Question

I have a textbox, when textchange event fired, I want to compare the old value with the changed value.

How to get the old value?

Answer 1

Register the KeyDown-Event of the TextBox. This is event is raised when a Key is pressed and before the TextChanged-Event of the TextBox is raised.

In this event, you can get the current Text by calling the Text-Property of the TextBox.

TextBox myTextBox = new TextBox();
myTextBox.KeyDown += KeyDownOnMyTextBox;
myTextBox.TextChanged += TextChangedOnMyTextBox;

string currentText = string.Empty;
string newText = string.Empty;

private void KeyDownOnMyTextBox(object sender, KeyEventArgs e){
  currentText = myTextBox.Text;
}

private void TextChangedOnMyTextBox(object sender, TextChangedEventArgs e){
  newText = myTextBox.Text;
}