objective-c - 使用 NSFileHandle 读取/写入文件的示例

Question

是否有使用 objective c 进行文件 block 读/写的好例子？我是 objective-c 和 iPhone API 的新手，这里是我编写的示例代码。有更好的方法吗？

-(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;
    }
}

我在尝试写入时遇到以下异常:

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

Answer 1

需要更改 outputFileHandle 行:

 outputFileHandle  = [NSFileHandle fileHandleForWritingAtPath: self.outputFilePath];