Objective-C监听键盘删除按钮

响应键盘删除按钮的事件，常规的是根据UITextfield或者UISearchBar的didChange代理方法中内同的改变来判断是否进行了点击删除按钮。但是当输入框没有内容时，就无法捕捉到删除的事件了。例如微信选择好友时用键盘的删除按钮删除已选择的好友头像。

实现的思路是利用OC的运行时机制，替换掉系统的删除runtime函数。首先建一个UItextfield的category：UITextField+YX

头文件代码：

#import <UIKit/UIKit.h>
@protocol YXTextFieldDelegate <UITextFieldDelegate>
@optional
- (void)textFieldDidDeleteBackward:(UITextField *)textField;
@end
@interface UITextField (YX)
@property (weak, nonatomic) id<YXTextFieldDelegate> delegate;
@end
/**
*  监听删除按钮
*  object:UITextField
*/
extern NSString * const YXTextFieldDidDeleteBackwardNotification;

源文件中的代码：

#import "UITextField+YX.h"
#import <objc/runtime.h>

NSString * const YXTextFieldDidDeleteBackwardNotification = @"textfield_did_notification";

@implementation UITextField(YX)

+ (void)load {
Method method1 = class_getInstanceMethod([self class], NSSelectorFromString(@"deleteBackward"));
Method method2 = class_getInstanceMethod([self class], @selector(yx_deleteBackward));
method_exchangeImplementations(method1, method2);
}

- (void)yx_deleteBackward {
[self yx_deleteBackward];

if ([self.delegate respondsToSelector:@selector(textFieldDidDeleteBackward:)])
{
id <YXTextFieldDelegate> delegate  = (id<YXTextFieldDelegate>)self.delegate;
[delegate textFieldDidDeleteBackward:self];
}

[[NSNotificationCenter defaultCenter] postNotificationName:YXTextFieldDidDeleteBackwardNotification object:self];
}

@end

在使用的文件中遵循YXTextFieldDelegate代理，代理的方法即为点击删除按钮事件：

- (void)textFieldDidDeleteBackward:(UITextField *)textField {
//删除事件
}

github:监听键盘删除按钮，仿微信好友选择