协议可选方法在未实现时发生崩溃

Question

I am using protocol with some optional methods used

#import <UIKit/UIKit.h>
@class TextViewTableViewCell;

@protocol TextViewTableViewCellDelegate

@optional
- (void)textViewDidChange:(UITextView *)textView forIndexPath:(NSIndexPath *)indexPath;
- (void)textViewTableViewCellDoneTyping:(UITextView *)textView forIndexPath:(NSIndexPath *)indexPath;
- (BOOL)shouldChangeEditTextCellText:(TextViewTableViewCell *)cell newText:(NSString *)newText;

@end

@interface TextViewTableViewCell : UITableViewCell <UITextViewDelegate>

But it is giving crash if I'am using any of the function in the class i implemented this protocol

I don't know why this is happening. According to me optional method is not compulsory to use.

it giving crash on this method when the delegate function is called and we call the protocol method

- (void)textViewDidChange:(UITextView *)textView
{
[self.delegate textViewDidChange:self.textView forIndexPath:self.indexPath];
}

Answer 1

@optional annotation asks compiler to avoid generating build warnings, if the class which conforms the protocol has not added the implementation. But, it does not mean that you can execute optional method and not expect a crash.

Use respondsToSelector: to confirm whether the object can respond to the selector or not.

if ([self.delegate respondsToSelector:@selector(textViewDidChange:forIndexPath:)])

In Swift, though, things are simpler. You can use "?" before method call:

delegate?.textViewDidChange?(textView: self.textView, forIndexPath: self.indexPath)

Answer 2

• Its happen if you didn't implement the delegate method on other class but you calling it. To handle crash please use below code

---

- (void)textViewDidChange:(UITextView *)textView
{
    if ([self.delegate respondsToSelector:@selector(textViewDidChange:)]) {
            [self.delegate textViewDidChange:self.textView forIndexPath:self.indexPath];
    }
}