动态实时监听文本框中内容的变化

@property (strong, nonatomic) UITextField *iPhoneText;

@property (strong, nonatomic) UITextField *passwordText;

@property (strong, nonatomic) UIButton *passwordBtn;

viewdidLoad 中设置文本框的监听变化的方法

　　[self.iPhoneText addTarget:self action:@selector(textChange) forControlEvents:  UIControlEventEditingChanged];

[self.passwordText addTarget:self action:@selector(textChange) forControlEvents:UIControlEventEditingChanged];

[self textChange];

///根据判断 text1与 text2是否有值

-(void)textChange{

self.loginBtn.enabled = self.iPhoneText.text.length && self.passwordText.text.length;

[self.loginBtn setBackgroundColor:LoginButtonColor];

}