如何检测 iOS 8 中 UITextField 上的删除键？

Question

I have subclassed UITextField and implemented the UIKeyInput protocol's deleteBackward method to detect backspace being pressed. This works fine on iOS 7 but not on iOS 8.

deleteBackward is not called on the UITextField anymore when I press the backspace key.

I've checked the documentation and the release notes and nothing points to the reason why this could happen. Any pointers?

Answer 1

A lot of people have been saying this is a bug, but being that this problem still exists in the GM I'm starting to think it might be a change in logic. With that said, I wrote this bit of code for my app and have tested it on iOS 7-8.

Add the following method to your UITextField subclass.

- (BOOL)keyboardInputShouldDelete:(UITextField *)textField {
    BOOL shouldDelete = YES;

    if ([UITextField instancesRespondToSelector:_cmd]) {
        BOOL (*keyboardInputShouldDelete)(id, SEL, UITextField *) = (BOOL (*)(id, SEL, UITextField *))[UITextField instanceMethodForSelector:_cmd];

        if (keyboardInputShouldDelete) {
            shouldDelete = keyboardInputShouldDelete(self, _cmd, textField);
        }
    }

    BOOL isIos8 = ([[[UIDevice currentDevice] systemVersion] intValue] == 8);
    BOOL isLessThanIos8_3 = ([[[UIDevice currentDevice] systemVersion] floatValue] < 8.3f);

    if (![textField.text length] && isIos8 && isLessThanIos8_3) {
        [self deleteBackward];
    }

    return shouldDelete;
}

This code is slightly before the red line of private API's, however you should have no problem using it. My app with this code is in the app store.

To explain a little, were calling the super implementation of this method to avoid losing code. After were going to call -deleteBackward if there is no text and the iOS version is between 8-8.2.

EDIT : 1/22/15

It also might be helpful to subclass the -deleteBackward method of your subclassed UITextField . This fixes a few conditional bugs. One being if you use a custom keyboard. Heres an example of the method.

- (void)deleteBackward {
    BOOL shouldDismiss = [self.text length] == 0;

    [super deleteBackward];

    if (shouldDismiss) {
        if ([self.delegate respondsToSelector:@selector(textField:shouldChangeCharactersInRange:replacementString:)]) {
            [self.delegate textField:self shouldChangeCharactersInRange:NSMakeRange(0, 0) replacementString:@""];
        }
    }
}

EDIT : 4/13/15

As @Gee.E commented, iOS 8.3 has fixed this issue. The code has been updated to reflect the changes.

Answer 2

You can detect when user deletes text by using backspace by implementing UITextField delegate method:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (range.length==1 && string.length==0)
        NSLog(@"backspace tapped");

    return YES;
}

Answer 3

You must look an example for MBContactPicker on github. Deletion of contacts at MBContactPicker via Backspace button on iOS8 tested by me. And it works greatly! You can use its as example.

Author of MBContactPicker use next method: When UITextField must become empty (or before call becomeFirstResponder when it is empty), he save single whitespace symbol there. And then when you press Backspace button (when focus was set to end of text of your UITextField), method

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

will work. Inside it you must use check like this:

NSString *resultString = [textField.text stringByReplacingCharactersInRange:range withString:string];
BOOL isPressedBackspaceAfterSingleSpaceSymbol = [string isEqualToString:@""] && [resultString isEqualToString:@""] && range.location == 0 && range.length == 1;
if (isPressedBackspaceAfterSingleSpaceSymbol) {
    //  your actions for deleteBackward actions
}

So, you must always control that UITextField contains single whitespace.

This is not hack. So, user willn't noticed about some behaviour was changed

Answer 4

Swift 2.2:

func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool {

    if text == "" {
      print("Backspace has been pressed")
    }

    return true
}

Answer 5

In iOS8, some custom keyboards delete whole word, so only check string.length is OK.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (string.length==0) { //Delete any cases
       if(range.length > 1){
          //Delete whole word
       }
       else if(range.length == 1){
          //Delete single letter
       }
       else if(range.length == 0){
          //Tap delete key when textField empty
       }  
    }  
    return YES;
}

Answer 6

This does not explicitly answer the original question but worth nothing that in the documentation for textField(_:shouldChangeCharactersIn:replacementString:) , it says:

" string : The replacement string for the specified range. During typing, this parameter normally contains only the single new character that was typed, but it may contain more characters if the user is pasting text. When the user deletes one or more characters, the replacement string is empty."

Thus, we can detect backspaces in a UITextFieldDelegate if we implement textField(_:shouldChangeCharactersIn:replacementString:) and check if the length of string is 0.

A lot of other answers here have used this same logic without referencing the documentation so hopefully getting it right from the source makes people more comfortable using it.

Answer 7

Swift 2.0 version for Detecting BackSpace based deletion, referencing code post from almas

//For Detecting Backspace based Deletion of Entire Word in TextField
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { 
    if (range.length == 1 && string.isEmpty){
        print("Used Backspace")
    }
return true
}

Answer 8

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
   const char * _char = [string cStringUsingEncoding:NSUTF8StringEncoding];
   int isBackSpace = strcmp(_char, "\b");

   if (isBackSpace == -8) {
     NSLog(@"Backspace was pressed");
   }

return YES;

}

Basically this method detects which button you are pressing (or have just pressed). This input comes in as an NSString. We convert this NSString to a C char type and then compare it to the traditional backspace character (\\b). Then if this strcmp is equal to -8, we can detect it as a backspace.

Answer 9

swift 2:

if (string.characters.count == 0 && range.length == 1) {
            return true
}

you should use like this string.characters.count

Answer 10

func keyboardInputShouldDelete(_ textField: UITextField) -> Bool { }

This function is called when you hit delete key