Determine when and which character is added or del

Question

I have a simple text box in a WPF application.

I need to know when a character was added/deleted in the text box, which character and where it was added or deleted.

I thought about using the TextBox.KeyDown event, but it has some problems:

• I can't know where the character was added or deleted.
• I have no idea how to determine which character was added (from the KeyEventArgs).

Any ideas?

Answer 1

You can use a "brute force" method - the text box (in winforms and I think in WPF as well) has a text changed event you can use and by comparing the text before the event and the current text you can find what character has been added or removed.

Answer 2

Found the solution. In WPF, the TextBox.TextChanged event has a TextChangedEventArgs. In this class, there is a property named Changes.

Here's my code:

private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
{
    foreach (var change in e.Changes)
    {
        if (change.AddedLength > 0 && change.RemovedLength == 0)
        {
            if (change.AddedLength == 1)
            {
                AddCharacter(textBox1.Text[change.Offset], change.Offset);
            }
            else
            {
                AddString(textBox1.Text.Substring(change.Offset, change.AddedLength), change.Offset);  
            }
        }
        else if (change.AddedLength == 0 && change.RemovedLength > 0)
        {
            if (change.RemovedLength == 1)
            {
                RemoveCharacter(change.Offset);
            }
            else
            {
                RemoveString(change.Offset, change.RemovedLength + change.Offset);
            }
        }
        else if (change.AddedLength == 1 & change.RemovedLength == 1)
        {
            ReplaceCharacter(change.Offset, textBox1.Text[change.Offset]);
        }
        else
        {
            ReplaceString(change.Offset, change.Offset + change.RemovedLength, textBox1.Text.Substring(change.Offset, change.AddedLength));
        }
    }
}

Now I just need to wait two days to accept this answer. :)

Thanks anyway.