很多时候我们会遇到这样的场景：Xcode停止运行了，我们仍然需要看到我们需要的日志该怎么办？

• 下面方法在- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions；中调用

 - (void)redirectNSLogToDocumentFolder
{
    //如果已经连接Xcode调试则不输出到文件
    if(isatty(STDOUT_FILENO)) {
        return;
    }
    
    UIDevice *device = [UIDevice currentDevice];
    if([[device model] hasSuffix:@"Simulator"]){ //在模拟器不保存到文件中
        return;
    }
    
    //获取Document目录下的Log文件夹，若没有则新建
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *logDirectory = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"Log"];
    
    NSFileManager *fileManager = [NSFileManager defaultManager];
    BOOL fileExists = [fileManager fileExistsAtPath:logDirectory];
    if (!fileExists) {
        [fileManager createDirectoryAtPath:logDirectory  withIntermediateDirectories:YES attributes:nil error:nil];
    }
    
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"zh_CN"]];
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; //每次启动后都保存一个新的日志文件中
    NSString *dateStr = [formatter stringFromDate:[NSDate date]];
    NSString *logFilePath = [logDirectory stringByAppendingFormat:@"/%@.txt",dateStr];
    
    // freopen 重定向输出输出流，将log输入到文件
    freopen([logFilePath cStringUsingEncoding:NSASCIIStringEncoding], "a+", stdout);
    freopen([logFilePath cStringUsingEncoding:NSASCIIStringEncoding], "a+", stderr);
}

• info.plist中添加UIFileSharingEnabled设置为YES 这一步是为了让app通过itunes进行文件共享 这样我们就可以通过itunes获取log日志了

• 连接itunes查看log文件

  
  
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参考文章http://blog.csdn.net/winzlee/article/details/50483424