How does NSMutableData work?

Question

I have one problem to work with NSMutableData.

I defined one NSMutableData *receivedData, and tried to copy several NSData* data to the receivedData. I just called [receivedData appendData:data], but appears the data is not copied:

....
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

Thanks.

Solution

Check if receivedData == nil. If so, then you might have forgotten to initialize it. For example:

receivedData = [[NSMutableData alloc] init];

Then release it when you don't need it anymore:

[receivedData release];
receivedData = nil;

Comments

[BlueDolphin]

Yes, that's the problem. Originally I thought if it is nil, it will report error. Thanks so much.

[Abizern]

In Objective-C it is legal to send messages to nil, so no error there.