UITextField 监听数值变化的三种方法

1.直接监听 - 推荐

#pragma mark - 直接添加监听方法
-(void)addTargetMethod{
    [self.textField1 addTarget:self action:@selector(textField1TextChange:) forControlEvents:UIControlEventEditingChanged];
}
-(void)textField1TextChange:(UITextField *)textField{
    NSLog(@"textField1 - 输入框内容改变,当前内容为: %@",textField.text);
}

2.NSNotificationCenter 添加监听方法

#pragma mark - NSNotificationCenter 添加监听方法
-(void)addNSNotificationCenter{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textField2TextChange:) name:UITextFieldTextDidChangeNotification object:self.textField2];
}
-(void)textField2TextChange:(NSNotification *)noti{
    UITextField *currentTextField = (UITextField *)noti.object;
    NSLog(@"textField2 - 输入框内容改变,当前内容为: %@",currentTextField.text);
}
-(void)dealloc{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

3.KVO : 注意这种方法不会直接监听键盘输入而是监听 textField.text 的改变,代码设置才会有效

-(void)addKVO{
    [self.textField3 addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
    self.textField3.text = @"123";
}
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionaryid> *)change context:(void *)context{
    if ([keyPath isEqualToString:@"text"] && object == self.textField3) {
        NSLog(@"textField3 - 输入框内容改变,当前内容为: %@",self.textField3.text);
    }else{
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}
-(void)dealloc{
    [self.textField3 removeObserver:self forKeyPath:@"text" context:nil];
}

4.代理
可以判断接下来是否允许继续输入

#pragma mark - 代理
-(void)addDelegate{
    //实现 UITextFieldDelegate 协议
    self.textField4.delegate = self;
}
#pragma mark  UITextFieldDelegate
- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField{
    return YES;
}// return NO to disallow editing.
- (void)textFieldDidBeginEditing:(UITextField *)textField{
    NSLog(@"textField4 - 开始编辑");
}// became first responder
- (BOOL)textFieldShouldEndEditing:(UITextField *)textField{
    return YES;
}// return YES to allow editing to stop and to resign first responder status. NO to disallow the editing session to end
- (void)textFieldDidEndEditing:(UITextField *)textField{
    NSLog(@"textField4 - 结束编辑");
}// may be called if forced even if shouldEndEditing returns NO (e.g. view removed from window) or endEditing:YES called
- (void)textFieldDidEndEditing:(UITextField *)textField reason:(UITextFieldDidEndEditingReason)reason NS_AVAILABLE_IOS(10_0){

}// if implemented, called in place of textFieldDidEndEditing:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
     NSLog(@"textField4 - 正在编辑, 当前输入框内容为: %@",textField.text);
    return YES;
}// return NO to not change text

项目完整代码:https://git.oschina.net/qxuewei/TextFieldKVOTest