Debug.WriteIf Method (Boolean, String)
Writes a message to the trace listeners in the Listeners collection if a condition is true.
Assembly: System (in System.dll)
'Declaration <ConditionalAttribute("DEBUG")> _ Public Shared Sub WriteIf ( _ condition As Boolean, _ message As String _ )
By default, the output is written to an instance of DefaultTraceListener.
This method calls the Write 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 WriteIf 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 Write. The second example always calls WriteIf, even when mySwitch.TraceError is false and no tracing output is produced. This can result in unnecessary execution of arbitrarily complex code.
if(mySwitch.TraceError) Debug.Write("aNumber = " + aNumber + " out of range");
Debug.WriteIf(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. Private Shared generalSwitch As New TraceSwitch("General", "Entire Application") Public Shared Sub MyErrorMethod() ' Write the message if the TraceSwitch level is set to Error or higher. Debug.WriteIf(generalSwitch.TraceError, "My error message. ") ' Write a second message if the TraceSwitch level is set to Verbose. Debug.WriteIf(generalSwitch.TraceVerbose, "My second error message.") End Sub 'MyErrorMethod