【iOS】通知监听

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    // 1.监听通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextFieldTextDidChangeNotification object:self.accountField];
}
//监听结束需要移除
- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

/**
 *  文本框的文字发生改变的时候调用
 */
- (void)textChange
{
    self.loginBtn.enabled = (self.accountField.text.length && self.pwdField.text.length);
}