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You are here: Visual Basic > Advanced VB6 tutorial > Chapter 18

Watch Contexts

After you have entered an expression to watch, you need to tell VB about the context in which the watch should be active. Remember that the watch expression must be in the scope of the currently executing code for VB to tell you its value. If you specify a context in which the expression isn’t valid, you will see the Expression not defined in context message. Again, that message doesn’t necessarily mean that you have entered a bad expression. It does pay, however, to check the entry just in case.

If you don’t have a form or module open when you create your watch, the context options for your watch defaults to all procedures and all modules.

If you accept the default context options, the expression is evaluated constantly throughout the entire project. Such a broad setting may sometimes make sense (as for a global variable, for instance), but you will make VB work harder if you monitor Watch expressions in every possible context. The narrower the scope, the faster you see the results. Bear in mind that the goal of a watch is to locate a problem in your code, such as a failure to modify a variable or assigning it a bad value.

If you have some idea of where the problem is, it makes sense to limit the watch to a more appropriate context. When you set a watch, VB will change the module context setting for you to default to the form or module you are currently viewing, as shown in Figure 18.4.

You can limit the scope of your Watch expression to a single module.
FIGURE 18.4 You can limit the scope of your Watch expression to a single module.

The default procedure selection is also context sensitive. If the cursor is in a particular procedure, it will be used as the default scope, as shown in Figure 18.5.

You can also limit the scope of a Watch expression to a particular procedure.
FIGURE 18.5 You can also limit the scope of a Watch expression to a particular procedure.

If you have an expression selected in a code window, the value of the Watch expression defaults to it too. If you want to watch a variable, you don’t need to highlight its entire name—the word in which the cursor appears will be used by default. Of course, you aren’t locked into the defaults. You can type a different expression for the watch if the default isn’t what you want. If you need to select a different scope, you can select from a list of the modules and procedures in the current project, as shown in Figure 18.6.

Use the combo boxes to change the module or procedure scope of a Watch expression.
FIGURE 18.6 Use the combo boxes to change the module or procedure scope of a Watch expression.


  

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