How to use variables in a Script Component

Case
I already explained how to use variables in a Script Task, but of cource you can use them in a Script Component as well.

Solution
There are two ways to read and write variables in a Script component. I will show you both. There is one big BUT for setting variables in a Script Component. You can't get the new variable value untill the Data Flow Task is finished. So you can't get its value within the same Data Flow Task.

1) Create variable
Let's create a integer variable called Counter.

Right mouse click in the Data Flow

2) Script component
Add a Script Component to your dataflow and give it a suitable name. In this example the type is  Transformation and the source is a csv file with some productnames and colors.

Script component

3) Input Columns
Select the columns you need in the script component. In this case we count blue colored products, so I need the color columns as readonly input column.

Input Columns

4a) Simple version
Add Counter to the ReadWriteVariables.

Let the script know what variables you want to use.

Now the script (only one row for setting the variable):

// C# code
public class ScriptMain : UserComponent
{
    // Counter variable for blue colors
    private int BlueCounter = 0;

    // When all rows are processed, set counter variable
    public override void PostExecute()
    {
        base.PostExecute();
        this.Variables.Counter = BlueCounter;
    }

    public override void Input0_ProcessInputRow(Input0Buffer Row)
    {
        // Count blue items
        if (Row.Color == "Blue")
        {
            // Add 1 to the BlueCounter variable
            BlueCounter++;
        }
    }
}

' VB.Net code
Public Class ScriptMain
    Inherits UserComponent

    ' Counter variable for blue colors 
    Private BlueCounter As Integer = 0

    ' When all rows are processed, set counter variable 
    Public Overrides Sub PostExecute()
        MyBase.PostExecute()
        Me.Variables.Counter = BlueCounter
    End Sub

    Public Overrides Sub Input0_ProcessInputRow(ByVal Row As Input0Buffer)
        ' Count blue items
        If (Row.Color = "Blue") Then
            ' Add 1 to the BlueCounter variable 
            BlueCounter = BlueCounter + 1
        End If
    End Sub
End Class

4b) Advanced Version
In the advanced version you don't add the variable to the ReadWrite list. We will do that in the code:

// C# code
public class ScriptMain : UserComponent
{
    // Counter variable for blue colors
    private int BlueCounter = 0;

    // When all rows are processed, set counter variable
    public override void PostExecute()
    {
        base.PostExecute();

        // Lock the variable for write
        VariableDispenser variableDispenser = (VariableDispenser)this.VariableDispenser;
        variableDispenser.LockForWrite("User::Counter");

        IDTSVariables100 vars;
        variableDispenser.GetVariables(out vars);

        // Set the variable
        vars["User::Counter"].Value = BlueCounter;

        // Unlock the variable
        vars.Unlock();
    }

    public override void Input0_ProcessInputRow(Input0Buffer Row)
    {
        // Count blue items
        if (Row.Color == "Blue")
        {
            // Add 1 to the BlueCounter variable
            BlueCounter++;
        }
    }
}

' VB.Net code
Public Class ScriptMain
    Inherits UserComponent
    Private BlueCounter As Integer = 0

    Public Overrides Sub PostExecute()
        MyBase.PostExecute()

        ' Lock the variable for write 
        Dim variableDispenser As VariableDispenser = CType(Me.VariableDispenser, VariableDispenser)
        variableDispenser.LockForWrite("User::Counter")

        ' Use IDTSVariables90 if you're using SSIS 2005 
        Dim vars As IDTSVariables100
        variableDispenser.GetVariables(vars)

        ' Set the variable 
        vars("User::Counter").Value = BlueCounter

        ' Unlock the variable 
        vars.Unlock()
    End Sub

    Public Overrides Sub Input0_ProcessInputRow(ByVal Row As Input0Buffer)
        ' Count blue items
        If (Row.Color = "Blue") Then
            ' Add 1 to the BlueCounter variable 
            BlueCounter = BlueCounter + 1
        End If
    End Sub
End Class

You can even add a Try Catch Finally construction to avoid unexpected errors (variable doesn't exists or is already locked). And if you move the vars.Unlock() row to the finally part, then you're certain that the variables are unlocked. Even if the Script Component fails. For an example see the last script of this Script Task article.

Which version is best? The result of both version is the same. The 'advanced' version gives you a little more control over what is happening and at what stage the variables are locked and released, but the simple version is used more often in forums and blogs. I recommend the simple method!

Update: I also wrote an SSIS WIKI about this where I also show how to use parameters in a Script Component