Trace.Assert Method (Boolean, String, String)
Checks for a condition; if the condition is false, outputs two specified messages and displays a message box that shows the call stack.
Assembly: System (in System.dll)
'Declaration <ConditionalAttribute("TRACE")> _ Public Shared Sub Assert ( _ condition As Boolean, _ message As String, _ detailMessage As String _ )
- Type: System.Boolean
The conditional expression to evaluate. If the condition is true, the specified messages are not sent and the message box is not displayed.
Typically, the 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 and detailed 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.
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> <switches> <add name="mySwitch" value="4"/> </switches> <trace autoflush="false" indentsize="4"/> <assert assertuienabled="true" logfilename=".\TraceLog.txt"/> </system.diagnostics> </configuration>
The following example checks to see that the type parameter is valid. If the type passed in is Nothing, the Assert outputs a message.