Question

I’m fairly new to Objective-C, and it would be really helpful if someone could help me with the following task:

I have a class TheController that has a method DoTask. The goal of DoTask is to reach out to a MasterUtility (also a custom made class) and get Data, and then send it back when it is done (it uses a thread). Specifically, I want it to send it to dataReceiver in ReportsViewController. I think I need to use @selector or something like that. Here is some code:

@implementation ReportsViewController

-(void)doTask {
     MasterUtilities *mu = [[MasterUtilities alloc] init];
     [mu getDataAndSendTo:[WHAT GOES HERE]]
}

-(void)dataReceiver:(NSArray *)data {
    NSLog(@"data: %@",data);
}

@end

Here is MasterUtilities

    @implementation MasterUtilities

   - (void)getDataAndSendTo:[WHAT GOES HERE] {
        NSArray *data = [[NSArray init] alloc];
        ....getting data here....

        [WHAT GOES HERE? HOW DO I CALL THE METHOD (dataReceiver) IN ReportsViewController?]
     }

     @end

Can anyone fill in the areas that indicate “WHAT GOES HERE”? Thank you!!

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Answer 1

You could use a block:

typedef void (^Callback)(NSArray*);

[somebody doSomethingAndPerform:^(NSArray *data) {
    // do whatever you want with the data
}];

- (void) doSomethingAndPerform: (Callback) callback
{
    NSArray *data = …;
    callback(data);
}

This is very flexible, but maybe too complex. If you want something simpler, you can always just pass the selector and target, just as you thought:

[somebody doSomethingAndCall:@selector(dataReceiver:) on:self];

- (void) doSomethingAndCall: (SEL) selector on: (id) target
{
    NSArray *data = …;
    [target performSelector:selector withObject:data];
}

Or you can use a protocol:

@protocol DataConsumer
- (void) handleData: (NSArray*) data;
@end

// this class has to implement DataConsumer
[somebody doSomethingAndNotify:self];

- (void) doSomethingAndNotify: (id <DataConsumer>) consumer
{
    NSArray *data = …;
    [consumer handleData:data];
}

This solution is a bit heawyweight, but the advantage is that the compiler catches some errors for you. There’s also more coupling, but it’s far from being a problem.