讓 iOS App 優雅的 Crash 吧！

開發 iOS App 最害怕的一件事就屬上架審核了！

不僅要讓 Apple 恣意的玩弄 App 所有的功能以外，更令人尷尬的事情是 － Bug 總會在這時候爭先恐後的冒出來，造成 crash reject（註1：教育訓練定理）。

如果剛好這些 Bug 們生性害羞靦腆，躲過了審查而順利的上架了，這時候卻換成使用者三不五時反應說程式一直當機，一直閃退（註2：使用者天生是讓系統崩潰的天才），但是你卻想破頭也不知道原因是什麼，這時候如果有個能將當下的錯誤訊息回報給你，至少有個方向可以去追查。

註1：教育訓練定理。教育訓練等正式場合，系統的 Bug 就有如脫韁的野馬一般，總在令人意想不到的情形下大肆奔放。
註2：使用者天生是讓系統崩潰的天才。不解釋......

今天要介紹的是，如何讓 App 崩潰的時候，能夠崩的優雅，崩的面不改色，崩的理所當然。



首先要了解的是，一般在 iOS 中系統遇到了 Exception 時，我們可以用 try...catch 來捕捉這些例外情況，但是會造成 App 直接 crash 的狀況時，不論再怎麼包 try...catch 就是無法將錯誤例外抓出來，這是因為系統對於這一類的錯誤不是拋出 Exception 訊息，而是 Signal 訊號。

所以如果想要捕捉這些錯誤例外，就必須自己手動捕捉。

UncaughtExceptionHandler.h

#import <Foundation/Foundation.h>
#import <MessageUI/MFMailComposeViewController.h>

@interface UncaughtExceptionHandler : NSObject <MFMailComposeViewControllerDelegate>
{
 BOOL dismissed;
}

@end
void HandleException( NSException *exception);
void SignalHandler( int signal);
void InstallUncaughtExceptionHandler( void );

UncaughtExceptionHandler.m

#import "UncaughtExceptionHandler.h"
#include <libkern/OSAtomic.h>
#include <execinfo.h>
#import <MessageUI/MFMailComposeViewController.h>
#import "AppDelegate.h"

NSString * const UncaughtExceptionHandlerSignalExceptionName = @ "UncaughtExceptionHandlerSignalExceptionName" ;
NSString * const UncaughtExceptionHandlerSignalKey = @ "UncaughtExceptionHandlerSignalKey" ;
NSString * const UncaughtExceptionHandlerAddressesKey = @ "UncaughtExceptionHandlerAddressesKey" ;

volatile int32_t UncaughtExceptionCount = 0;
const int32_t UncaughtExceptionMaximum = 10;

const NSInteger UncaughtExceptionHandlerSkipAddressCount = 4;
const NSInteger UncaughtExceptionHandlerReportAddressCount = 5;

@implementation UncaughtExceptionHandler

+ ( NSArray *)backtrace
{
 void * callstack[128];
 int frames = backtrace(callstack, 128);
 char **strs = backtrace_symbols(callstack, frames);

 NSMutableArray *backtrace = [ NSMutableArray arrayWithCapacity:frames];
 for ( int i = UncaughtExceptionHandlerSkipAddressCount;
  i < UncaughtExceptionHandlerSkipAddressCount + UncaughtExceptionHandlerReportAddressCount;
  i++)
 {
  [backtrace addObject:[ NSString stringWithUTF8String:strs[i]]];
 }
 free(strs);

 return backtrace;
}

- ( void )alertView:(UIAlertView *)anAlertView clickedButtonAtIndex:( NSInteger )anIndex
{
 if (anIndex == 0)
 {
  dismissed = YES ;
 }
 else if (anIndex == 1)
 {
  NSBundle *bundle = [ NSBundle mainBundle];
  NSDictionary *info = [bundle infoDictionary];
  NSString *productName = [info objectForKey:@ "CFBundleDisplayName" ];

  // 開啟寄信的 view
  MFMailComposeViewController *mailView = [[MFMailComposeViewController alloc] init];
  mailView.mailComposeDelegate = self ;
  [mailView setEditing: NO animated: YES ];
  [mailView setEditing: NO ];
  [mailView setToRecipients:@[@ "[email protected]" ]];
  [mailView setSubject:[ NSString stringWithFormat:@ "[%@] - 錯誤回報" ,productName]];
  [mailView setMessageBody:anAlertView.message isHTML: NO ];

  if (mailView)
  {
   AppDelegate *appDelegate = (AppDelegate*)[UIApplication sharedApplication].delegate;
   [appDelegate.window.rootViewController presentViewController:mailView animated: YES completion:^{}];
  }
 }
}

- ( void )validateAndSaveCriticalApplicationData
{

}

-( void )mailComposeController:(MFMailComposeViewController *)controller didFinishWithResult:(MFMailComposeResult)result error:( NSError *)error
{
 if (result == MFMailComposeResultSent)
 {

 }

 AppDelegate *appDelegate = (AppDelegate*)[UIApplication sharedApplication].delegate;
 [appDelegate.window.rootViewController dismissViewControllerAnimated: YES completion:^{}];
}

- ( void )handleException:( NSException *)exception
{
    [ self validateAndSaveCriticalApplicationData];

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@ "喔喔！程式發生了異常！"
              message:[ NSString stringWithFormat:@ "為了讓 App 可以更好，請將錯誤訊息回報給開發人員！\n\n" @ "異常原因如下:\n%@\n%@" ,exception.reason,[exception.userInfo objectForKey:UncaughtExceptionHandlerAddressesKey]]
             delegate: self
             cancelButtonTitle:@ "退出"
             otherButtonTitles:@ "回報" , nil ];
 [alert show];

 CFRunLoopRef runLoop = CFRunLoopGetCurrent();
 CFArrayRef allModes = CFRunLoopCopyAllModes(runLoop);

 while (!dismissed)
 {
  for ( NSString *mode in (__bridge NSArray *)allModes)
  {
   // 0.1 是 run loop 的時間，越短畫面捕捉使用者觸碰反應越靈敏，但是會讓 cpu 非常忙碌，結果就造成凍結。
   CFRunLoopRunInMode((__bridge CFStringRef)mode, 0.1, false );
  }
 }

 CFRelease(allModes);

 NSSetUncaughtExceptionHandler ( NULL );
 signal(SIGABRT, SIG_DFL);
 signal(SIGILL, SIG_DFL);
 signal(SIGSEGV, SIG_DFL);
 signal(SIGFPE, SIG_DFL);
 signal(SIGBUS, SIG_DFL);
 signal(SIGPIPE, SIG_DFL);

 if ([exception.name isEqual:UncaughtExceptionHandlerSignalExceptionName])
 {
  kill(getpid(), [[exception.userInfo objectForKey:UncaughtExceptionHandlerSignalKey] intValue]);
 }
 else
 {
  //[exception raise];
  exit(0);
 }
}

@end

void HandleException( NSException *exception)
{
 int32_t exceptionCount = OSAtomicIncrement32(&UncaughtExceptionCount);
 if (exceptionCount > UncaughtExceptionMaximum)
 {
  return ;
 }

 NSArray *callStack = [UncaughtExceptionHandler backtrace];
 NSMutableDictionary *userInfo = [ NSMutableDictionary dictionaryWithDictionary:exception.userInfo];
 [userInfo setObject:callStack forKey:UncaughtExceptionHandlerAddressesKey];

 [[[UncaughtExceptionHandler alloc] init] performSelectorOnMainThread: @selector (handleException:)
                 withObject:[ NSException exceptionWithName:exception.name
                         reason:exception.reason
                          userInfo:userInfo]
                 waitUntilDone: YES ];
}

void SignalHandler( int signal)
{
 int32_t exceptionCount = OSAtomicIncrement32(&UncaughtExceptionCount);
 if (exceptionCount > UncaughtExceptionMaximum)
 {
  return ;
 }

 NSMutableDictionary *userInfo = [ NSMutableDictionary dictionaryWithObject:[ NSNumber numberWithInt:signal]
                    forKey:UncaughtExceptionHandlerSignalKey];

 NSArray *callStack = [UncaughtExceptionHandler backtrace];
 [userInfo setObject:callStack forKey:UncaughtExceptionHandlerAddressesKey];
 NSException *exception = [ NSException exceptionWithName:UncaughtExceptionHandlerSignalExceptionName
              reason:[ NSString stringWithFormat:@ "Signal %d 被觸發" ,signal]
               userInfo:[ NSDictionary dictionaryWithObject:[ NSNumber numberWithInt:signal]
                      forKey:UncaughtExceptionHandlerSignalKey]];

 [[[UncaughtExceptionHandler alloc] init] performSelectorOnMainThread: @selector (handleException:)
                 withObject:exception
                 waitUntilDone: YES ];
}

void InstallUncaughtExceptionHandler( void )
{
 NSSetUncaughtExceptionHandler (&HandleException);
 signal(SIGABRT, SignalHandler);
 signal(SIGILL, SignalHandler);
 signal(SIGSEGV, SignalHandler);
 signal(SIGFPE, SignalHandler);
 signal(SIGBUS, SignalHandler);
 signal(SIGPIPE, SignalHandler);
}

完成了之後，在 AppDelegate.m中

- ( BOOL )application:(UIApplication *)application didFinishLaunchingWithOptions:( NSDictionary *)launchOptions
{
 InstallUncaughtExceptionHandler();

 self .window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
 self .window.backgroundColor = [UIColor whiteColor];
 self .window.rootViewController = [[MainViewController alloc] init];

 [ self .window makeKeyAndVisible];
    return YES ;
}

這樣就完成了捕捉了，以下是測試效果

可喜可賀！可喜可賀！

範例檔下載： ElegantDeath.zip