Debug.Fail Method (String, String)


Emits an error message and a detailed error message.

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

Public Shared Sub Fail (
	message As String,
	detailMessage As String


Type: System.String

A message to emit.

Type: System.String

A detailed 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 e As Exception
    Debug.Fail("Invalid value: " + value.ToString(), "Resetting value to newValue.")
    value = newValue
End Try

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

Select Case option1
    Case MyOption.First
        result = 1.0

    ' Insert additional cases.
    Case Else
        Debug.Fail("Unknown Option " & option1, "Result set to 1.0")
        result = 1.0
End Select

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