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Show/Hide Methods Versus Load/Unload Statements

The Load and Unload statements cause a form to load into memory or to unload from memory respectively. Both statements take the name of a form or a form variable as their parameter. For example, the statement

Load frmMain

would cause frmMain to load into memory, and the statement

Unload frmMain

would take it out of memory.

Although the Load statement brings a form into memory, it doesn't make the form visible. You must call the form's Show method or set its Visible property to True in order to make it visible to the user.

You might ask, since calling the Show method or setting the Visible property will load the form anyway, why bother ever using the Load statement?

You might also ask, since calling the Unload statement would make the form invisible anyway, why bother to ever use the Hide method?

VB provides programmers with both Load and Unload statements and Show and Hide methods because there are two different strategies for form management in an application. Which strategy you choose depends on how your application needs to balance speed of operation with efficient use of memory. The two strategies are:

  • Fast. Load all the forms you'll need in your application when your application begins to run. While the application is running, use only the Show and Hide methods of forms. Use only the Unload statement when your application is ending.

  • Memory Efficient. Load a form (either with the Show method or a combination of the Load statement and Show method) only when you need to use it. Immediately unload a form as soon as you don't need it in the application.

When you look at the Fast strategy, it might appear that there would be a big delay at the beginning of the program as your application loaded all the forms it was going to use. While this is objectively true, programmers usually cover up for the fact by supplying a "splash" screen to show the user flashy graphics as the application loads the forms. This is such a common technique in Windows programming that users have come to accept and even expect a delay of several seconds when a program begins to run. Once the forms are loaded, there will be no further delays as the application runs (because no forms will need to be loaded).

In reality, you'll find yourself using a combination of both the Fast and Memory Efficient strategies. Not every VB application, for example, will be able to load and maintain all of its forms in memory throughout the entire session of the application.

NOTE : Another Use of the Hide Method Even in the Memory Efficient model described here, there is a good reason to use Hide when the form needs to disappear instead of calling Unload immediately:

Consider the situation where you've loaded a form modally from elsewhere in your code. When the user dismisses the form, you might want to check the state of some of the form's controls by following these steps: From inside the modal form, you should close it with the Hide method. In your calling code, check the information you need from the form. Only then should you unload the form.


  

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