Question

I have a TextChanged event for my WPF TextBox as follows:

private void textMatch_TextChanged(object sender, TextChangedEventArgs e)
{
    var m = e.Changes;//here I can see e.Changes has what I'm looking for
    //do some other stuff here.
}

However, what I want to do is to check the length of text that was added. Apparently, e.Changes contains that value but I can’t figure out a way to find it out programmatically neither could I find any example online.

My current way of checking this is by storing the current length each time text is changed and making sure the new length only increases by 1 but It’s sorta like hacking to me.

Has anyone tried this before? How do I find out the length of the added text using the TextChangedEventArgs? Thanks.

Answer 1

What you’re looking for is how to extract the TextChange object from the e.Changes TextChange collection. The following should work:

int added = e.Changes.ElementAt(0).AddedLength;

However, if you want something that looks more specific you could use:

int added = e.Changes.FirstOrDefault().AddedLength;

Since e.Changes as far as I know at the moment will always contain a single TextChange item, I guess it will always be the first even in future implementations of the WPF TextBox.

For Non-Linq implementation which seems really unnecessary to me you can use the following bulky code:

var x = e.Changes.GetEnumerator();
x.MoveNext();
int added = x.Current.AddedLength;