M7350/base/docs/html/resources/tutorials/views/hello-webview.jd

page.title=Web View
parent.title=Hello, Views
parent.link=index.html
@jd:body

<p>{@link android.webkit.WebView} allows you to create your own window for viewing web pages (or even
develop a complete browser). In this tutorial, you'll create a simple {@link android.app.Activity}
that can view and navigate web pages.</p>

<ol>
   <li>Create a new project named <em>HelloWebView</em>.</li>
   <li>Open the <code>res/layout/main.xml</code> file and insert the following:
<pre>
&lt;?xml version="1.0" encoding="utf-8"?>
&lt;WebView  xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/webview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
/>
</pre>
  </li>

   <li>Now open the <code>HelloWebView.java</code> file.
      At the top of the class, declare a {@link android.webkit.WebView} object:
<pre>WebView mWebView;</pre>
  <p>Then use the following code for the {@link android.app.Activity#onCreate(Bundle) onCreate()}
  method:</p>
<pre>
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mWebView = (WebView) findViewById(R.id.webview);
    mWebView.getSettings().setJavaScriptEnabled(true);
    mWebView.loadUrl("http://www.google.com");
}
</pre>
  <p>This initializes the member {@link android.webkit.WebView} with the one from the
  {@link android.app.Activity} layout; requests a {@link android.webkit.WebSettings} object with
  {@link android.webkit.WebView#getSettings()}; and enables JavaScript for the {@link
  android.webkit.WebView} with {@link android.webkit.WebSettings#setJavaScriptEnabled(boolean)}.
  Finally, an initial web page is loaded with {@link
  android.webkit.WebView#loadUrl(String)}.</p>
  </li>

  <li>Because this application needs access to the Internet, you need to add the appropriate
  permissions to the Android manifest file. Open the <code>AndroidManifest.xml</code> file
  and add the following as a child of the <code>&lt;manifest></code> element:

    <pre>&lt;uses-permission android:name="android.permission.INTERNET" /></pre></li>

  <li>While you're in the manifest, give some more space for web pages by removing the title
  bar, with the "NoTitleBar" theme:
<pre>
&lt;activity android:name=".HelloGoogleMaps" android:label="@string/app_name"
     <strong>android:theme="@android:style/Theme.NoTitleBar"</strong>&gt;
</pre>
  </li>

  <li>Now run the application.
  <p>You now have a simplest web page viewer.
  It's not quite a browser yet because as soon as you click a link, the default Android Browser
  handles the Intent to view a web page, because this {@link android.app.Activity} isn't
  technically enabled to do so. Instead of adding an intent filter to view web pages, you can
  override the {@link android.webkit.WebViewClient} class and enable this {@link
  android.app.Activity} to handle its own URL requests.</p>
  </li>

  <li>In the <code>HelloAndroid</code> Activity, add this nested class:
<pre>
private class HelloWebViewClient extends WebViewClient {
    &#64;Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
}
</pre>
  </li>
  <li>Then towards the end of the {@link android.app.Activity#onCreate(Bundle)} method, set an
  instance of the <code>HelloWebViewClient</code> as the {@link android.webkit.WebViewClient}:
   <pre>mWebView.setWebViewClient(new HelloWebViewClient());</pre>

    <p>This line can go anywhere following the initialization of the {@link
    android.webkit.WebView} object.</p>
    <p>This creates a {@link android.webkit.WebViewClient} that will load any URL selected from this
    {@link android.webkit.WebView} into the same {@link android.webkit.WebView}. The 
    {@link android.webkit.WebViewClient#shouldOverrideUrlLoading(WebView,String)} method is passed
the current    {@link android.webkit.WebView} and the URL requested, so all it needs to do is load
the URL in    the given view. Returning <code>true</code> says that the method has handled the URL
and the    event should not propagate (in which case, an Intent would be created that's handled by
the    Browser application).</p>
    <p>If you run the application again, new pages will now load in this Activity.
    However, you can't navigate back to previous pages. To do this, you need to handle the BACK
    button on the device, so that it will return to the previous page, rather than exit the
    application.</p>
    </li>

  <li>To handle the BACK button key press, add the following method inside the
  <code>HelloWebView</code> Activity:
<pre> 
&#64;Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK) &amp;&amp; mWebView.canGoBack()) {
        mWebView.goBack();
        return true;
    }
    return super.onKeyDown(keyCode, event);
}
</pre>
    <p>This {@link android.app.Activity#onKeyDown(int,KeyEvent)} callback method will be called
    anytime a button is pressed while in the Activity. The condition inside uses the {@link
    android.view.KeyEvent} to check whether the key pressed is the BACK button and whether the
    {@link android.webkit.WebView} is actually capable of navigating back (if it has a history). If
    both are true, then the {@link android.webkit.WebView#goBack()} method is called,
    which will navigate back one step in the {@link android.webkit.WebView}
    history.Returning <code>true</code> indicates that the event has been handled. If this condition
    is not met, then the event is sent back to the system.</p>
</li>
<li>Run the application again. You'll now be able to follow links and navigate back through the
page history.</li>
</ol>
<p>When you open the application, it should look like this:</p>
<img src="images/hello-webview.png" width="150px" />

<h3>Resource</h3>
<ul>
<li>{@link android.webkit.WebView}</li>
<li>{@link android.webkit.WebViewClient}</li>
<li>{@link android.view.KeyEvent}</li>
</ul>