UIAlertController 实现kvo实现mes文字设置

 UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"更新提示" message:[NSString stringWithFormat:@"%@",self.model.groups.update_content]  preferredStyle: UIAlertControllerStyleAlert];

             UIView *subView1 = alert.view.subviews[];
             UIView *subView2 = subView1.subviews[];
             UIView *subView3 = subView2.subviews[];
             UIView *subView4 = subView3.subviews[];
             UIView *subView5 = subView4.subviews[];
             NSLog(@"%@",subView5.subviews);
             //取title和message：
             //UILabel *title = subView5.subviews[0];
             UILabel *message = subView5.subviews[];
             message.textAlignment = NSTextAlignmentLeft;

             [alert addAction:[UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

             }]];

             [alert addAction:[UIAlertAction actionWithTitle:@"去更新" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                 //点击按钮的响应事件；
                 NSURL *url = [NSURL URLWithString:@"http://itunes.apple.com/cn/app/id1198896188?mt=8"];

                 [[UIApplication sharedApplication]openURL:url];
             }]];

             //弹出提示框；
             [self presentViewController:alert animated:true completion:nil];