Don't raise TextChanged while continuous typing

Question

I have a textbox that has a fairly hefty _TextChanged event handler. Under normal typing condition the performance is okay, but it can noticeably lag when the u

Answer 1

One easy way is to use async/await on an inner method or delegate:

private async void textBox1_TextChanged(object sender, EventArgs e) {
    // this inner method checks if user is still typing
    async Task UserKeepsTyping() {
        string txt = textBox1.Text;   // remember text
        await Task.Delay(500);        // wait some
        return txt != textBox1.Text;  // return that text chaged or not
    }
    if (await UserKeepsTyping()) return;
    // user is done typing, do your stuff    
}

No threading involved here. For C# version older than 7.0, you can declare a delegate:

Func> UserKeepsTyping = async delegate () {...}

Please note, that this method will not secure you from occasionally processing the same "end reslut" twice. E.g. when user types "ab", and then immediately deletes "b", you might end up processing "a" twice. But these occasions shoud be rare enough. To avoid them, the code could be like this:

// last processed text
string lastProcessed;
private async void textBox1_TextChanged(object sender, EventArgs e) {
    // clear last processed text if user deleted all text
    if (string.IsNullOrEmpty(textBox1.Text)) lastProcessed = null;
    // this inner method checks if user is still typing
    async Task UserKeepsTyping() {
        string txt = textBox1.Text;   // remember text
        await Task.Delay(500);        // wait some
        return txt != textBox1.Text;  // return that text chaged or not
    }
    if (await UserKeepsTyping() || textBox1.Text == lastProcessed) return;
    // save the text you process, and do your stuff
    lastProcessed = textBox1.Text;   
}