how to load data after entering a viewController?

Question

I have a viewController that contains some GIF images,load these images cost a lot of memory ,so it takes me seconds to enter this viewController everytime,is there any way I can enter this viewCOntroller first,then load the data? I don't know NSThread will work or not.My english is poor,hope you can understand my question.Thx.

`viewDidAppear` not `viewDidLoad` – Ty Lertwichaiworawit Oct 22 '15 at 06:38 — Ty Lertwichaiworawit, Oct 22 '15 at 06:38

score 2 · Accepted Answer · answered Oct 22 '15 at 06:37

2

yes, the easiest way is to use grand central dispatch

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ //enter a background thread
  UIImage * img = [UIImage imageNamed:@"image.jpg"]; //load image in background

  dispatch_sync(dispatch_get_main_queue(), ^{ //return to main thread
      [[self imageView] setImage: img]; //set the imageViews image
  });
});

answered Oct 22 '15 at 06:37

Fonix

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It works,there is no time-delay now :) But there's something wrong with my GIFS,that's another problem,so thank you! – Jiahao Jiang Oct 22 '15 at 07:09
Where to implement this? In view did load? – Bhavin Ramani Oct 22 '15 at 09:27
@bhavinramani yep, or `viewWillAppear`, would be inefficient to do it in `viewDidAppear` though as the delay in calling that function would just needlessly delay the loading of your images – Fonix Oct 23 '15 at 01:55

Inder Kumar Rathore · Answer 2 · 2015-10-22T07:17:47.213

1

Just write your code in viewDidAppear: or use a thread in viewDidLoad

dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    // Add your image creation code here e.g.
    UIImage *image = [UIImage imageNamed:@"yourImage.png"];
    dispatch_async( dispatch_get_main_queue(), ^{
        // Add code here to update the UI
        self.imageView = image;
    });
});

edited Oct 22 '15 at 07:17

answered Oct 22 '15 at 06:37

Inder Kumar Rathore

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I use this method and change the priority to DISPATCH_QUEUE_PRIORITY_BACKGROUND,so it works well,thank you! Can I accept two different answers? – Jiahao Jiang Oct 22 '15 at 07:15
No you can't accept two answer but surely you can upvote two answers – Inder Kumar Rathore Oct 22 '15 at 07:18
I only have 4 reputations,so I can't upvote any answer :( – Jiahao Jiang Oct 22 '15 at 07:25
I guess now you have enough :) – Inder Kumar Rathore Oct 22 '15 at 07:28
I have 14 reputation now! did you give me 10 ? :):):) – Jiahao Jiang Oct 22 '15 at 07:41
sorry,acturely I have 18 now,I checked the wrong place. Now I can upvote your answers :) – Jiahao Jiang Oct 22 '15 at 07:44

score 1 · Answer 3 · answered Oct 22 '15 at 06:41

1

Do the loading of data inside the viewDidAppear method of your ViewController, so the View will appear at first without the GIFS, but as you loop getting each data, you can set the images to your view as they get loaded.

answered Oct 22 '15 at 06:41

Pietro Pepe

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2
8

score 1 · Answer 4 · answered Oct 22 '15 at 06:50

Do it like that .

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ 

 // (BackGroungThred)  here you can  retrive the image from your sources . But do not update UI in backgroung thread ..

dispatch_sync(dispatch_get_main_queue(), ^{

// (Main Thread) Update UI in main thread..

});

});

hope it help you ..

score 1 · Answer 5 · edited May 23 '17 at 11:52

There are Two options for load data after entering in a view controller

1.NSOperationQueue

NSOperationQueue *myQueue = [[NSOperationQueue alloc] init];
[myQueue addOperationWithBlock:^{
   // Background work
   UIImage * img = [UIImage imageNamed:@"image.jpg"];
  [[NSOperationQueue mainQueue] addOperationWithBlock:^{
    // Main thread work (UI usually)
    yourImageView.image = image;
}];
}];

2.Grand Central Dispatch(GCD)

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void)
{
          // Background work  
          UIImage * img = [UIImage imageNamed:@"image.jpg"];          
         dispatch_async(dispatch_get_main_queue(), ^(void)
          {
               // Main thread work (UI usually)  
               yourImageView.image = image;           

          });
});

For more details please refer the below links

thank you ,both two options are simple and easy to implement :) — Jiahao Jiang, Oct 22 '15 at 09:55
if my answer is very understandable and helpful for you,please tick my answer. — user3182143, Oct 22 '15 at 09:59

how to load data after entering a viewController?

5 Answers5