如何捕获异常？

原文：iOS面试题大全

• 在app启动时(didFinishLaunchingWithOptions)，添加一个异常捕获的监听。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    NSSetUncaughtExceptionHandler(&UncaughtExceptionHandler);

    return YES;
}

• 实现捕获异常日志并保存到本地的方法。

void UncaughtExceptionHandler(NSException *exception){
    
    // 异常日志获取
    NSArray  *excpArr = [exception callStackSymbols];
    NSString *reason = [exception reason];
    NSString *name = [exception name];
    
    NSString *excpCnt = [NSString stringWithFormat:@"exceptionType: %@ \n reason: %@ \n stackSymbols: %@",name,reason,excpArr];
    
    // 日常日志保存（可以将此功能单独提炼到一个方法中）
    NSArray  *dirArr  = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *dirPath = dirArr[0];
    NSString *logDir = [dirPath stringByAppendingString:@"/CrashLog"];
    
    BOOL isExistLogDir = YES;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager fileExistsAtPath:logDir]) {
        isExistLogDir = [fileManager createDirectoryAtPath:logDir withIntermediateDirectories:YES attributes:nil error:nil];
    }
    
    if (isExistLogDir) {
        // 此处可扩展
        NSString *logPath = [logDir stringByAppendingString:@"/crashLog.txt"];
        [excpCnt writeToFile:logPath atomically:YES encoding:NSUTF8StringEncoding error:nil];
    }
}