Coding a Custom Foreach Enumerator

项目
12/15/2008

After you have created a class that inherits from the ForEachEnumerator base class, and applied the DtsForEachEnumeratorAttribute attribute to the class, you must override the implementation of the properties and methods of the base class to provide your custom functionality.

For a working sample of a custom enumerator, see ForEachDirectory 示例.

Implementing the Enumerator

Initializing the Enumerator

You can override the InitializeForEachEnumerator method to cache references to the connection managers defined in the package, and to the events interface that you can use to raise errors, warnings, and informational messages.

Validating the Enumerator

The Validate method is overridden to verify that the enumerator is correctly configured. If you return Failure from the method, the enumerator and the package that contains the enumerator will not be executed. The implementation of this method is specific to each enumerator, but if the enumerator relies on Variable or ConnectionManager objects, you should add code to verify that these objects exist in the collections that are provided to the method.

The following code example demonstrates an implementation of Validate that checks for a variable specified in a property of the enumerator.

private string variableNameValue;

public string VariableName
{
    get{ return this.variableNameValue; }
    set{ this.variableNameValue = value; }
}

public override DTSExecResult Validate(Connections connections, VariableDispenser variableDispenser, IDTSInfoEvents infoEvents, IDTSLogging log)
{
    if (!variableDispenser.Contains(this.variableNameValue))
    {
        infoEvents.FireError(0, "MyEnumerator", "The Variable " + this.variableNameValue + " does not exist in the collection.", "", 0);
            return DTSExecResult.Failure;
    }
    return DTSExecResult.Success;
}

Private variableNameValue As String
 
Public Property VariableName() As String
    Get 
         Return Me.variableNameValue
    End Get
    Set (ByVal Value As String) 
         Me.variableNameValue = value
    End Set
End Property
 
Public Overrides Function Validate(ByVal connections As Connections, ByVal variableDispenser As VariableDispenser, ByVal infoEvents As IDTSInfoEvents, ByVal log As IDTSLogging) As DTSExecResult
    If Not variableDispenser.Contains(Me.variableNameValue) Then
        infoEvents.FireError(0, "MyEnumerator", "The Variable " + Me.variableNameValue + " does not exist in the collection.", "", 0)
            Return DTSExecResult.Failure
    End If
    Return DTSExecResult.Success
End Function

Returning the Collection

During execution, the ForEachLoop container calls the GetEnumerator method of the custom enumerator. In this method, the enumerator creates and populates its collection of items, and then returns the collection. The ForEachLoop then iterates the items in the collection, and executes its control flow for each item in the collection.

The following example shows an implementation of GetEnumerator that returns an array of random integers.

public override object GetEnumerator()
{
    ArrayList numbers = new ArrayList();

    Random rand = new Random(DateTime.Now);

    for( int x=0; x < 100; x++ )
        numbers.Add( rand.Next());

    return numbers;
}

Public Overrides Function GetEnumerator() As Object
    Dim numbers As ArrayList =  New ArrayList() 
 
    Dim rand As Random =  New Random(DateTime.Now) 
 
        Dim x As Integer
        For  x = 0 To  100- 1  Step  x + 1
        numbers.Add(rand.Next())
        Next
 
    Return numbers
End Function

请参阅

任务

Creating a Custom Foreach Enumerator
Developing a User Interface for a Custom ForEach Enumerator

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