iOS 用string生成txt文件，并保存至本地

/**
 param
 string:文件内容
 fileName:文件名
 */
- (void)writeToTXTFileWithString:(NSString *)string fileName:(NSString *)fileName {
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        @synchronized (self) {
            //获取沙盒路径
            NSArray *paths  = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES);
            //获取文件路径
            NSString *fullName = [NSString stringWithFormat:@"%@.txt", fileName];
            NSString *theFilePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:fullName];
            //创建文件管理器
            NSFileManager *fileManager = [NSFileManager defaultManager];
            //如果文件不存在 创建文件
            if(![fileManager fileExistsAtPath:theFilePath]){
                [@"" writeToFile:theFilePath atomically:YES encoding:NSUTF8StringEncoding error:nil];
            }
            NSFileHandle *fileHandle = [NSFileHandle fileHandleForUpdatingAtPath:theFilePath];
            [fileHandle seekToEndOfFile];  //将节点跳到文件的末尾
            NSData* stringData  = [[NSString stringWithFormat:@"%@\n",string] dataUsingEncoding:NSUTF8StringEncoding];
            [fileHandle writeData:stringData]; //追加写入数据
            [fileHandle closeFile];
        }
    });
}