Pass Data from Child Window to MainWindow TextBlock

Question

In this example, MainWindow has a button that opens Window2.

Window2 has a button that writes \"Hello, World!\" to MainWindo

Answer 1

The 'proper' way usually depends on what your needs and circumstances are. But in general, using a delegate to pass data between windows is a common and standard practice.

Lets say the data you want to pass is a string. In your Main window, you want to create a delegate that lets you pass a string. Then you create an instance of that delegate type and subscribe a method that matches. Then when you open your secondary window, you pass that delegate to your secondary window.

public delegate void DataTransfer(string data);

public partial class MainWindow : Window
{
    public DataTransfer transferDelegate;

    public MainWindow()
    {
        InitializeComponent();
        transferDelegate += new DataTransfer(DataMethod);
    }

    public void DataMethod(string data)
    {
        // Do what you want with your data.
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Window2 win = new Window2(transferDelegate);
        win.Show();
    }
}

Now, when you invoke that delegate in your secondary window, the DataMethod() of your Form1 gets called, and so you can pass information between windows.

Your secondary window implementation should look like this:

public partial class Window2 : Window
{
    DataTransfer transferDel;

    public Window2(DataTransfer del)
    {
        InitializeComponent();
        transferDel = del;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        string data = "Hello, World!"; // Your string data to pass.
        transferDel.Invoke(data);
    }
}

As you can see, when you invoke the delegate that was passed, it calls the corresponding method in your main program.

One stand out advantage of this method is that you don't need to pass an instance of MainWindow to your Window2, you simply use delegates and subscribed methods to pass data between the two instances of windows.