Question

My app gets some json data from a server and it uses a NSMUtableData object to store these data.
But debugger is reporting the following error:

[NSCFString setLength:]: unrecognized selector sent to instance

and the debugger highlighted the following line (in connection didReceiveResponse method):

[rqst_data setLength:0];

rqst_data is declared as NSMutableData in header file.

Thx in advance for your kind help,

Stephane

Answer 1

It seems your rqst_data variable gets released. Make sure you have properly allocated it. If you have declared @property for it you better use the variable as self.rqst_data.
You can use retain and in case of IOS 5 strong in property declaration.

You can track if any variable gets released via setting NSZombieEnabled to YES. With zombies enabled, messages to deallocated objects will no longer behave strangely or crash in difficult-to-understand ways, but will instead log a message and die in a predictable and debugger-breakpointable way.
You can set NSZombieEnabled by the following steps.

Select Product from the menu bar above. Keep alt/option pressed and select “Test…” or “Run…”.

1.
Go to the Arguments tab, and add NSZombieEnabled YES in the “Environment Variables” section.

OR

2.
Go to the Diagnostics tab, and check Enable Zombie Objects in the “Memory Management” section.