Compiler gives warning on performSelectorOnMainThread:@selector(delegateMethod)

Question

I have an NSOperation that wraps some web service functionality. The NSOperation has a delegate that is to be messaged when the operation is over.

As the NSOperation

Answer 1

Actually on iOS 4 I prefer using NSNotifications and Observers (with Blocks) to perform updates on the mainthread.

- (id)addObserverForName:(NSString *)name object:(id)obj queue:(NSOperationQueue *)queue usingBlock:(void (^)(NSNotification *))block

I wrote down my design here.

Answer 2

performSelectorOnMainThread:withObject:waitUntilDone: method is declared in NSObject class. If your delegate object inherits from NSObject you can declare it as

NSObject<MyDelegateProtocol> *delegate;

So compiler will know that delegate responds to NSObject's methods and won't issue a warning.

Answer 3

1) Declare your delegate's protocol to extend the NSObject protocol in the .h file

@protocol YourDelegateProtocol <NSObject>

2) Cast to NSObject in your call

[(NSObject*)delegate performSelectorOnMainThread:@selector(getDealersIDSuccess:) withObject:result waitUntilDone:YES];

I definitely recommend number (1).

Answer 4

It might be even a better solution not call performSelectorOnMainThread: on a delegate or other protocol implementation. Make it the responsibility of the delegate/receiver to determine if it needs to do things on the main thread.

[delegate performSelector:@selector(delegateAction:)
               withObject:actionData];

Delegate implementation

- (void)delegateAction:(NSData*)actionData
{
    [self performSelectorOnMainThread:@selector(updateUIForAction:)
                           withObject:actionData
                        waitUntilDone:NO];
}

- (void)updateUIForAction:(NSData*)actionData
{
    // Update your UI objects here
}

It might look like more code, but the responsibility is in the right place now