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How to Use iOS - Lazy Loading Images - Objective C


Lazy Loading Images





Objective

Main objective of this post is to give an idea about Lazy Loading Images

Introduction:

 I have implemented Lazy Loading Images in iOS app using the example provided here. Lazy Loading Images is a technique to resolve loading image from the web. The thing is that, I need to display images directly from the web in UIImageView or any other control.


You will get Final Output:

For this, if you simply try to set the image using in-built setImage method then your application gets stuck while loading image from the web. To overcome this issue, there is a technique generally known as Lazy Loading Image.

The thing actually happening in lazy loading is that the task of image loading from web is performed in background and at that time a temporary placeholder image is displayed in the control. When the actual image is fully loaded from the web, it is replaced with the placeholder image and you get your actual image on the control without having stuck interface.

Now lets look how we can implement this technique:

Step 1 Create XCode Project

First of all create an XCode project named LazyLoadingImageDemo and save it. This project will contain one ViewController. Take a UITableView control on this ViewController and set its delegate to point to this ViewController.



Step 2 Download ThirdParty from GitHub

You will need SDWebImage library, which you can download from:
SDWebImage

Download it and add this library to your application. This library contains a header file UIImageView+WebCache.h which will be used in the next step.

Step 3 Import ThirdParty File

Now go to ViewController.h file and just import the UIImageView+WebCache.h header.



Step 4 Intialised Image array

Now initialise an object of NSArray containing the URLs of the images to be displayed in viewDidLoad method as shown below:

- (void)viewDidLoad
{
      [superviewDidLoad];
      arrImagesUrl = [[NSArrayalloc] initWithObjects:
      @"http://static2.dmcdn.net/static/video/656/177/44771656:jpeg_preview_small.jpg?20120509154705",
@"http://static2.dmcdn.net/static/video/629/228/44822926:jpeg_preview_small.jpg?20120509181018",
@"http://static2.dmcdn.net/static/video/116/367/44763611:jpeg_preview_small.jpg?20120509101749",
@"http://static2.dmcdn.net/static/video/340/086/44680043:jpeg_preview_small.jpg?20120509180118",
@"http://static2.dmcdn.net/static/video/666/645/43546666:jpeg_preview_small.jpg?20120412153140",
nil];
 }

Step 5 TableView Delegate & DataSource Methods

Call the setImageWithURL:placeholderImage: method from the tableView:cellForRowAtIndexPath: UITableViewDataSource method.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     staticNSString *CellIdentifier = @"cell";

     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
     if (cell == nil)
     {
          cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefaultreuseIdentifier:CellIdentifier];
     }

     cell.textLabel.text = [NSString stringWithFormat:@"Image #%d", indexPath.row];
     cell.imageView.contentMode = UIViewContentModeScaleAspectFill;

     [cell.imageView setImageWithURL:[NSURL URLWithString:[arrImagesUrl objectAtIndex:indexPath.row]]
placeholderImage:[UIImageimageNamed:@"placeholder.png"]];
return cell;
 }
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