docs/html/resources/articles/using-webviews.jd

page.title=Using WebViews
parent.title=Articles
parent.link=../browser.html?tag=article
@jd:body

<p>A small application called <a title="WebViewDemo"
href="http://code.google.com/p/apps-for-android/source/browse/#svn/trunk/Samples
/WebViewDemo">WebViewDemo</a> shows how you can add web content to your
application. You can find it in the <a title="apps-for-android"
href="http://code.google.com/p/apps-for-android/">apps-for-android</a> project.
This application demonstrates how you can embed a {@link android.webkit.WebView}
into an activity and also how you can have two way communication between your
application and the web content. </p>

<p>A
WebView uses the same rendering and JavaScript engine as the browser,
but it runs under the control of your application. The WebView can be
full screen or you can mix it with other Views. The content for your
WebView can come from anywhere. The WebView can download content from
the web, or it can come from local files stored in your assets
directory. The content can even be dynamically generated by your
application code. For this example, the HTML comes from a local file
called <a title="demo.html" href="http://code.google.com/p/apps-for-android/source/browse/trunk/Samples/WebViewDemo/assets/demo.html">demo.html</a>.</p>

<p>This application does not do very much: when you click on the 
android, he raises his arm.</p>

<div style="text-align: center;"><img style="width: 322px; height: 482px;" src="images/webview.png"></div>

<p>This
could, of course, easily be accomplished with a little bit of
JavaScript. Instead, though, WebViewDemo takes a slightly more
complicated path to illustrate two very powerful features of WebView.</p> 

<p>First,
JavaScript running inside the WebView can call out to code in your
Activity. You can use this to have your JavaScript trigger actions like
starting a new activity, or it can be used to fetch data from a
database or {@link android.content.ContentProvider}. The API for this 
is very simple: just call the 
{@link android.webkit.WebView#addJavascriptInterface(java.lang.Object, java.lang.String) addJavascriptInterface()}
method on your WebView. You pass an object whose methods you want to
expose to JavaScript and the name to use when making calls. You can see
the exact syntax in <a title="WebViewDemo.java"
href="http://code.google.com/p/apps-for-android/source/browse/trunk/Samples/
WebViewDemo/src/com/google/android/webviewdemo/WebViewDemo.java">WebViewDemo.
java</a>. Here we are making our DemoJavascriptInterface object available to
JavaScript where it will be called "window.demo".</p>

<p>Second, your Activity can invoke JavaScript methods. All you have to do 
is call the {@link android.webkit.WebView#loadUrl(java.lang.String) loadUrl} 
method with the appropriate JavaScript call:</p>

<p><code style="padding-left: 25px;">mWebView.loadUrl("javascript:wave()");</code></p>

<p>Our <a title="WebViewDemo"
href="http://code.google.com/p/apps-for-android/source/browse/#svn/trunk/Samples
/WebViewDemo">WebViewDemo</a> uses both techniques: when you click on the
android, it calls out to the activity, which then turns around and calls back
into the JavaScript. WebViews are very powerful, and they may be a valuable tool
to help you build your application – especially if you already have a lot of
HTML content. As it happens, we've used exactly this approach in some of the
applications we've written.</p>