Invoking Services Asynchronously from Your iOS App

The main drawback of using synchronous requests from your app is that each request must terminate before another can begin. If you’re sending a large number of synchronous requests, performance suffers as a bottleneck forms while each one waits to be processed. Fortunately, Liferay’s iOS SDK allows asynchronous HTTP requests. To do so, you need to set a callback to the session object. If you want to make synchronous requests again, you can set the callback to nil.

With the following steps, this tutorial shows you how to implement asynchronous requests in your iOS app:

  1. Implement your callback class.
  2. Instantiate your callback class and set it to the session.
  3. Call Liferay services.

Objective-C is used in the code snippets that follow. Let the requesting begin!

Implementing Your Callback Class

To configure asynchronous requests, first create a class that conforms to the LRCallback protocol. When implementing this callback class, you need to implement its onFailure and onSuccess methods. These methods respectivley determine what your app does when the request fails or succeeds. If a server side exception or a connection error occurs during the request, the onFailure method is called with an NSError instance that contains information about the error. Note that the onSuccess result parameter doesn’t have a specific type. When deciding what to cast it to, you need to check the type in the service method signature.

The example code here implements a callback class for an app that retrieves blog entries from a Blogs portlet. The service method for this call is getGroupEntriesWithGroupId, which returns an NSArray instance. The onSuccess method’s result parameter is therefore cast to this type:

#import "LRCallback.h"

@interface BlogsEntriesCallback : NSObject <LRCallback>


#import "BlogsEntriesCallback.h"

@implementation BlogsEntriesCallback

- (void)onFailure:(NSError *)error {
    // Implement error handling code

- (void)onSuccess:(id)result {
    // Called after request has finished successfully
    NSArray *entries = (NSArray *)result;


Awesome! Now you have a callback class that you can use with the session.

Set the Callback to the Session

Next, create an instance of this callback and set it to the session. If you haven’t created a session yet, do so now. The tutorial Invoking Liferay Services in Your iOS App shows you how to create a session. Now you’re ready to set the callback to the session. For example, this is done here for BlogsEntriesCallback:

BlogsEntriesCallback *callback = [[BlogsEntriesCallback alloc] init];

[session setCallback:callback];

Pretty simple! Now you’re ready to make the service call.

Making the Service Call

Last but certainly not least, make the service call. This is done the same as calling any other service: create a service object from the session and use it to make the service call. This is also described in the tutorial Invoking Liferay Services in Your iOS App. Here, an example service call that gets all the blog entries from a site’s Blogs portlet is shown:

[service getGroupEntriesWithGroupId:10184 status:0 start:-1 end:-1 error:&error];

Since the request is asynchronous, getGroupEntriesWithGroupId immediately returns nil. Once the request finishes successfully, the onSuccess method of your callback is invoked with the results on the main UI thread.

Great! Now you know how to make asynchronous requests in your iOS apps. However, there’s another way to accomplish the same thing. This is discussed next.

Using Blocks as Callbacks

Instead of implementing a separate callback class, you can use an Objective-C block as a callback. An example of this is shown here for an asynchronous call that retrieves a user’s sites. Note that this includes all the code required to make the call:

LRSession *session = [[LRSession alloc] 
    initWithServer:@"http://localhost:8080" username:@"[email protected]" password:@"test"];

    onSuccess:^(id result) {
        // Called after request has finished successfully
    onFailure:^(NSError *e) {
        // Implement error handling code

LRGroupService_v62 *service = [[LRGroupService_v62 alloc] initWithSession:session];

NSError *error;
[service getUserSites:&error];

When using a block as a callback, take care not to also set an LRCallback instance to the session. If you do, it gets overriden. Otherwise, support for blocks works the same way as described in the previous sections.

Super! Now you know two different ways to make asynchronous service requests in your iOS apps.

Related Topics

Invoking Liferay Services in Your iOS App

Creating Android Apps that Use Liferay

Service Builder and Services

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