使用NSFileHandle读/写文件的示例

Question

有没有很好的例子可以用objective c对文件进行块读写？我是objective-c和iPhone应用编程接口的新手，下面是我写的示例代码。有没有更好的方法呢？

-(void) performFileOperation
{
    @try {

        NSFileHandle *inputFileHandle;
        NSFileHandle *outputFileHandle;

        //check whether the output file exist, if not create a new one.
        NSFileManager *morphedFileManager;

        outputFileManager = [NSFileManager defaultManager];

        if ([outputFileManager fileExistsAtPath: self.outputFilePath ] == NO)
        {
            NSLog (@"Output file does not exist, creating a new one");
            [outputFileManager createFileAtPath: self.outputFilePath
                                        contents: nil
                                      attributes: nil];
        }

        NSData *inputDataBuffer;

        inputFileHandle = [NSFileHandle fileHandleForReadingAtPath: self.inputFilePath];

        NSAssert( inputFileHandle != nil, @"Failed to open handle for input file" );

        outputFileHandle  = [NSFileHandle fileHandleForReadingAtPath: self.outputFilePath];

        NSAssert( outputFileHandle != nil, @"Failed to open handle for output file" );

        @try{
            // seek to the start of the file
            [inputFileHandle seekToFileOffset: 0];
            [outputFileHandle seekToFileOffset: 0];

            while( (inputDataBuffer = [inputFileHandle readDataOfLength: 1024]) != nil )
            {
                [outputFileHandle writeData: [self.fileWrapper process: inputDataBuffer]];
            }
        }
        @catch (NSException *exception) {
            @throw;
        }
        @finally {
            [inputFileHandle closeFile];
            [outputFileHandle closeFile];
        }        
    }
    @catch (NSException *exception) {
        @throw;
    }
}

在尝试编写代码时，我遇到了以下异常：

Failed to process input buffer ( *** -[NSConcreteFileHandle writeData:]: Bad file descriptor )

Answer 1

需要更改outputFileHandle行：

 outputFileHandle  = [NSFileHandle fileHandleForWritingAtPath: self.outputFilePath];