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Visual Basic Concepts

Visual Studio 6.0

Optimizing Perceived Speed

Often the subjective speed of your application has little to do with how quickly it actually executes its code. To the user, an application that starts up rapidly, repaints quickly, and provides continuous feedback feels "snappier" than an application that just "hangs up" while it churns through its work. You can use a variety of techniques to give your application that "snap":

  • Keep forms hidden but loaded.

  • Preload data.

  • Use timers to work in the background.

  • Use progress indicators.

  • Speed the start of your application.

Keep Forms Hidden but Loaded

Hiding forms instead of unloading them is a trick that has been around since the early days of Visual Basic 1.0, but it is still effective. The obvious downside to this technique is the amount of memory the loaded forms consume, but it can't be beat if you can afford the memory cost and making forms appear quickly is of the highest importance.

Preload Data

You can also improve the apparent speed of your application by prefetching data. For example, if you need to go to disk to load the first of several files, why not load as many of them as you can? Unless the files are extremely small, the user is going to see a delay anyway. The incremental time spent loading the additional files will probably go unnoticed, and you won't have to delay the user again.

Use Timers to Work in the Background

In some applications you can do considerable work while you are waiting for the user. The best way to accomplish this is through a timer control. Use static (or module-level) variables to keep track of your progress, and do a very small piece of work each time the timer goes off. If you keep the amount of work done in each timer event very small, users won't see any effect on the responsiveness of the application and you can prefetch data or do other things that further speed up your application.

For More Information   To learn more about the timer control, see "Timer Control" in "Using Visual Basic’s Standard Controls." For a discussion of background processing, see "Interrupting Background Processing" in "Responding to Mouse and Keyboard Events."

Use Progress Indicators

When you can't avoid a long delay in your program, you need to give the user some indication that your application hasn't simply hung. Windows uses a standard progress bar to indicate this to users. You can use the ProgressBar control in the Microsoft Windows Common Controls included with the Professional and Enterprise editions of Visual Basic. Use DoEvents at strategic points, particularly each time you update the value of the ProgressBar, to allow your application to repaint while the user is doing other things.

At the very least, you should display the wait cursor to indicate the delay by setting the form’s MousePointer property to vbHourglass (11).

Speed the Start of Your Application

Apparent speed is most important when your application starts. Users' first impression of the speed of an application is measured by how quickly they see something after clicking on its name in the Start menu. With the various run-time DLLs that need to be loaded for Visual Basic for Applications, ActiveX controls, and so forth, some delay is unavoidable with any application. However, there are some things you can do to give a response to the user as quickly as possible:

  • Use Show in the Form_Load event.

  • Simplify your startup form.

  • Don’t load modules you don’t need.

  • Run a small Visual Basic application at startup to preload the run-time DLLs.

Use Show in the Form_Load Event

When a form is first loaded, all of the code in the Form_Load event occurs before the form is displayed. You can alter this behavior by using the Show method in the Form_Load code, giving the user something to look at while the rest of the code in the event executes. Follow the Show method with DoEvents to ensure that the form gets painted:

Sub Form_Load()
   Me.Show            ' Display startup form.
   DoEvents            ' Ensure startup form is painted.
   Load MainForm      ' Load main application fom.
   Unload Me         ' Unload startup form.
   MainForm.Show      ' Display main form.
End Sub

Simplify Your Startup Form

The more complicated a form is, the longer it takes to load. Keep your startup form simple. Most applications for Microsoft Windows display a simple copyright screen (also known as a splash screen) at startup; your application can do the same. The fewer controls on the startup form, and the less code it contains, the quicker it will load and appear. Even if it immediately loads another, more complicated form, the user will know that the application has started.

For large applications you may want to preload the most commonly used forms at startup so that they can be shown instantly when needed. A satisfying way to do this is to display a progress bar in your startup form and update it as you load each of the other forms. Call DoEvents after loading each form so that your startup form will repaint. Once all the important forms have been loaded, the startup form can show the first one and unload itself. Of course, each form you preload will run the code in its Form_Load event, so take care that this doesn't cause problems or excessive delays.

Don’t Load Modules You Don’t Need

Visual Basic loads code modules on demand, rather than all at once at startup. This means that if you never call a procedure in a module, that module will never be loaded. Conversely, if your startup form calls procedures in several modules, then all of those modules will be loaded as your application starts up, which slows things down. You should therefore avoid calling procedures in other modules from your startup form.

Run a Small Visual Basic Application at Startup to Preload the Run-time DLLs

A large part of the time required to start a Visual Basic application is spent loading the various run-time DLLs for Visual Basic, ActiveX, and ActiveX controls. Of course, if these are already loaded, none of that time need be spent. Thus users will see your application start up faster if there is another application already running that uses some or all of these DLLs.

One way to significantly improve the startup performance of your applications is to provide another small, useful application that the user always runs. For example, you might write a small application to display a calendar and install it in the startup group for Windows. It will then load automatically on system startup, and while it is useful in itself, it also ensures that the various Visual Basic run-time DLLs are loaded.

Finally, with the Professional and Enterprise editions of Visual Basic you can divide your application into a main skeleton application and several component executables or DLLs. A smaller main application will load faster, and it can then load the other parts as needed.

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