Do you need to release NSData?

-(void) func1: (NSData*) somedata
{
    //Processing somedata ..开发者_如何学C..

    [somedata release]; //is it necessay? 
}

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You shouldnt release somedata inside your method.

NSData *somedata = [[NSData alloc] init];
func1(somedata);
[somedata release];

Assumptions:

• func1 runs on same thread

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In this case, no, you should not release your object. You're not the "owner". As a rule of thumb, you need to release an object once you're done with it only if:

• You allocated it via [MyClass alloc], as in [[MyClass alloc] init] or [[MyClass alloc] initWithFoo:foo bar:baz].
• You got a copy via [someObject copy] or [someObject mutableCopy].
• You have retained it before.

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You should consider releasing it If you are retaining it in this case. But I am not sure because your question does not provide any idea whether a release is required or not. But generally you will release objects if you take ownership of it.