Pragma Directives

From Xojo Documentation


Used to suspend and/or override actions to improve code execution times, issue warnings or error messages, and change/modify other normal operations. When a pragma directive is used to disable an automatic task, the task remains off until the end of the method in which it is called (or is enabled by calling it again and specifying True), but not in other methods that might be called within the original method. Some pragma commands can be turned on and off within a method. Refer to the list below for specifics.


#Pragma Directive
#Pragma Directive True or False

Directive Description
BackgroundTasks Enables or disables auto-yield to background threads.

In addition to the pragma directive, specify True or False. Setting this directive to False is the same as using DisableBackgroundTasks. You may place this pragma anywhere within the method to enable or disable background threads as necessary.

#Pragma BackgroundTasks False
BoundsChecking Enables or disables bounds checking.

In addition to the pragma directive, specify True or False. Specifying False is the same as using DisableBoundsChecking. You may place this pragma anywhere within the method to enable or disable bounds checking as necessary.

#Pragma BoundsChecking False
BreakOnExceptions Used to override the BreakOnExceptions menu item in the IDE. The possible values are: True, False, and Default. You may place this pragma anywhere within the method to enable or disable breaking on exceptions as necessary.
#Pragma BreakOnExceptions False
DisableAutoWaitCursor Used to disable the automatic display of the wait cursor (or watch cursor).

The scope of this pragma is local. The wait cursor will be disabled in the method that calls the pragma until the method ends. For example, if DisableAutoWaitCursor is called in a Pushbutton that runs a loop, the wait cursor will be disabled only until the loop runs and the Action event has completed.

DisableBackgroundTasks Used to disable calls to the framework inside of loop iterations to see if it needs to switch threads or perform other tasks (such as polling the debugger socket in a debug build). It is specific to the scope the pragma is in and does not affect other methods you may call from your method. It also does not disable preemptive thread switching in the OS itself.

Using this pragma can speed up very processor-intensive operations.

#Pragma DisableBackgroundTasks
Do not use DisableBackgroundTasks within web applications as it will prevent other sessions from running until the background tasks are resumed. This could cause sessions to disconnect or other undesired behavior.
DisableBoundsChecking Used to turn off array bounds checking on array index values in code after the #pragma.
#Pragma DisableBoundsChecking
Error Used to generate a compile error manually, preventing your project from compiling. Useful for reminding you of code you have to update.
#Pragma Error "Fix the code!"
NilObjectChecking Controls whether to automatically check objects for Nil before accessing properties and calling methods.

In addition to the pragma directive, specify True or False.

#Pragma NilObjectChecking False
Introduced 5.0
Controls whether to check for stack overflows.

In addition to the pragma directive, specify True or False. You may place this pragma anywhere within the method to enable or disable stack overflow checking as necessary.

#Pragma StackOverflowChecking False
Unused VariableName Controls whether Analyze Project will test for the passed unused variable. VariableName can be a local variable, method parameter, or event parameter. You must pass the variable or parameter you do not want to test. The pragma can be used only after the variable has been declared. Also, you cannot pass a list of variables. Use a separate #pragma statement for each variable. You can also turn off checking within the Issues pane by clicking the Type Filter button In the Issues toolbar and deselecting the checks for unknown local variable, method parameter, or event parameter.
#Pragma Unused Column
Warning Used to issue a warning manually. Useful to remind you of code to fix. This warning only appears when you check your project for errors.
#Pragma Warning "Fix this code!"
X86CallingConvention Accepts either StdCall or CDecl, not True or False. Allows you to determine which calling convention a method will be compiled with on x86.

This allows you to write callback functions on Windows, which typically require the StdCall calling convention.

#Pragma X86CallingConvention StdCall


The pragma directives BackgroundTasks, BoundsChecking, BreakOnExceptions, NilObjectChecking and StackOverflowChecking can be enabled or disabled within the method. The setting is tied to the enclosing scope. So, for example, if it's in an 'if' block, it will be reset to the outer value when the scope is exited.

Sample Code

This example disables background tasks for the inner loop, but leave them enabled for the outer loop:

For y = 0 To Height
#Pragma BackgroundTasks False
For x = 0 To Width
//...process some pixels...

#Pragma BackgroundTasks True

The following example shows how the BreakOnExceptions pragma can be used to turn off the feature for a particular code snippet. This is handy when you have a specific exception that you do not want to cause the debugger to appear:

#Pragma BreakOnExceptions False
Var f As FolderItem
f.Visible = True
Catch err As NilObjectException
End Try

// Reset to its default state
#Pragma BreakOnExceptions Default