如何防止MFMailComposeViewController的取消崩溃？

Question

某处:

if([MFMailComposeViewController canSendMail])
{
    MFMailComposeViewController *email_vc = [[MFMailComposeViewController alloc] init];
    email_vc.mailComposeDelegate = self;

    [email_vc setSubject:subject];
    [email_vc setMessageBody:message isHTML:FALSE];
    [email_vc setToRecipients:recipients];

    [self presentModalViewController:email_vc animated:FALSE];
    [[UIApplication sharedApplication] setStatusBarHidden:TRUE];
    [email_vc release];
}
else
...

别的地方:

- (void)mailComposeController:(MFMailComposeViewController*)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError*)error
{
    switch (result) 
    {
        case MFMailComposeResultCancelled:
            NSLog(@"Cancelled");
            break;

        case MFMailComposeResultSaved:
            NSLog(@"Saved");
            break;

        case MFMailComposeResultSent:
            NSLog(@"Sent");
            break;

        case MFMailComposeResultFailed:
            NSLog(@"Compose result failed");
            break;

        default:
            NSLog(@"Default: Cancelled");
            break;
    }

    // This ugly thing is required because dismissModalViewControllerAnimated causes a crash
    // if called right away when "Cancel" is touched.

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.01 * NSEC_PER_SEC), dispatch_get_current_queue(), ^
    {
        [self dismissModalViewControllerAnimated:FALSE];
    }); 

}

那个丑陋的"dispatch_after"块是唯一可以让它在没有崩溃的情况下工作的方法.

上下文是在电子邮件撰写视图控制器上触摸"发送"以外的任何内容都将导致崩溃.有没有办法解决这个问题,而不必诉诸这个丑陋的创可贴？我对创可贴的理论是,当您触摸"取消"以确认用户确实要取消时,会显示中间视图.我想知道是否[self dismissModalViewControllerAnimated:FALSE];试图忽视一个不按顺序的视图或那种效果.通过插入一个小延迟,我推断邮件撰写视图有时间清理,然后才会被要求离开.

我看到在另一个问题中使用延迟.但作者没有详细说明:

崩溃在MFMailComposeViewController上为iPad

编辑1:添加崩溃日志

Incident Identifier: ****************
CrashReporter Key:   *****************
Hardware Model:      iPhone4,1
Process:         ************* [9038]
Path:            /var/mobile/Applications/*********************
Identifier:      ***********************
Version:         ??? (???)
Code Type:       ARM (Native)
Parent Process:  launchd [1]

Date/Time:       2012-07-20 11:25:53.704 -0700
OS Version:      iPhone OS 5.0.1 (9A405)
Report Version:  104

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0xa003853a
Crashed Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libobjc.A.dylib                 0x316b9fbc 0x316b6000 + 16316
1   UIKit                           0x350caa9e 0x34f8e000 + 1297054
2   UIKit                           0x34fa6814 0x34f8e000 + 100372
3   UIKit                           0x34fabfb2 0x34f8e000 + 122802
4   QuartzCore                      0x33354ba0 0x33329000 + 179104
5   libdispatch.dylib               0x37896f74 0x37894000 + 12148
6   CoreFoundation                  0x37bac2d6 0x37b20000 + 574166
7   CoreFoundation                  0x37b2f4d6 0x37b20000 + 62678
8   CoreFoundation                  0x37b2f39e 0x37b20000 + 62366
9   GraphicsServices                0x376adfc6 0x376aa000 + 16326
10  UIKit                           0x34fbf73c 0x34f8e000 + 202556
11  *****************               0x00002346 main (main.m:14)
12  *****************               0x00002304 start + 32

编辑2:经过多次刮擦后,看起来这是一个真正的苹果虫.

我下载并运行了MailComposer示例项目:

http://developer.apple.com/library/ios/#samplecode/MailComposer/Introduction/Intro.html

它工作正常.

然后我编辑代码以在呈现和解除邮件组合控制器时删除动画.

[self presentModalViewController:picker animated:FALSE];

和

[self dismissModalViewControllerAnimated:FALSE];

当然,当使用"取消"来关闭电子邮件撰写UI时,它崩溃了.

运行僵尸带来了这个:

-[MFMailComposeController actionSheet:didDismissWithButtonIndex:]: message sent to deallocated instance 0x7479ef0

我想动作表获取了dismiss消息而不是mail compose视图控制器.

如果有人可以确认行为,我会报告错误.

编辑3:Bug报告.

我接受的答案很好地解释了造成这个问题的潜在机制.此外,在回答评论的来回期间,确定了两个额外的解决方案.所有的创可贴,但现在有一些选择.

我还没有检查过,但我怀疑ShareKit也受此错误的影响(如果邮件撰写视图控制器的演示文稿没有动画).

Answer 1

我想动作表获取了dismiss消息而不是mail compose视图控制器.

不完全的.

事件的顺序可能是这样的:

• 行动表调用-actionSheet:clickedButtonAtIndex:其代表(MFMCVC).
  • MFMailComposeViewController调用-mailComposeController:didFinishWithResult:error:其委托(您的VC)
    • 你的VC电话 [self dismissModalViewControllerAnimated:NO]
      • 这导致MFMCVC被释放.由于解雇不是动画,因此不再涉及MFMCVC.它被解除了!
• 操作表调用-actionSheet:didDismissWithButtonIndex:其委托
  • 但它的代表已被解除分配!
    • 所以它崩溃了!

修复将是苹果公司做actionSheet.delegate = nil的-dealloc.

潜在的解决方法

[[self.modalViewController retain] autorelease]
[self dismissModalViewControllerAnimated:NO]

如果您使用ARC,这有点棘手.