一个UIButton控件的状态设置和事件的执行
[btnCountDown setTitle:@"重新发送短信" forState:UIControlStateDisabled];//禁用的状态显示,这个状态下的btn按钮是不可以监听事件的
//下面的btn按钮是可以监听事件的
[btnCountDown setTitle:@"发送验证码" forState:UIControlStateNormal];
[btnCountDown setTitle:@"发送验证码" forState:UIControlStateHighlighted];
[btnCountDown setTitle:@"发送验证码" forState:UIControlStateDisabled];
btnCountDown.enabled = YES;