显示操作表导致CGContext无效的上下文错误
我正在使用操作表来显示供用户select的数据列表。 问题是显示使用[self.actionSheet showInView:self.view]; 导致几个CGContext错误。 相同的代码在iOS 6中运行良好。
码：
self.actionSheet = [[UIActionSheet alloc] initWithTitle:nil delegate:nil cancelButtonTitle:nil destructiveButtonTitle:nil otherButtonTitles:nil]; [self.actionSheet setActionSheetStyle:UIActionSheetStyleBlackOpaque]; CGRect tableFrame = CGRectMake(0, 40, 320, 214); self.tableView = [[UITableView alloc] initWithFrame:tableFrame style:UITableViewStylePlain]; self.tableView.dataSource = self; self.tableView.delegate = self; [self.actionSheet addSubview:self.tableView]; UISegmentedControl *closeButton = [[UISegmentedControl alloc] initWithItems:[NSArray arrayWithObject:@"Done"]]; closeButton.momentary = YES; closeButton.frame = CGRectMake(260, 7.0f, 50.0f, 30.0f); closeButton.tintColor = [UIColor redColor]; [closeButton addTarget:self action:@selector(dismissActionSheet:) forControlEvents:UIControlEventValueChanged]; [self.actionSheet addSubview:closeButton]; [self.actionSheet showFromView:self.view]; [UIView beginAnimations:nil context:nil]; [self.actionSheet setBounds:CGRectMake(0, 0, 320, 485)]; [UIView commitAnimations];
错误：
CGContextSetFillColorWithColor: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextSetStrokeColorWithColor: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextSaveGState: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextSetFlatness: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextAddPath: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextDrawPath: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update. CGContextRestoreGState: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.
更新：
将cancelButtonTitle设置为@“”的解决方法会导致以下UI问题：
原始代码来自另一个stackoverflow的答案，请参阅https://stackoverflow.com/a/2074451/654870 。
我相信这里的答案是，UIActionSheet不打算用这种方式，因此可能有这样的副作用。 从Apple ActionSheet文档中 ，“UIActionSheet不是被devise为子类，也不应该将视图添加到其层次结构中”。
虽然这在iOS 6中并没有给我带来任何问题，但iOS 7中的一些内容已经发生了明显的变化，我更倾向于采用另一种方式，而不是尝试去做与文档相矛盾的事情。 请注意，解决方法可能是传递@“”为cancelButtonTitle，而不是零，但这会导致其他UI问题，可能不会被Apple批准。
替代scheme：
- 创build您自己的视图并以模态方式呈现 – 我做了一个简单的示例项目，展示了一种方法来实现此目的。
- https://github.com/gpambrozio/BlockAlertsAnd-ActionSheets（iOS 7尚未更新）
凯尔，使用@“”后还有什么其他的用户界面问题？
我用下面的代码之后，对我来说工作正常。 我不使用tableview，但我使用pickerview作为子视图。
self.startSheet=[[UIActionSheet alloc]initWithTitle:nil delegate:nil cancelButtonTitle:@"" destructiveButtonTitle:nil otherButtonTitles:nil];
这是我在类似的问题上给出的答案，效果很好
self.actionSheet = [[UIActionSheet alloc] initWithTitle:@"" delegate:nil cancelButtonTitle:nil destructiveButtonTitle:nil otherButtonTitles:nil];
但是，如果你没有背景，就会把graphics/绘图搞乱，所以如果你没有背景，只需要添加这个代码就可以给你默认的动作表。
UIView *background = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 44)]; background.backgroundColor = [UIColor colorWithRed:204.0/255.0 green:204.0/255.0 blue:204.0/255.0 alpha:1]; [self.actionSheet addSubview:background];
然后添加任何你想要的自定义操作表。