监听TextField文本值 实现按钮enable值的改变

在这里使用addTarget比较好

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self.nameField addTarget:self action:@selector(textValueChanged) forControlEvents:UIControlEventEditingChanged];
    [self.phoneField addTarget:self action:@selector(textValueChanged) forControlEvents:UIControlEventEditingChanged];
}

/**
 *  监听文本输入框内容的改变
 */
- (void)textValueChanged{
    self.addBtn.enabled = (self.nameField.text.length != 0 && self.phoneField.text.length != 0);
}

UIControlEventEditingChanged是重点，不要写成了UIControlEventValueChanged