subclass override method not being called

问题:

I created a subclass of UITextField to override the method rightViewRectForBounds.

Here is my custom class CustomTextField

@interface CustomTextField : UITextField

@end

@implementation CustomTextField

// override rightViewRectForBounds method:
- (CGRect)rightViewRectForBounds:(CGRect)bounds{
    NSLog(@"rightViewRectForBounds");
    CGRect rightBounds = CGRectMake(bounds.origin.x + 10, 0, 30, 44);
    return rightBounds ;
}

@end

Now I set up my ViewController to call the custom class instead of UITextField.

#import "OutputViewController.h"
#import "CustomTextField.h"

@interface OutputViewController () <UITextFieldDelegate>

@property (strong, nonatomic) IBOutlet CustomTextField *field1;
@property (strong, nonatomic) IBOutlet UILabel *label1;

 - (void)methodName
{
self.field1.rightView = self.label1;
}

The property rightView should call my method override according to Apple's Documentation: "The right overlay view is placed in the rectangle returned by the rightViewRectForBounds: method of the receiver". Why isn't my override working?

Sorry if this is a bad question. I've only been programming for a month.

回答1:

The problem is most likely that field1 is not in fact a CustomTextField. It is easy to confirm this with a breakpoint or some logging.

Remember, it is not enough to declare the class of something. That thing must actually be that class (polymorphism). An instance has a class, quite without regard for how you may cast or declare a variable that refers to it.