6.1iOS异常捕捉，日志组件

在开发APP时，我们通常都会需要捕获异常，防止应用程序突然的崩溃，防止给予用户不友好的体验。

Crash分为两种，一种是由EXC_BAD_ACCESS引起的，原因是访问了不属于本进程的内存地址，有可能是访问已被释放的内存；另一种是未被捕获的Objective-C异常（NSException），导致程序向自身发送了SIGABRT信号而崩溃。其实对于未捕获的Objective-C异常，我们是有办法将它记录下来的，如果日志记录得当，能够解决绝大部分崩溃的问题。这里对于UI线程与后台线程分别说明。

1、首先需要在appDelegate中使用InstallUncaughtExceptionHandler()用于监听

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{
InstallUncaughtExceptionHandler();
self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
// Override point for customization after application launch.
self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil] autorelease];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
}

2、添加UncaughtExceptionHandler这个类
iOS SDK提供的函数是NSSetUncaughtExceptionHandler来进行异常处理。但是无法处理内存访问错误、重复释放等错误,因为这些错误发送的SIGNAL。所以需要处理这些SIGNAL

#import <UIKit/UIKit.h>

@interface UncaughtExceptionHandler : NSObject{
BOOL dismissed;
}

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

void InstallUncaughtExceptionHandler(void);

#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)validateAndSaveCriticalApplicationData:(NSException *)exception
{
/**
*  获取异常崩溃信息
*/
NSArray *callStack = [exception callStackSymbols];
NSString *reason = [exception reason];
NSString *name = [exception name];
NSString *content = [NSString stringWithFormat:@"========异常错误报告========\nname:%@\nreason:\n%@\ncallStackSymbols:\n%@",name,reason,[callStack componentsJoinedByString:@"\n"]];

/**
*  把异常崩溃信息发送至开发者邮件
*/
NSMutableString *mailUrl = [NSMutableString string];
[mailUrl appendString:@"mailto:test@qq.com"];
[mailUrl appendString:@"?subject=程序异常崩溃，请配合发送异常报告，谢谢合作！"];
[mailUrl appendFormat:@"&body=%@", content];
// 打开地址
NSString *mailPath = [mailUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:mailPath]];
}

- (void)handleException:(NSException *)exception
{
[self validateAndSaveCriticalApplicationData: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"
@"Debug details follow:\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

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] autorelease]
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];

[[[[UncaughtExceptionHandler alloc] init] autorelease]
performSelectorOnMainThread:@selector(handleException:)
withObject:
[NSException
exceptionWithName:UncaughtExceptionHandlerSignalExceptionName
reason:
[NSString stringWithFormat:
NSLocalizedString(@"Signal %d was raised.", nil),
signal]
userInfo:
[NSDictionary
dictionaryWithObject:[NSNumber numberWithInt:signal]
forKey:UncaughtExceptionHandlerSignalKey]]
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);
}

3 部分情况的崩溃我们是无法避免的，就算是QQ也会有崩溃的时候。因此我们可以在程序崩溃之前做一些“动作”（收集错误信息），以下例子是把捕获到的异常发送至开发者的邮箱。主要体现在以下代码

- (void)validateAndSaveCriticalApplicationData:(NSException *)exception
{
/**
* 获取异常崩溃信息
*/
NSArray *callStack = [exception callStackSymbols];
NSString *reason = [exception reason];
NSString *name = [exception name];
NSString *content = [NSString stringWithFormat:@"========异常错误报告========\nname:%@\nreason:\n%@\ncallStackSymbols:\n%@",name,reason,[callStack componentsJoinedByString:@"\n"]];

/**
* 把异常崩溃信息发送至开发者邮件
*/
NSMutableString *mailUrl = [NSMutableString string];
[mailUrl appendString:@"mailto:test@qq.com"];
[mailUrl appendString:@"?subject=程序异常崩溃，请配合发送异常报告，谢谢合作！"];
[mailUrl appendFormat:@"&body=%@", content];
// 打开地址
NSString *mailPath = [mailUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:mailPath]];
}

- (void)handleException:(NSException *)exception
{
[self validateAndSaveCriticalApplicationData: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"
@"Debug details follow:\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];
}
}

注意：如果在模拟器中运行会产生错误

LaunchServices: ERROR: There is no registered handler for URL scheme mailto
Launch Services是一个应用打开另外应用的服务框架，出现这个错误的原因是，设备或者模拟器没有安装打开该服务的程序。上面的错误是在模拟器中没有打开邮件的设备。