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Assert Method (Boolean, String)

Debug.Assert Method (Boolean, String)

Checks for a condition; if the condition is false, outputs a specified message and displays a message box that shows the call stack.

Namespace:  System.Diagnostics
Assemblies:   System.Diagnostics.Debug (in System.Diagnostics.Debug.dll)
  System (in System.dll)

'Declaration
<ConditionalAttribute("DEBUG")> _
Public Shared Sub Assert ( _
	condition As Boolean, _
	message As String _
)

Parameters

condition
Type: System.Boolean

The conditional expression to evaluate. If the condition is true, the specified message is not sent and the message box is not displayed.

message
Type: System.String

The message to send to the Listeners collection.

By default, the Debug.Assert method works only in debug builds. Use the Trace.Assert method if you want to do assertions in release builds. For more information, see Assertions in Managed Code.

Typically, the Assert method is used to identify logic errors during program development. Assert evaluates the condition. If the result is false, it sends the specified diagnostic message to the Listeners collection. You can customize this behavior by adding a TraceListener to, or removing one from, the Listeners collection.

When the application runs in user interface mode, it displays a message box that shows the call stack with file and line numbers. The message box contains three buttons: Abort, Retry, and Ignore. Clicking the Abort button terminates the application. Clicking Retry sends you to the code in the debugger if your application is running in a debugger, or offers to open a debugger if it is not. Clicking Ignore continues with the next instruction in the code.

NoteNote

The display of the message box depends on the presence of the DefaultTraceListener. If the DefaultTraceListener is not in the Listeners collection, the message box is not displayed. The DefaultTraceListener can be removed by the <clear> Element for <listeners> for <trace>, the <remove> Element for <listeners> for <trace>, or by calling the Clear method on the Listeners property (System.Diagnostics.Trace.Listeners.Clear()).

You can change the behavior of the DefaultTraceListener in the configuration file that corresponds to the name of your application. In this file, you can enable and disable the assert message box or set the DefaultTraceListener.LogFileName property. The configuration file should be formatted as follows:

<configuration>
  <system.diagnostics>
    <assert assertuienabled="true" logfilename="c:\\myFile.log" />
  </system.diagnostics>
</configuration>

The following example checks whether the type parameter is valid. If type is Nothing, Assert outputs a message.

Public Shared Sub MyMethod(type As Type, baseType As Type)
    Debug.Assert(Not (type Is Nothing), "Type parameter is null")
End Sub 'MyMethod 

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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