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Debug::WriteLineIf Method (Boolean, String)

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

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

[ConditionalAttribute(L"DEBUG")]
public:
static void WriteLineIf(
	bool condition, 
	String^ message
)

Parameters

condition
Type: System::Boolean

The conditional expression to evaluate. If the condition is true, the message is written to the trace listeners in the collection.

message
Type: System::String

A message to write.

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

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:

 if(mySwitch.TraceError) 
     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 TraceLevel Error or higher, the example outputs the first error message to the Listeners. For information about 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 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" );

public:
   static void MyErrorMethod()
   {
      // 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." );
      #endif
   }

.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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