ios点击屏幕实现退出键盘的功能

- (void)viewDidLoad
{
//设置退出按钮
UIButton *button=[[UIButton alloc]initWithFrame:CGRectMake(0, 0, 320, 640)];//设置button为整个屏幕
[button addTarget:self action:@selector(keyboardBack) forControlEvents:UIControlEventTouchUpInside];//设置button的行为
[self.view addSubview:button];//将button加入到试图中
[self.view sendSubviewToBack:button];//将button推倒UIview背后
[super viewDidLoad];
// Do any additional setup after loading the view.
}

//取消第一响应者
-(void)keyboardBack{
[self.username resignFirstResponder];//username是textField对象
[self.password resignFirstResponder];//password是textField对象
}