Fail Method (String)
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Debug.Fail Method (String)


Emits the specified error message.

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

public static void Fail(
	string message


Type: System.String

A message to emit.

The default behavior is that the DefaultTraceListener outputs the message to a message box when the application is running in user interface mode and to the TraceListener instances in the Listeners collection.


The display of the message box is dependent 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 customize this behavior by adding a TraceListener to, or removing one from, the Listeners collection.

The following example uses the Fail method to print a message during exception handling.

catch (Exception) {
    Debug.Fail("Unknown Option " + option + ", using the default.");

You can also use the Fail method in a switch statement.

switch (option) {
    case Option.First:
       result = 1.0;

    // Insert additional cases.

       Debug.Fail("Unknown Option " + option);
       result = 1.0;

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