使用initWithFrame生成的UIView，backgroundColor默认的opaque是0

如标题，使用initWithFrame生成的UIView，backgroundColor默认的opaque是0，若不修改这个opaque，其无法接收到各种gesture，测试代码如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    CGRect rectScr=[UIScreenmainScreen].bounds;

    UIWindow *window=[[UIWindowalloc] initWithFrame:rectScr];

    UIViewController *vc=[[UIViewControlleralloc] init];

    myView *view=[[myViewalloc] initWithFrame:rectScr];  //myView类继承了UIView类，且自带了UITapGestureRecognizer的响应函数

    view.backgroundColor=[UIColorcolorWithRed:0green:0.3blue:0alpha:1];  //一定要带上这句，否则默认的 alpha是0，代表view是透明的，本view接收不到手势事件

    vc.view=view;

    window.rootViewController=vc;

    self.window=window;

    returnYES;

}