解决Sheet can not be presented because the view is not in a window这样的问题

IOS7下使用actionsheet时，有时会遇见这样的报错：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Sheet can not be presented because the view is not in a window: >'

*** First throw call stack:

这种情况，是因为视图并未在窗口加载，那么我们把actionsheet加载在当前window中就可以了。

兼容IOS6下的情况，代码如下：

//解决“Sheet can not be presented because the view is not in a window” 这样的问题
    UIWindow* window = [[UIApplication sharedApplication] keyWindow];
    if ([window.subviews containsObject:self.view]) {
        [actionSheet showInView:self.view];
    } else {
        [actionSheet showInView:window];
    }