Detection of Backspace on KeyDown

Question

I am working on a silverlight web app. It interacts with a module that sends SMS's. I want to limit the text to 160 and show a counter. I did it like this:

public partial class SendSMSView
{
    public SendSMSView()
    {
       InitializeComponent();
       ApplyTheme();
    }

    protected void tbMessage_KeyDown(object sender, KeyEventArgs e)
    {
        count = 160 - this.tbMessage.Text.Length;
        this.lblCount.Content = count.ToString();
    }
}

This works fine for all the keys except backspace and delete. Of course it is made to function like this. i dug more on this and tried overriding keydown event so i added the following code snippet:

public class CustomTextBox : TextBox
{
    public CustomTextBox(): base()
    {
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        e.handler=false;
        base.OnKeyDown(e);
        //this place
    }
}

In OnKeyDown function i get all the key strokes registered. Setting Handler to false here doesnt help and still i cant get backspace to trigger tbMessage_KeyDow.

I want to somehow call the tbMessage_KeyDow function from //this place forcefully from there for backspace.

I searched MSDN, and found that IsInputKey can be overriden to return true so that onKeyDown responds to it as well, but My framework neither has IsInputKey nor PreviewKeyPress. Is there a workaround for getting backspace key registered as input key, or to call tbMessage_KeyDow [which is very crude approach] ? Please help.

Answer 1

try this ....

If you want to detect the backspace key on the key pressed in a textbox. we would suggest that you can try to do in the textbox's KeyUp event instead of the KeyDown event. for example:

   <TextBox x:Name="txt" KeyDown="txt_KeyDown" Text="Hello" KeyUp="txt_KeyUp"></TextBox>    

the codebehind:

    private void txt_KeyUp(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Back)
        {
            MessageBox.Show(this.txt.Text);
        }
    } 

or you can do like this...by creating a user control....

public partial class Page : UserControl {

    private TextBox TextBox1;

    public Page() {
        InitializeComponent();
        TextBox1 = new TextBox();
        Width = 300;
        Height = 100;
        LayoutRoot.Children.Add(textbox);
        OnTextChanged(((object)(sender)), ((TextChangedEventArgs)(e)));
        TextBox1.TextChanged;
        if (e.Key == Key.Back) {
            e.Handled = true;
        }
        else if (e.Key == Key.Delete) {
            e.Handled = true;
        }
    }
}