NSFileManager和NSFileHandler的作用， category的理解

/**
 *  读文件
 */
- (void)readFile{
    //1、实例化
    NSFileHandle *readFile = [NSFileHandle fileHandleForReadingAtPath:@"/tmp/Hello.txt"];
    //2、读文件到文件尾部
    NSData *buffer = [readFile readDataToEndOfFile];
    //3、将NSData转换成字符串
    NSString *temp = [[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding];
    //4、关闭文件
    [readFile closeFile];
}

/**
 *  写文件
 */
- (void)writeFile{
    //1、创建写文件处理器
    NSFileHandle *writeFile = [NSFileHandle fileHandleForWritingAtPath:@"/tmp/newFile.txt"];
    //2、将字符串转换成NSData
    NSString *contents = @"hello everyone";
    NSData *buffer = [contents dataUsingEncoding:NSUTF8StringEncoding];
    //3、写NSData
    [writeFile writeData:buffer];
    //4、关闭文件
    [writeFile closeFile];
}