UIActionSheet警告，提示调用showFromTabBar方法

    UIActionSheet *actionSheet = [[UIActionSheet alloc]initWithTitle:@"选择图片" delegate:(self) cancelButtonTitle:@"取消" destructiveButtonTitle:nil otherButtonTitles:@"拍照",@"从手机相册选择", nil];
    actionSheet.actionSheetStyle = UIActionSheetStyleBlackOpaque;
    [actionSheet showFromTabBar:self.tabBarController.tabBar];