ASIHTTPRequest: Results are not populated at the right time when using an asynchronous request

Question

Hello all,

I've my own class which should do the request and the data processing (parsing). This class should be used from different view controllers. In this class I have implemented:

- (void)sendRequest:(NSString *)url;
- (void)requestFinished:(ASIHTTPRequest *)request;
- (void)requestFailed:(ASIHTTPRequest *)request;
- (id)parse:(NSString *)aString;

I have created a property called result. If the request arrives, requestFinished is called. In requestFinished the results are saved in result. I thought if I return a value in sendRequest I get the result back. But as I mentioned before requestFinished gets the result and so sendRequest is always returning a nil variable, because at that time the request isn't finished.

What can I do to return a result? I want that this class can be used from different view controllers. So my first thought creating a method in my view controller and passing the result won't work.

I read this thread http://stackoverflow.com/questions/2878640/pass-result-of-asihttprequest-requestfinished-back-to-originating-method about using the view controller as delegate. But then I think I have to implement requestFinished and requestFailed in the view controller. The idea of not having duplicate code in different view controllers would be gone away ...

Can someone help?

Answer 1

Post an observer notification whenever you get the result and have your viewcontrollers add themselves as listeners to this notification (receiving it via [notification object]).

Answer 2

So finally I did it with a delegate.

In my abstraction class (*.h) I defined the following, otherwise you get

warning: no '-setDarkness: ' method found

warning: (Messages without a matching method signature will be assumed

warning: to return 'id' and accept '.. .' as arguments.)

@protocol RssParserDelegate <NSObject>  
    - (void)displayResults:(NSDictionary *)parserResults;
@end

Than I declared an instance variable and some methods in my abstraction class (*.h):

id _delegate;
// ...
- (id)delegate;  
- (void)setDelegate:(id)new_delegate;

The declaration therefore looks like (*.m):

 - (id)delegate {  
     return _delegate;  
 }  

 - (void)setDelegate:(id)new_delegate {  
     _delegate = new_delegate;  
 }

To pass the result you have to put the following code on requestFailed and requestFinished:

if ([_delegate respondsToSelector:@selector(displayResults:)])
    [_delegate displayResults:results];
else  
{   
    [NSException raise:NSInternalInconsistencyException  
                format:@"Delegate doesn't respond to displayResults:"];  
}

I redefined sendRequest and set the incoming delegate to my instance variable:

- (void)sendRequest:(NSString *)url withDelegate:(id)aDelegate {
    // set delegate to populate the results later
    [self setDelegate:aDelegate]; 

In your view controller declare this method:

- (void)displayResults:(NSDictionary *)results {
     // do some data processing
     ...
     // show data
     [self.tableView reloadData];
}

And I also changed the method call to sendRequest of my abstraction class:

[yourRequest sendRequest:@"xxx" withDelegate:self];