Ios7 当我在加载或打开时触发actionsheet时，ios崩溃将出现

在视图上触发操作表确实在ios 6中起作用，但在ios 7中它现在崩溃了。将其移动到ViewWillAppeal没有帮助。在视图出现后，通过单击按钮触发操作表可以正常工作。为什么它现在不能在ios 7中工作

现在加载视图时，建议采用什么方式自动触发操作表

 UIActionSheet *actionSheet;
    NSString* title  = @"update your public profile picture";

    if (![UIImagePickerController isSourceTypeAvailable: UIImagePickerControllerSourceTypeCamera]) {
        actionSheet = [[UIActionSheet alloc] initWithTitle:title delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles: @"Choose Existing Photo",  nil];     
    }
    else {
        actionSheet = [[UIActionSheet alloc] initWithTitle:title delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles:@"Take Photo", @"Choose Existing Photo",  nil];   
    }

    [actionSheet showFromRect:CGRectMake(0, 0, [[UIScreen mainScreen]bounds].size.width, [[UIScreen mainScreen]bounds].size.height) inView:self.view animated:YES];

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崩溃时的错误消息是什么？SIGABORT，当我查看crashalytics日志时，我看到无法显示工作表，因为视图不在窗口中：