雖然大家都不願意看到程序崩潰，但可能崩潰是每個應用必須面對的現實，既然崩潰已經發生，無法阻擋了，那我們就讓它崩也崩得淡定點吧。
IOS SDK中提供了一個現成的函數 NSSetUncaughtExceptionHandler 用來做異常處理，但功能非常有限，而引起崩潰的大多數原因如：內存訪問錯誤，重複釋放等錯誤就無能爲力了，因爲這種錯誤它拋出的是Signal，所以必須要專門做Signal處理。首先定義一個UncaughtExceptionHandler類，.h頭文件的代碼如下：
#import <UIKit/UIKit.h>
@interface UncaughtExceptionHandler : NSObject
{
BOOL dismissed;
}
@end
void InstallUncaughtExceptionHandler();
然後在.mm文件實現InstallUncaughtExceptionHandler()，如下：
void InstallUncaughtExceptionHandler()
{
signal(SIGABRT, MySignalHandler);
signal(SIGILL, MySignalHandler);
signal(SIGSEGV, MySignalHandler);
signal(SIGFPE, MySignalHandler);
signal(SIGBUS, MySignalHandler);
signal(SIGPIPE, MySignalHandler);
}
這樣，當應用發生錯誤而產生上述Signal後，就將會進入我們自定義的回調函數MySignalHandler。爲了得到崩潰時的現場信息，還可以加入一些獲取CallTrace及設備信息的代碼，.mm文件的完整代碼如下：
#import "UncaughtExceptionHandler.h"
#include <libkern/OSAtomic.h>
#include <execinfo.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);
int i;
NSMutableArray *backtrace = [NSMutableArray arrayWithCapacity:frames];
for (
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;
}
}
- (void)handleException:(NSException *)exception
{
UIAlertView *alert =
[[[UIAlertView alloc]
initWithTitle:NSLocalizedString(@"Unhandled exception", nil)
message:[NSString stringWithFormat:NSLocalizedString(
@"You can try to continue but the application may be unstable.\n"
@"%@\n%@", nil),
[exception reason],
[[exception userInfo] objectForKey:UncaughtExceptionHandlerAddressesKey]]
delegate:self
cancelButtonTitle:NSLocalizedString(@"Quit", nil)
otherButtonTitles:NSLocalizedString(@"Continue", nil), nil]
autorelease];
[alert show];
CFRunLoopRef runLoop = CFRunLoopGetCurrent();
CFArrayRef allModes = CFRunLoopCopyAllModes(runLoop);
while (!dismissed)
{
for (NSString *mode in (NSArray *)allModes)
{
CFRunLoopRunInMode((CFStringRef)mode, 0.001, 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];
}
}
@end
NSString* getAppInfo()
{
NSString *appInfo = [NSString stringWithFormat:@"App : %@ %@(%@)\nDevice : %@\nOS Version : %@ %@\nUDID : %@\n",
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleDisplayName"],
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"],
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"],
[UIDevice currentDevice].model,
[UIDevice currentDevice].systemName,
[UIDevice currentDevice].systemVersion,
[UIDevice currentDevice].uniqueIdentifier];
NSLog(@"Crash!!!! %@", appInfo);
return appInfo;
}
void MySignalHandler(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];
[[[[UncaughtExceptionHandler alloc] init] autorelease]
performSelectorOnMainThread:@selector(handleException:)
withObject:
[NSException
exceptionWithName:UncaughtExceptionHandlerSignalExceptionName
reason:
[NSString stringWithFormat:
NSLocalizedString(@"Signal %d was raised.\n"
@"%@", nil),
signal, getAppInfo()]
userInfo:
[NSDictionary
dictionaryWithObject:[NSNumber numberWithInt:signal]
forKey:UncaughtExceptionHandlerSignalKey]]
waitUntilDone:YES];
}
void InstallUncaughtExceptionHandler()
{
signal(SIGABRT, MySignalHandler);
signal(SIGILL, MySignalHandler);
signal(SIGSEGV, MySignalHandler);
signal(SIGFPE, MySignalHandler);
signal(SIGBUS, MySignalHandler);
signal(SIGPIPE, MySignalHandler);
}
在應用自身的 didFinishLaunchingWithOptions 前，加入一個函數：
- (void)installUncaughtExceptionHandler
{
InstallUncaughtExceptionHandler();
}
最後，在 didFinishLaunchingWithOptions 中加入這一句代碼就行了：
[self InstallUncaughtExceptionHandler];
現在，基本上所有崩潰都能Hold住了。崩潰時將會顯示出如下的對話框：
這樣在崩潰時還能從容地彈出對話框，比起閃退來，用戶也不會覺得那麼不爽。然後在下次啓動時還可以通過郵件來發送Crash文件到郵箱，這就看各個應用的需求了。
