ios - 如何从iOS内部返回方法对象

Question

方法的返回类型是NSArray，所以当我调用此方法时，将得到nil或空数组。在我的方法实现下面:

- (NSArray *)startParsing {
    __block NSArray *array;
    allProductsID = [[NSMutableArray alloc] init];
    NSString *string = [NSString stringWithFormat:@"http://%@:@%@",kPrestaShopAPIKey, kPrestaShopURLString];
    NSURL *url = [NSURL URLWithString:string];

    AFHTTPRequestOperationManager *manager = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:url];
    manager.responseSerializer = [AFXMLParserResponseSerializer serializer];

    [manager GET:@"categories/21" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSXMLParser *parser = (NSXMLParser *)responseObject;
        [parser setShouldProcessNamespaces:YES];
        parser.delegate = self;
        [parser parse];
        //NSLog(@"First response %@", responseObject);
        for (int i = 0; i< [[self.xmlShop objectForKey:@"product"] count]; i++) {
            //NSLog(@"Second ID --> %@", [self.xmlShop objectForKey:@"product"][i]);
            NSString *productID = [NSString stringWithFormat:@"products/%@", [[self.xmlShop objectForKey:@"product"][i] objectForKey:@"id"]];
            [allProductsID addObject:productID];
        }
        array = [allProductsID copy];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Error occured %@", [error localizedDescription]);
    }];
    return array;
}

谁能帮助我解决这个问题？

Answer 1

正如昆汀已经提到的那样，您不能直接这样做，因为您是在内部执行异步请求。这意味着您的程序将启动请求，然后继续其下一条语句，而不等待请求完成。您应该做的就是

使请求同步，以使程序等待直到请求完成。但是请注意不要从主线程调用此方法，因为这将阻止您的应用继续响应，直到请求返回为止。 或

使用一个块作为startParsing方法的回调(与将块用于实际请求回调的方式相同)

例如，这会像下面这样:

- (void)startParsing:(void (^)(NSArray*))parsingFinished {
    allProductsID = [[NSMutableArray alloc] init];
    NSString *string = [NSString stringWithFormat:@"http://%@:@%@",kPrestaShopAPIKey, kPrestaShopURLString];
    NSURL *url = [NSURL URLWithString:string];

    AFHTTPRequestOperationManager *manager = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:url];
    manager.responseSerializer = [AFXMLParserResponseSerializer serializer];

    [manager GET:@"categories/21" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        // do your parsing...
        parsingFinished([allProductsID copy]);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        parsingFinished([[NSArray alloc] init]); 
        // or return nil or provide a parsingFailed callback
    }];
}

然后您会称其为

[yourObject startParsing:^(NSArray *parsedData) {
    // do something with the parsed data
}];