problem with nil and release?

i am using NSArray named as allAvailableServices . first i initialize it and after wrote [allAvailableServices release]; then i checked the condition if(al开发者_运维技巧lAvailableServices). it came as true!may i know the reason. then i wrote allAvailableServices = nil; and [allAvailableServices release]; after the above code if(allAvailableServices) came false.is there any problem that i wrote [allAvailableServices release]; after allAvailableServices = nil;

whenever allAvailableServices = nil i need to allocate new array.so if i didn't call [allAvailableServices release]; i think there is a memory problem.am i correct? can any one provide me a best way to deal with it?

Release just reclaims the memory, but the pointer value isn't changed; it still contains a value, but it points to garbage.

This is why many people nil their pointer after releasing it:

[allAvailableServices release], allAvailableServices = nil;

In Objective-C, it is safe to send a message to nil, but sending a message to an object that has been released may cause the app to crash (usually with EXC_BAD_ACCESS)

Note, that I've released the object before setting it to nil. If you do it the other way around, you've lost the pointer to which you send the release message, and so you've leaked the object.

If you use accessors then you can directly set the values to nil, it calls the release and sets them to nil. A release decrements the reference count by 1 and if it reaches 0 the object is freed.

The memory still has some value if you do not set to nil and hence the problem in your if condition.

Cleaner way is to use accessors and call self.yourvariable = nil; .