Question

I am developing an iPhone app. In the app, I need to load a lot of data (JSON) from the web and then create the view accordingly. Please suggest me how to proceed.

Basically what I am doing is

1. Load a json from array a web-service.

2. The array received above contains urls to other web services. Lets say, 8

3. So now I need call 8 web services and after fetching, I have to parse the data and then show this to user.

Its the first time I am dealing with a web-service. So have no idea how to do that.

the major problem is the time consumption. How can I implement multithreading in it?

Please suggest any idea or link that could help me.

Answer 1

What i’d do:

1. Create a new NSThread and corresponding @autoreleasepool which loads the first json
2. Once the ‘main JSON’ data is loaded: Put all the url’s into a NSMutableArray
3. Load the JSON date of the first URL (again in the same thread) of the above array
4. Once the JSON data is loaded, store the JSON data
5. Remove the first element from the array you created in [2].
6. If your array isn’t empty > goto step 3.

Something like this?
(haven’t tested it):

#import "JSONKit.h"
- (void)viewDidLoad {
    [super viewDidLoad];    
    [NSThread detachNewThreadSelector:@selector(_loadJSON) toTarget:self withObject:nil];
};

-(void)_startNewThread {
    @autoreleasepool {
        NSError *error = nil;
        /*
         main json file:
         [
             { "url": "http://domain.com/file2.json" },
             { "url": "http://domain2.com/file.json" },
             { "url": "http://domain3.com/file.json" }
        ]
    */   
    NSMutableArray *mainUrls = [[NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://domain.com/file.json"] encoding:NSUTF8StringEncoding error:&error] mutableObjectFromJSONString];
    NSMutableArray *returnArray = [[NSMutableArray alloc] init];
    if (error == nil) {
        while ([mainUrls count]) {
            NSURL *url = [NSURL URLWithString:[[mainUrls objectAtIndex:0] objectForKey:@"url"]];
            NSDictionary *dictionary = [[NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&error] objectFromJSONString];
            if (error == nil) {
                [returnArray addObject:dictionary];
            }
            [mainUrls removeObjectAtIndex:0];
        }
    }
    [returnArray autorelease];
    [self performSelectorOnMainThread:@selector(_finished:) withObject:[NSArray arrayWithArray:returnArray] waitUntilDone:YES];
    }
}

-(void)_finished:(NSArray *)__array {
    NSLog(@"Result: %@", __array);
}