我使用下面的代码发送邮件：
MFMailComposeViewController *picker = [[MFMailComposeViewController alloc] init];
picker.mailComposeDelegate = self;
[picker setSubject:@"my title"];
NSMutableString *emailBody = [[NSMutableString alloc] initWithString: @"Hi\n\n"];
[emailBody appendString: @"test"];
[picker setMessageBody:emailBody isHTML:NO];
[self presentModalViewController:picker animated:YES];
[picker release];
[emailBody release];
该代码在旧操作系统版本（Base SDK 5.0，部署目标 4.0）上运行良好。我刚刚升级到 Xcode 4.5，以 iOS 6.0 作为基础 SDK，部署目标仍然是 4.3，并且代码在 5.0、5.1 和 6.0 的模拟器上仍然运行良好。
现在我使用 iOS 4.3.3 将应用程序安装到 iPad。MFMailComposeViewController没有出现，它占用并且应用程序停止工作。我检查了设备日志，它显示：
Incident Identifier: 53CF815B-36FB-4523-8E58-03D80E6BD2D6
CrashReporter Key: e1ce74069fc4d91cdf244ef60282649f2ea4716e
Hardware Model: iPad1,1
Process: MyApp [1018]
Path: /var/mobile/Applications/75088803-4768-4CD6-A561-553F4A182229/MyApp.app/MyApp
Identifier: MyApp
Version: ??? (???)
Code Type: ARM (Native)
Parent Process: launchd [1]
Date/Time: 2012-11-16 14:29:59.959 +0800
OS Version: iPhone OS 4.3.3 (8J3)
Report Version: 104
Exception Type: 00000020
Exception Codes: 0x8badf00d
Highlighted Thread: 0
Application Specific Information:
MyApp[1018] has active assertions beyond permitted time:
{(
<SBProcessAssertion: 0x1fa0dd00> identifier: Suspending process: MyApp[1018] permittedBackgroundDuration: 10.000000 reason: suspend owner pid:30 preventSuspend preventThrottleDownCPU preventThrottleDownUI
)}
Elapsed total CPU time (seconds): 0.770 (user 0.460, system 0.310), 8% CPU
Elapsed application CPU time (seconds): 0.000, 0% CPU
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0:
0 libsystem_kernel.dylib 0x332e5c00 mach_msg_trap + 20
1 libsystem_kernel.dylib 0x332e5758 mach_msg + 44
2 AppSupport 0x33bbb7b8 CPDMTwoWayMessage + 164
3 AppSupport 0x33bba530 -[CPDistributedMessagingCenter _sendMessage:userInfoData:oolKey:oolData:makeServer:receiveReply:nonBlocking:error:] + 352
4 AppSupport 0x33bba0b2 -[CPDistributedMessagingCenter _sendMessage:userInfo:receiveReply:error:toTarget:selector:context:nonBlocking:] + 618
5 AppSupport 0x33bb91ae -[CPDistributedMessagingCenter _sendMessage:userInfo:receiveReply:error:toTarget:selector:context:] + 58
6 AppSupport 0x33bb9312 -[CPDistributedMessagingCenter sendMessageAndReceiveReplyName:userInfo:] + 42
7 MessageUI 0x3693c1fa _CallMessageUIServiceMethod + 182
8 MessageUI 0x3693c01e +[MFMailAccountProxy reloadAccounts] + 22
9 MessageUI 0x3693bf6c +[MFMailComposeController _refreshMailAccountsIfNecessary] + 32
10 MessageUI 0x3693bf2a +[MFMailComposeController isSetupForDelivery] + 10
11 MessageUI 0x3693be80 +[MFMailComposeViewController canSendMail] + 24
12 MessageUI 0x3693bc36 -[MFMailComposeViewController initWithComposition:contentSize:mailComposeControllerOptions:] + 42
13 MessageUI 0x3693bbf8 -[MFMailComposeViewController initWithComposition:] + 28
14 MessageUI 0x36963fac -[MFMailComposeViewController initWithNibName:bundle:] + 44
15 UIKit 0x329e8a0c -[UIViewController init] + 12
16 MyApp 0x000d09ee 0xb5000 + 113134
17 MyApp 0x000e3820 0xb5000 + 190496
18 UIKit 0x32ad1036 -[UIActionSheet(Private) _buttonClicked:] + 186
19 CoreFoundation 0x32dc956a -[NSObject(NSObject) performSelector:withObject:withObject:] + 18
20 UIKit 0x329ceec2 -[UIApplication sendAction:to:from:forEvent:] + 78
21 UIKit 0x329cee62 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
22 UIKit 0x329cee34 -[UIControl sendAction:to:forEvent:] + 32
23 UIKit 0x329ceb86 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 350
24 UIKit 0x329cf41c -[UIControl touchesEnded:withEvent:] + 336
25 UIKit 0x329cdbee -[UIWindow _sendTouchesForEvent:] + 362
26 UIKit 0x329cd568 -[UIWindow sendEvent:] + 256
27 UIKit 0x329b630c -[UIApplication sendEvent:] + 292
28 UIKit 0x329b5c4c _UIApplicationHandleEvent + 5084
29 GraphicsServices 0x35c8ee70 PurpleEventCallback + 660
30 CoreFoundation 0x32e30a90 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 20
31 CoreFoundation 0x32e32838 __CFRunLoopDoSource1 + 160
32 CoreFoundation 0x32e33606 __CFRunLoopRun + 514
33 CoreFoundation 0x32dc3ebc CFRunLoopRunSpecific + 224
34 CoreFoundation 0x32dc3dc4 CFRunLoopRunInMode + 52
35 GraphicsServices 0x35c8e418 GSEventRunModal + 108
36 GraphicsServices 0x35c8e4c4 GSEventRun + 56
37 UIKit 0x329e0d62 -[UIApplication _run] + 398
38 UIKit 0x329de800 UIApplicationMain + 664
39 MyApp 0x000c95a4 0xb5000 + 83364
40 MyApp 0x000b73b8 0xb5000 + 9144
Thread 1 name: Dispatch queue: com.apple.libdispatch-manager
Thread 1:
0 libsystem_kernel.dylib 0x332e8fbc kevent + 24
1 libdispatch.dylib 0x33abc032 _dispatch_mgr_invoke + 706
2 libdispatch.dylib 0x33abd03a _dispatch_queue_invoke + 86
3 libdispatch.dylib 0x33abc5ea _dispatch_worker_thread2 + 186
4 libsystem_c.dylib 0x363d958a _pthread_wqthread + 258
5 libsystem_c.dylib 0x363d9bbc start_wqthread + 0
Thread 2 name: WebThread
Thread 2:
0 libsystem_kernel.dylib 0x332e5c00 mach_msg_trap + 20
1 libsystem_kernel.dylib 0x332e5758 mach_msg + 44
2 CoreFoundation 0x32e312b8 __CFRunLoopServiceMachPort + 88
3 CoreFoundation 0x32e33562 __CFRunLoopRun + 350
4 CoreFoundation 0x32dc3ebc CFRunLoopRunSpecific + 224
5 CoreFoundation 0x32dc3dc4 CFRunLoopRunInMode + 52
6 WebCore 0x31e5c27e RunWebThread(void*) + 382
7 libsystem_c.dylib 0x363d830a _pthread_start + 242
8 libsystem_c.dylib 0x363d9bb4 thread_start + 0
欢迎任何评论。