guide/webapps/webview.jd

page.title=Building Web Apps in WebView
@jd:body

<div id="qv-wrapper">
<div id="qv">
<h2>Quickview</h2>
<ul>
  <li>Use {@link android.webkit.WebView} to display web pages in your Android application
layout</li>
  <li>You can create interfaces from your JavaScript to your client-side Android code</li>
</ul>

<h2>In this document</h2>
<ol>
  <li><a href="#AddingWebView">Adding a WebView to Your Application</a></li>
  <li><a href="#UsingJavaScript">Using JavaScript in WebView</a>
    <ol>
      <li><a href="#EnablingJavaScript">Enabling JavaScript</a></li>
      <li><a href="#BindingJavaScript">Binding JavaScript code to Android code</a></li>
    </ol>
  </li>
  <li><a href="#HandlingNavigation">Handling Page Navigation</a>
    <ol>
      <li><a href="#NavigatingHistory">Navigating web page history</a></li>
    </ol>
  </li>
</ol>

<h2>Key classes</h2>
<ol>
  <li>{@link android.webkit.WebView}</li>
  <li>{@link android.webkit.WebSettings}</li>
  <li>{@link android.webkit.WebViewClient}</li>
</ol>

</div>
</div>

<p>If you want to deliver a web application (or just a web page) as a part of a client application,
you can do it using {@link android.webkit.WebView}. The {@link android.webkit.WebView} class is an
extension of Android's {@link android.view.View} class that allows you to display web pages as a
part of your activity layout. It does <em>not</em> include any features of a fully developed web
browser, such as navigation controls or an address bar. All that {@link android.webkit.WebView}
does, by default, is show a web page.</p>

<p>A common scenario in which using {@link android.webkit.WebView} is helpful is when you want to
provide information in your application that you might need to update, such as an end-user agreement
or a user guide. Within your Android application, you can create an {@link android.app.Activity}
that contains a {@link android.webkit.WebView}, then use that to display your document that's
hosted online.</p>

<p>Another scenario in which {@link android.webkit.WebView} can help is if your application provides
data to the user that
always requires an Internet connection to retrieve data, such as email. In this case, you might
find that it's easier to build a {@link android.webkit.WebView} in your Android application that
shows a web page with all
the user data, rather than performing a network request, then parsing the data and rendering it in
an Android layout. Instead, you can design a web page that's tailored for Android devices
and then implement a {@link android.webkit.WebView} in your Android application that loads the web
page.</p>

<p>This document shows you how to get started with {@link android.webkit.WebView} and how to do some
additional things, such as handle page navigation and bind JavaScript from your web page to
client-side code in your Android application.</p>


<h2 id="AddingWebView">Adding a WebView to Your Application</h2>

<p>To add a {@link android.webkit.WebView} to your Application, simply include the {@code
<WebView>} element in your activity layout. For example, here's a layout file in which the
{@link android.webkit.WebView} fills the screen:</p>

<pre>
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&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"
/&gt;
</pre>

<p>To load a web page in the {@link android.webkit.WebView}, use {@link
android.webkit.WebView#loadUrl(String) loadUrl()}. For example:</p>

<pre>
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.loadUrl("http://www.example.com");
</pre>

<p>Before this will work, however, your application must have access to the Internet. To get
Internet access, request the {@link android.Manifest.permission#INTERNET} permission in your
manifest file. For example:</p>

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

<p>That's all you need for a basic {@link android.webkit.WebView} that displays a web page.</p>


<h2 id="UsingJavaScript">Using JavaScript in WebView</h2>

<p>If the web page you plan to load in your {@link android.webkit.WebView} use JavaScript, you
must enable JavaScript for your {@link android.webkit.WebView}. Once JavaScript is enabled, you can
also create interfaces between your application code and your JavaScript code.</p>


<h3 id="EnablingJavaScript">Enabling JavaScript</h3>

<p>JavaScript is disabled in a {@link android.webkit.WebView} by default. You can enable it
through the {@link
android.webkit.WebSettings} attached to your {@link android.webkit.WebView}. You can retrieve {@link
android.webkit.WebSettings} with {@link android.webkit.WebView#getSettings()}, then enable
JavaScript with {@link android.webkit.WebSettings#setJavaScriptEnabled(boolean)
setJavaScriptEnabled()}.</p>

<p>For example:</p>

<pre>
WebView myWebView = (WebView) findViewById(R.id.webview);
WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
</pre>

<p>{@link android.webkit.WebSettings} provides access to a variety of other settings that you might
find useful. For example, if you're developing a web application
that's designed specifically for the {@link android.webkit.WebView} in your Android application,
then you can define a
custom user agent string with {@link android.webkit.WebSettings#setUserAgentString(String)
setUserAgentString()}, then query the custom user agent in your web page to verify that the
client requesting your web page is actually your Android application.</p>

<h3 id="BindingJavaScript">Binding JavaScript code to Android code</h3>

<p>When developing a web application that's designed specifically for the {@link
android.webkit.WebView} in your Android
application, you can create interfaces between your JavaScript code and client-side Android code.
For example, your JavaScript code can call a method in your Android code to display a {@link
android.app.Dialog}, instead of using JavaScript's {@code alert()} function.</p>

<p>To bind a new interface between your JavaScript and Android code, call {@link
android.webkit.WebView#addJavascriptInterface(Object,String) addJavascriptInterface()}, passing it
a class instance to bind to your JavaScript and an interface name that your JavaScript can call to
access the class.</p>

<p>For example, you can include the following class in your Android application:</p>

<pre>
public class WebAppInterface {
    Context mContext;

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

    /** Show a toast from the web page */
    &#64;JavascriptInterface
    public void showToast(String toast) {
        Toast.makeText(mContext, toast, Toast.LENGTH_SHORT).show();
    }
}
</pre>

<p class="caution"><strong>Caution:</strong> If you've set your <a
href="{@docRoot}guide/topics/manifest/uses-sdk-element.html#target">{@code targetSdkVersion}</a>
to 17 or higher, <strong>you
must add the <code>&#64;JavascriptInterface</code> annotation</strong> to any method that you want
available to your JavaScript (the method must also be public). If you do not provide the
annotation, the method is not accessible by your web page when running on Android 4.2 or
higher.</p>

<p>In this example, the {@code WebAppInterface} class allows the web page to create a {@link
android.widget.Toast} message, using the {@code showToast()} method.</p>

<p>You can bind this class to the JavaScript that runs in your {@link android.webkit.WebView} with
{@link android.webkit.WebView#addJavascriptInterface(Object,String) addJavascriptInterface()} and
name the interface {@code Android}. For example:</p>

<pre>
WebView webView = (WebView) findViewById(R.id.webview);
webView.addJavascriptInterface(new WebAppInterface(this), "Android");
</pre>

<p>This creates an interface called {@code Android} for JavaScript running in the {@link
android.webkit.WebView}. At this point, your web application has access to the {@code
WebAppInterface} class. For example, here's some HTML and JavaScript that creates a toast
message using the new interface when the user clicks a button:</p>

<pre>
&lt;input type="button" value="Say hello" onClick="showAndroidToast('Hello Android!')" /&gt;

&lt;script type="text/javascript"&gt;
    function showAndroidToast(toast) {
        Android.showToast(toast);
    }
&lt;/script&gt;
</pre>

<p>There's no need to initialize the {@code Android} interface from JavaScript. The {@link
android.webkit.WebView} automatically makes it
available to your web page. So, at the click of the button, the {@code showAndroidToast()}
function uses the {@code Android} interface to call the {@code WebAppInterface.showToast()}
method.</p>

<p class="note"><strong>Note:</strong> The object that is bound to your JavaScript runs in
another thread and not in the thread in which it was constructed.</p>

<p class="caution"><strong>Caution:</strong> Using {@link
android.webkit.WebView#addJavascriptInterface(Object,String) addJavascriptInterface()} allows
JavaScript to control your Android application. This can be a very useful feature or a dangerous
security issue. When the HTML in the {@link android.webkit.WebView} is untrustworthy (for example,
part or all of the HTML
is provided by an unknown person or process), then an attacker can include HTML that executes
your client-side code and possibly any code of the attacker's choosing. As such, you should not use
{@link android.webkit.WebView#addJavascriptInterface(Object,String) addJavascriptInterface()} unless
you wrote all of the HTML and JavaScript that appears in your {@link android.webkit.WebView}. You
should also not allow the user to
navigate to other web pages that are not your own, within your {@link android.webkit.WebView}
(instead, allow the user's
default browser application to open foreign links&mdash;by default, the user's web browser
opens all URL links, so be careful only if you handle page navigation as described in the
following section).</p>


<h2 id="HandlingNavigation">Handling Page Navigation</h2>

<p>When the user clicks a link from a web page in your {@link android.webkit.WebView}, the default
behavior is
for Android to launch an application that handles URLs. Usually, the default web browser opens and
loads the destination URL. However, you can override this behavior for your {@link
android.webkit.WebView},
so links open within your {@link android.webkit.WebView}. You can then allow the user to navigate
backward and forward through their web page history that's maintained by your {@link
android.webkit.WebView}.</p>

<p>To open links clicked by the user, simply provide a {@link
android.webkit.WebViewClient} for your {@link android.webkit.WebView}, using {@link
android.webkit.WebView#setWebViewClient(WebViewClient) setWebViewClient()}. For example:</p>

<pre>
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.{@link android.webkit.WebView#setWebViewClient(WebViewClient) setWebViewClient}(new WebViewClient());
</pre>

<p>That's it. Now all links the user clicks load in your {@link android.webkit.WebView}.</p>

<p>If you want more control over where a clicked link load, create your own {@link
android.webkit.WebViewClient} that overrides the {@link
android.webkit.WebViewClient#shouldOverrideUrlLoading(WebView,String)
shouldOverrideUrlLoading()} method. For example:</p>

<pre>
private class MyWebViewClient extends WebViewClient {
    &#64;Override
    public boolean {@link android.webkit.WebViewClient#shouldOverrideUrlLoading(WebView,String) shouldOverrideUrlLoading}(WebView view, String url) {
        if (Uri.parse(url).getHost().equals("www.example.com")) {
            // This is my web site, so do not override; let my WebView load the page
            return false;
        }
        // Otherwise, the link is not for a page on my site, so launch another Activity that handles URLs
        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
        startActivity(intent);
        return true;
    }
}
</pre>

<p>Then create an instance of this new {@link android.webkit.WebViewClient} for the {@link
android.webkit.WebView}:</p>

<pre>
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.{@link android.webkit.WebView#setWebViewClient(WebViewClient) setWebViewClient}(new MyWebViewClient());
</pre>

<p>Now when the user clicks a link, the system calls
{@link android.webkit.WebViewClient#shouldOverrideUrlLoading(WebView,String)
shouldOverrideUrlLoading()}, which checks whether the URL host matches a specific domain (as defined
above). If it does match, then the method returns false in order to <em>not</em> override the URL
loading (it allows the {@link android.webkit.WebView} to load the URL as usual). If the URL host
does not match, then an {@link android.content.Intent} is created to
launch the default Activity for handling URLs (which resolves to the user's default web
browser).</p>


<h3 id="NavigatingHistory">Navigating web page history</h3>

<p>When your {@link android.webkit.WebView} overrides URL loading, it automatically accumulates a
history of visited web
pages. You can navigate backward and forward through the history with {@link
android.webkit.WebView#goBack()} and {@link android.webkit.WebView#goForward()}.</p>

<p>For example, here's how your {@link android.app.Activity} can use the device <em>Back</em> button
to navigate backward:</p>

<pre>
&#64;Override
public boolean {@link android.app.Activity#onKeyDown(int,KeyEvent) onKeyDown}(int keyCode, KeyEvent event) {
    // Check if the key event was the Back button and if there's history
    if ((keyCode == KeyEvent.KEYCODE_BACK) &amp;&amp; myWebView.{@link android.webkit.WebView#canGoBack() canGoBack}()) {
        myWebView.{@link android.webkit.WebView#goBack() goBack}();
        return true;
    }
    // If it wasn't the Back key or there's no web page history, bubble up to the default
    // system behavior (probably exit the activity)
    return super.onKeyDown(keyCode, event);
}
</pre>

<p>The {@link android.webkit.WebView#canGoBack()} method returns
true if there is actually web page history for the user to visit. Likewise, you can use {@link
android.webkit.WebView#canGoForward()} to check whether there is a forward history. If you don't
perform this check, then once the user reaches the end of the history, {@link
android.webkit.WebView#goBack()} or {@link android.webkit.WebView#goForward()} does nothing.</p>