NSMutableData如何工作？

我有一个问题需要处理NSMutableData.

我定义了一个NSMutableData *receivedData,并试图将几个NSData*数据复制到receivedData.我刚刚调用[receivedData appendData:data],但似乎没有复制数据:

....
NSLog(@"get data! Received %d bytes of data",[data length]);
  // output is not zero, say 1231.

[receivedData appendData:data];
NSLog(@"after append! length is %d bytes of data",[receivedData length]);
  // showing zero

谢谢.

检查是否receivedData == nil.如果是这样,那么您可能忘记初始化它.例如:

receivedData = [[NSMutableData alloc] init];

然后在您不再需要它时释放它:

[receivedData release];
receivedData = nil;