TraceFilter.ShouldTrace Method (TraceEventCache, String, TraceEventType, Int32, String, Object(), Object, Object())


When overridden in a derived class, determines whether the trace listener should trace the event.

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

Public MustOverride Function ShouldTrace (
	cache As TraceEventCache,
	source As String,
	eventType As TraceEventType,
	id As Integer,
	formatOrMessage As String,
	args As Object(),
	data1 As Object,
	data As Object()
) As Boolean


Type: System.Diagnostics.TraceEventCache

The TraceEventCache that contains information for the trace event.

Type: System.String

The name of the source.

Type: System.Diagnostics.TraceEventType

One of the TraceEventType values specifying the type of event that has caused the trace.

Type: System.Int32

A trace identifier number.

Type: System.String

Either the format to use for writing an array of arguments specified by the args parameter, or a message to write.

Type: System.Object()

An array of argument objects.

Type: System.Object

A trace data object.

Type: System.Object()

An array of trace data objects.

Return Value

Type: System.Boolean

true to trace the specified event; otherwise, false.

Notes to Inheritors:

Implementations of this method should return true if the event specified by the passed parameters should be traced. Otherwise the method should return false. For example, a filter that allows only error events to pass through to the listener should inspect the eventType parameter and return true if the trace event type level is set to TraceEventType.Error or greater; otherwise, it should return false.

Implementations of the method should be prepared to handle null in the following parameters: args, data1, data, formatOrMessage, and cache. If the parameter value is null, the parameter is not part of the event. For example, if the args parameter is null, it means that the event does not have any arguments. If the data parameter is null, then there are either one or no data objects. If there is one data object, it will be found in the data1 parameter. The reason for the distinction between a single data object and an array of data objects is for performance. There is no reason to create an object array if only one object is traced, as is normally the case. If the data parameter is not null, the data1 parameter must also not be null.

It is guaranteed that the source parameter is not null and not an empty string ("").

Implementations of the method can optionally throw the following exceptions:

The following code example shows how to override the ShouldTrace method to indicate tracing should occur when the trace event type of the event is equal to TraceEventType.Error.

Public Class ErrorFilter
    Inherits TraceFilter

    Public Overrides Function ShouldTrace ( cache As TraceEventCache, _
                source As String, eventType As TraceEventType, _
                id As Integer, formatOrMessage As String, _
                args As Object(), data As Object, _
                dataArray As Object() ) As Boolean
        If eventType = TraceEventType.Error Then
            Return True
            Return False
        End If
    End Function
End Class

.NET Framework
Available since 2.0
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