Paste Event in a WPF TextBox

Question

I have created a custom control inheriting TextBox. This custom control is a numeric TextBox, only supporting numbers.

I am using OnP

Answer 1

This works pretty good for me. I wanted to changed the color of the textbox when the user made a change to the contents.

• accept numbers, including period and negative characters
• keys typed: delete, backspace, ctrl-V (paste), ctrl-X (cut)
• right mouse click for paste and cut

I was able to achieve it with the 3 events below:

    public bool IsDirty {
        set {
            if(value) {
                txtValue.Background = Brushes.LightBlue;
            } else {
                txtValue.Background = IsReadOnly ? Brushes.White : Brushes.LightYellow;
            }
        }
        get {
            return txtValue.Background == Brushes.LightBlue;
        }
    }

    private void PreviewTextInput(object sender, TextCompositionEventArgs e) {
        TextBox tb = ((TextBox)sender);
        string originalText = tb.Text;
        string newVal = "";

        //handle negative
        if (e.Text=="-") {
            if(originalText.IndexOf("-") > -1 || tb.CaretIndex != 0 || originalText == "" || originalText == "0") {
                //already has a negative or the caret is not at the front where the - should go
                //then ignore the entry
                e.Handled = true;
                return;
            }

            //put it at the front
            newVal = e.Text + originalText;
        } else {
            //normal typed number
            newVal = originalText + e.Text;
        }

        //check if it's a valid double if so then dirty
        double dVal;
        e.Handled = !double.TryParse(newVal, out dVal);
        if(!e.Handled) {
            IsDirty = true;
        }
    }

    private void PreviewKeyUp(object sender, KeyEventArgs e) {
        //handle paste
        if ((Key.V == e.Key || Key.X == e.Key) && Keyboard.Modifiers ==  ModifierKeys.Control) {
            IsDirty = true;
        }
        //handle delete and backspace
        if (e.Key == Key.Delete || e.Key == Key.Back) {
            IsDirty = true;
        }
    }


    private void PreviewExecuted(object sender, ExecutedRoutedEventArgs e) {
        //handle context menu cut/paste
        if (e.Command == ApplicationCommands.Cut || e.Command == ApplicationCommands.Paste) {
            IsDirty = true;
        }
    }