Invoke API

Sencha Space is a new way to manage, deploy, and secure HTML5 applications on mobile devices. Invoke is a JavaScript API that lets one application securely run and communicate with another application. You can add the Invoke API to applications that you deploy in Sencha Space. Invoke represents a new way of building HTML5 applications. Your applications no longer have to be like islands connected only by a round trip to a server. Using Invoke, applications communicate directly, which lets you build simpler, single purpose applications that expose a simple API.

You can see Invoke in action at: http://vimeo.com/73736732

The video shows:

  1. An application invoking the Photo app
  2. Successful invocation of the Photo app from the first app
  3. Selecting photos using the externally invoked Photo app
  4. Returning the selected photos to the app that first initiated the invoke call

Using Invoke in the Foreground and Background

Applications can communicate using Invoke:

  • Foreground - Invoke calls enable a user to switch from one application to another. The user can then do work in the second application and when done, Sencha Space returns the user to the application they started from. A simple example of this is photos. In Sencha Space, you can have an application that knows where all of your organization’s photos are. When another application needs a photo, it redirects the user to the Photos application. The user can select the photos they want, and then the user is returned to the application they started with, and the application has the list of photos the user selected.

  • Background - Invoke calls open up the possibility of a new class of application communication. Applications can exchange data in the background asynchronously without the user needing to leave the application they are currently in. For example, a Contacts application can communicate with a chat application to get the online/offline status of the current contact and update the contact record. The Contacts application need not integrate a chat library or maintain a connection with a chat/presence server. The application only needs to make a simple API call to the chat application running in Sencha Space.

Include the Sencha Space APIs

You can add the Invoke API by including one statement in your HTML5 or web site application. The application need not have been created using a Sencha product.

<script src="http://space.sencha.io/space.js"></script>

Invoke Applications in the Foreground

To communicate with another application, get a connection to it:

Ext.space.Invoke.get('photos').then(send, failure);

If the application doesn’t exist or your application doesn’t have permission to call that application, Sencha Space calls your app’s failure callback:

var failure = function(error) {
    console.log('Could not find photos app', error);
}

When you have a connection, your application can start sending messages, in this case, requesting all the photos taken in the current day (time: 1d):

var send = function(connection) {
    connection.send({tags: ['keynote', 'space'], time: '1d'}, true).then(usePhoto, failure);
};

The first parameter of send is the JSON data you want to send to the application. The second parameter is the foreground and background Boolean. A value of true indicates foreground and false is background.

The user is taken to the Photos application, allowed to select photos, and then the Photos application returns the list of photos to your application using a callback:

var usePhoto = function(photos) {
    log('user selected photos', photos);
}

See the full source code for the Photos application.

Invoke Application in the Background

In the next example, an app calls the chat application in the background to get the presence of a user. The API calls are nearly identical to the previous example, except that second parameter of the send function is set to false to indicate that the application runs in the background.

Ext.space.Invoke.get('chat').then(send, failure);

var send = function(connection) {
        connection.send(
            {type: 'presence', 
                 user: 'joe.schmo@sencha.com'}, false)
            .then(
        success,
        failure
    );
};
var success = function(message) {
    console.log(message);
};

//output

{user: "polly.pocket@sencha.com", connected: true, status: 'away' }

Handling Incoming Messages From Another Application

Handling messages from other applications is accomplished with the onMessage API. The onMessage function receives the JSON message, and creates and returns an Ext.Promise request. The Promise must be resolved to return data to the calling application.

Ext.space.Invoke.onMessage(function(senderId, message) {
    var promise = new Ext.Promise(); 
    handleMessage(message, promise); 
    return promise; 
});

In handleMessage, the user info is fetched asynchronously and the response returns to fulfill the promise, else a rejection message is sent back to the calling application indicating an error.

function handleMessage(message, promise) {
    if(message.type == "presence") {
        this.getUser(message.user, function(user){
            var response = {user: user.email, 
                            connected: user.isConnected, 
                            status: user.status};
            promise.fulfill(response);
        })
    } else {
         promise.reject('Message is not understood');
    }
}
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