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Trace.Assert Method (Boolean, String, String)

Checks for a condition, and displays both messages if the condition is false.

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

<ConditionalAttribute("TRACE")> _
Public Shared Sub Assert ( _
	condition As Boolean, _
	message As String, _
	detailMessage As String _
Dim condition As Boolean
Dim message As String
Dim detailMessage As String

Trace.Assert(condition, message, detailMessage)
/** @attribute ConditionalAttribute("TRACE") */ 
public static void Assert (
	boolean condition, 
	String message, 
	String detailMessage
public static function Assert (
	condition : boolean, 
	message : String, 
	detailMessage : String
Not applicable.



true to prevent a message being displayed; otherwise, false.


A message to display.


A detailed message to display.

Typically, you use Assert to identify logic errors during program development. Assert will evaluate the condition. If the result is false, it sends diagnostic messages to the Listeners.

The default behavior is to display a message box when the application runs in user-interface mode, and to output the message to the default trace output. You can customize this behavior by adding a TraceListener to, or removing one from, 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()).

To set an assert, you can also edit the configuration file that corresponds to the name of your application. Within this file, you can enable and disable the assert or set the name of its log file. The configuration file should be formatted like the following example:

      <add name="mySwitch" value="4"/>
    <trace autoflush="false" indentsize="4"/>
    <assert assertuienabled="true" logfilename=".\TraceLog.txt"/>

The following example checks to see that the type parameter is valid. If the type passed in is a null reference (Nothing in Visual Basic), the Assert outputs a message.

Public Shared Sub MyMethod(type As Type, baseType As Type)
    Trace.Assert( Not (type Is Nothing), "Type parameter is null", _
        "Can't get object for null type")

    ' Perform some processing.
End Sub

public static void MyMethod(Type type, Type baseType)
    Trace.Assert(type != null, "Type parameter is null", 
        "Can't get object for null type");
    // Perform some processing.
} //MyMethod

function MyMethod(type : Type, baseType : Type)
   Trace.Assert(type != null, "Type parameter is null", "Can't get object for null type")
   // Perform some processing.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0