Notifications of backspace key iOS - ios

Question

Is there a way to get notifications of when the user presses the backspace key on a UITextField, even if the field is empty?
I would like to be able to trigger some code when the user backspaces on an empty field.

Answer 1

[[NSNotificationCenter defaultCenter] addObserver: self selector: #selector(keyPressed:) name: UITextFieldTextDidChangeNotification object: nil];
This is how you get notified on every key the user presses. Then you have to figure out (i think in the notification is a property for it) which key was pressed.
Or you can use the textfield delegate function
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
To figure out what key was pressed

Answer 2

I can think of a technique to get you what you want but its going to take a bit of code. In essence, always keep a single Unicode "space" character at the front of the string. I don't have my book with me, but there is a really thin space character you can use.
You will put most of your code here:
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
when the field begins editing, prefix any string there with the space
when the user appends text as seen in shouldChangeCharactersInRange, append it.
if the user tries to delete the final last character, or a range that contains it, then return NO, make the change, then add back the leading space char.
when the textField is finished editing, remove the leading space

Answer 3

Since you need to detect not when text was deleted but when the backspace key is pressed, you need to do quite a bit more than implement UITextFieldDelegate.
Read this blog post about how UITextField forwards all the UIKeyInput methods to a private class UIFieldEditor. The writer dynamically subclasses UIFieldEditor at runtime in order to detect these events.
Hope this points you in the right direction!

Answer 4

This will detect backspace. Now you can do whatever when backspace is pressed.
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
if (textField==txtMobileNo)
{
const char * _char = [string cStringUsingEncoding:NSUTF8StringEncoding];
int isBackSpace = strcmp(_char, "\b");
if (isBackSpace == -8) {
NSLog(#"isBackSpace");
if (textField.text.length == 9)
{
}
return YES; // is backspace
}
else if (textField.text.length == 10) {
return YES;
}
}
return NO;
}