iOS：使用UITextField子类在空的UITextField中检测退格

Question

The clear answer to detecting a backspace is by creating a subclass of UITextField and overriding the deleteBackward property.

I've created a subclass a UITextField subclass, but am getting this error:

'NSInvalidArgumentException', reason: '-[UITextField setMyDelegate:]: unrecognized selector sent to instance

This is my subclass code:

My TextField.h:

@protocol MyTextFieldDelegate <NSObject>
@optional
- (void)textFieldDidDelete;
@end

@interface MyTextField : UITextField<UIKeyInput>
//create "myDelegate"
@property (nonatomic, assign) id<MyTextFieldDelegate> myDelegate;
@end

My TextField.m:

- (void)deleteBackward {
    [super deleteBackward];

    if ([_myDelegate respondsToSelector:@selector(textFieldDidDelete)]){
        [_myDelegate textFieldDidDelete];
    }
}

In my ViewController that I would like to access the UITextField subclass I do the following:

 #import "MyTextField.h"

 <MyTextFieldDelegate>
 @property (nonatomic, strong) IBOutlet MyTextField *passcode1;
 self.passcode1.myDelegate = self;

Any ideas as to why I am getting the unrecognized selector error? It looks to me like I have done everything correctly in subclassing UITextField.

Answer 1

The problem is with your outlet. The property is defined with your custom class but in a Interface Builder you added a plain old UITextField. Hence the error at runtime. In Interface Buldier, update the text field's class to be your custom class.