Developing a Plugin on BlackBerry

How to make the Echo plugin on Blackberry

This guide explores how to develop the Echo plugin on BlackBerry. If you haven't read the top-level guide about the JavaScript part of the plugin, it would be best if you read that first and then this guide. In addition, please download the Cordova Blackberry repo.

The Cordova-BlackBerry project allows you to deploy to BlackBerry devices such a the Torch and Bold, as well as the Playbook. There's a difference between deploying to normal BlackBerry handheld devices and the Playbook. They use two different code bases, so when you develop for one, you have to duplicate your efforts for the other! This guide focuses on the handheld devices rather than the tablet. (In the future, this guide should cover both platforms.)

Continuing on from the previous guide, the Echo plugin essentially returns whatever message a user provides to the window.echo function.

The Echo function:

window.echo = function(str, callback) {
        cordova.exec(callback, function(err) {
            callback('Nothing to echo.');
        }, "Echo", "echo", [str]);
    };

Modifying plugins.xml

Your project's www/plugins.xml folder contains all of the necessary references to your Cordova project's plugins. Add an additional reference so that when cordova.exec is called, Cordova knows how to map the Echo argument of cordova.exec to the Echo class that we want to write natively:

<plugins>
  ...
  <plugin name="Echo" value="org.apache.cordova.echo.Echo"/>
  ...
</plugins>

Adding Echo.java

If you notice the structure of the value attribute, you'll see a defined path that leads to the Echo plugin. In the root folder of the Cordova BlackBerry WebWorks repo, look for a folder called framework. This folder contains all of the source code that runs natively on the BlackBerry. Navigate to framework/ext/src/org/apache/cordova. At this point, you'll see all of the plugin folders, inside of which is the source code. So add the folder echo to framework/ext/src/org/apache/cordova/echo and create a file called Echo.java at framework/ext/src/org/apache/cordova/echo/Echo.java.

Writing Echo.java

The basic idea behind writing a plugin is to create a class that extends the Plugin class and have a method called execute to return a PluginResult class. Any call to cordova.exec passes in the action to execute within the class, as well as the arguments. In this case, "echo" is the action we want to execute within the class "Echo" and [str] are the arguments we are passing in.

package org.apache.cordova.echo;

import org.apache.cordova.api.Plugin;
import org.apache.cordova.api.PluginResult;
import org.apache.cordova.json4j.JSONArray;
import org.apache.cordova.json4j.JSONException;
import org.apache.cordova.json4j.JSONObject;
/**
 * A simple plugin to demonstrate how to build a plugin for Blackberry
 * Basically echos back the msg that a user calls to this plugin
 */
public final class Echo extends Plugin {

    public static final String echo = "echo";

    public PluginResult execute(String action, JSONArray args, String callbackId) {
        PluginResult result = new PluginResult(PluginResult.Status.INVALID_ACTION, "Echo: Invalid action:" + action);
        if(action.equals(echo)){
            try {
                String theMsg = args.getString(0);
                if(theMsg!= null || theMsg.length()>0){
                    result = new PluginResult(PluginResult.Status.OK, theMsg);
                }else{
                    result = new PluginResult(PluginResult.Status.ERROR, "Nothing to echo.");
                }
            } catch (JSONException e) {
                result = new PluginResult(PluginResult.Status.JSON_EXCEPTION, e.getMessage());
            }
        }

        return result;
    }

}

So if we look at the code above, we can see that within the execute method, we are first looking for what actions are coming in. The Echo plugin has only one action, echo, so we will be only checking for that. If our plugin had more actions, it's simply a matter of adding more conditional tests to check for those actions.

We are then going to grab the message coming in from the arguments which is supplied by the args parameter. We can grab the first argument by simply doing String theMsg = args.getString(0);.

We will do some error checking and if the message looks okay, we will instantiate a new PluginResult with an ok status: PluginResult.Status.OK and return the message: theMsg. After this, we return the result which to be passed back to JavaScript to be fired in the success callback. If something fails, we can return various status exceptions like PluginResult.Status.ERROR, PluginResult.Status.JSON_EXCEPTION, or PluginResult.Status.INVALID_ACTION. When passed back, these types of results fire the fail callback in JavaScript.

Updating the .jar in your project's www folder

The added Echo.java needs to be updated in your project. To build the .jar file, Navigate to the BlackBerry WebWorks repo's root directory and run the ant command:

ant update -Dproject.path="~/path_to_my_project"

This builds a new .jar file in the build/ext directory. Copy the build/ext/cordova.jar file into your project/www/ext directory.

If all goes well, that allows you to use the Echo plugin in BlackBerry.