enterprise Java Beans (EJB) hosted through an Apache WebServer and WebLogic on Unix; and one accessed through Groove, another P2P infrastructure product, hosted in Windows 2000.

Smoke is an open source infrastructure, which means it can be used by any developer interested in working within a P2P distributed peer services environment.

Description:

Shelley Powers will present an open source P2P infrastructure that supports the concept of distributed peer services: services that are lightweight, discrete, and transient. A prototype large scale control system configuration tool is used to demonstrate the infrastructure. Three different variations of the prototype will be shown, to demonstrate both the open-application and cross-platform capability of the infrastructure and the tool.

Speaker: Shelley Powers

Speaker Biography:

Shelley Powers is a consultant/author with her own company, the Burning Bird Corporation, currently located in Boston, Massachusetts.

In the last several years, Shelley has worked on several distributed and Web-based applications on a variety of platforms. In addition, she has also authored or co-authored books on Dynamic HTML, JavaScript, Java, CGI, Perl, P2P, and other technologies, as well as writing for several publications including Webtechniques, MSDN Journal, Netscapeworld, and O’Reilly Network. She’s the author of O’Reilly’s Developing ASP Components, second edition. Shelley can be reached at shelleyp@yasd.com.