Debug::WriteLineIf Method (Boolean, String^, String^)


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Writes a category name and message to the trace listeners in the Listeners collection if a condition is true.

Namespace:   System.Diagnostics
Assembly:  System (in System.dll)

static void WriteLineIf(
	bool condition,
	String^ message,
	String^ category


Type: System::Boolean

true to cause a message to be written; otherwise, false.

Type: System::String^

A message to write.

Type: System::String^

A category name used to organize the output.

By default, the output is written to an instance of DefaultTraceListener.

The category parameter can be used to group output messages.

This method calls the TraceListener::WriteLine method of the trace listener.

Notes to Implementers:

You can minimize the performance penalty of instrumenting your application by using If...Then statements instead of using WriteLineIf statements. The following two code examples send the same debugging message. However, the first example is much faster when tracing is off, because if mySwitch.TraceError evaluates to false, you do not call WriteLine. The second example always calls WriteLineIf, even when mySwitch.TraceError is false and no tracing output is produced. This can result in unnecessary execution of arbitrarily complex code.

First example:

    Debug.WriteLine("aNumber = " + aNumber + " out of range");

Second example:

Debug.WriteLineIf(mySwitch.TraceError, "aNumber = " + aNumber + " out of range");

The following example creates a TraceSwitch named generalSwitch. This switch is set outside of the code sample.

If the switch is set to the TraceLevelError or higher, the example outputs the first error message to the Listeners. For information on adding a listener to the Listeners collection, see the TraceListenerCollection class.

Then, if the TraceLevel is set to Verbose, the example outputs the second error message and the category on the same line as the first message. A line terminator follows the second message.

   // Class-level declaration.
   // Create a TraceSwitch.
   static TraceSwitch^ generalSwitch = 
      gcnew TraceSwitch( "General","Entire Application" );

   static void MyErrorMethod( String^ category )
      // Write the message if the TraceSwitch level is set to Error or higher.
      #if defined(DEBUG)
      Debug::WriteIf( generalSwitch->TraceError, "My error message. " );

      // Write a second message if the TraceSwitch level is set to Verbose.
      Debug::WriteLineIf( generalSwitch->TraceVerbose, 
         "My second error message.", category );

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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