//把bgView强制修改成UIControl,以便响应触摸事件
//UIControl是UIView的子类
//其实有很多情况都可以这样用，用一个普通的UIView来模拟某些控件，可以很灵活！！！！
UIView *bgView;
CGRect bgFrame = CGRectMake(0.0, 35.0, 320.0, 460.0 - 35.0);
UIControl *bgControl = [[UIControl alloc] initWithFrame:bgFrame];
[bgControl addTarget:self
action:@selector(resignKeyboardAction)
forControlEvents:UIControlEventTouchDown];
self.bgView = bgControl;
[bgControl release];
self.bgView.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.5];
self.bgView.hidden = YES;
[self.view addSubview:bgView];