Android - Using native features, through Javascript

This follows on from the previous post.

JavaScriptInterface

At this stage, we have a working app that can load a webpage, with Javascript enabled. The next step is to allow us to use the native features on the device, through the webview. Examples of this include:

  • Geolocation
  • Device information, such as battery levels, network status.
  • Controlling hardware, such as the camera and vibration.
  • Native sharing, using the apps installed on the device.
  • Anything else that the device is capable of.

A new class needs to be created in the MainActivity.java file, after the onCreate() method, like so:

public class jsBridge {
    Context mContext;

    /** Instantiate the interface and set the context */
    jsBridge(Context c) {
        mContext = c;
    }

    /** Show a toast from the web page */
    @JavascriptInterface
    public void showMessage(String message) {
        Toast.makeText(mContext, message, Toast.LENGTH_SHORT).show();
    }
}

Note: If eclipse shows a load of errors for some of the variables, hover over the error, and select import___.

We then assign this to our webView, like so

webView.addJavascriptInterface(new jsBridge(this), "Android");

Then, on our HTML page, we can add the Javascript that would natively show a message on the device:

<script type="text/javascript">
    Android.showMessage("Hello!");
</script>

There are hundreds more features that can be added to the JavaScriptInterface, for example, controlling the camera, recording audio, making the device vibrate, enabling WiFi, using the compass or getting information like the battery level.

For more examples of specific features, leave a comment.


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