Quickview
-
Use
WebView
to display web pages in your Android application layout - You can create interfaces from your JavaScript to your client-side Android code
In this document
Key classes
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
WebView
. The
WebView
class is an
extension of Android's
View
class that allows you to display web pages as a
part of your activity layout. It does
not
include any features of a fully developed web
browser, such as navigation controls or an address bar. All that
WebView
does, by default, is show a web page.
A common scenario in which using
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
Activity
that contains a
WebView
, then use that to display your document that's
hosted online.
Another scenario in which
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
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
WebView
in your Android application that loads the web
page.
This document shows you how to get started with
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.
Adding a WebView to Your Application
To add a
WebView
to your Application, simply include the
<WebView>
element in your activity layout. For example, here's a layout file in which the
WebView
fills the screen:
<?xml version="1.0" encoding="utf-8"?> <WebView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/webview" android:layout_width="fill_parent" android:layout_height="fill_parent" />
To load a web page in the
WebView
, use
loadUrl()
. For example:
WebView myWebView = (WebView) findViewById(R.id.webview); myWebView.loadUrl("http://www.example.com");
Before this will work, however, your application must have access to the Internet. To get
Internet access, request the
INTERNET
permission in your
manifest file. For example:
<manifest ... > <uses-permission android:name="android.permission.INTERNET" /> ... </manifest>
That's all you need for a basic
WebView
that displays a web page.
Using JavaScript in WebView
If the web page you plan to load in your
WebView
use JavaScript, you
must enable JavaScript for your
WebView
. Once JavaScript is enabled, you can
also create interfaces between your application code and your JavaScript code.
Enabling JavaScript
JavaScript is disabled in a
WebView
by default. You can enable it
through the
WebSettings
attached to your
WebView
. You can retrieve
WebSettings
with
getSettings()
, then enable
JavaScript with
setJavaScriptEnabled()
.
For example:
WebView myWebView = (WebView) findViewById(R.id.webview); WebSettings webSettings = myWebView.getSettings(); webSettings.setJavaScriptEnabled(true);
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
WebView
in your Android application,
then you can define a
custom user agent string with
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.
Binding JavaScript code to Android code
When developing a web application that's designed specifically for the
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
Dialog
, instead of using JavaScript's
alert()
function.
To bind a new interface between your JavaScript and Android code, call
addJavascriptInterface()
, passing it
a class instance to bind to your JavaScript and an interface name that your JavaScript can call to
access the class.
For example, you can include the following class in your Android application:
public class WebAppInterface { Context mContext; /** Instantiate the interface and set the context */ WebAppInterface(Context c) { mContext = c; } /** Show a toast from the web page */ @JavascriptInterface public void showToast(String toast) { Toast.makeText(mContext, toast, Toast.LENGTH_SHORT).show(); } }
Caution:
If you've set your
targetSdkVersion
to 17 or higher,
you
must add the
@JavascriptInterface
annotation
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.
In this example, the
WebAppInterface
class allows the web page to create a
Toast
message, using the
showToast()
method.
You can bind this class to the JavaScript that runs in your
WebView
with
addJavascriptInterface()
and
name the interface
Android
. For example:
WebView webView = (WebView) findViewById(R.id.webview); webView.addJavascriptInterface(new WebAppInterface(this), "Android");
This creates an interface called
Android
for JavaScript running in the
WebView
. At this point, your web application has access to the
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:
<input type="button" value="Say hello" onClick="showAndroidToast('Hello Android!')" /> <script type="text/javascript"> function showAndroidToast(toast) { Android.showToast(toast); } </script>
There's no need to initialize the
Android
interface from JavaScript. The
WebView
automatically makes it
available to your web page. So, at the click of the button, the
showAndroidToast()
function uses the
Android
interface to call the
WebAppInterface.showToast()
method.
Note: The object that is bound to your JavaScript runs in another thread and not in the thread in which it was constructed.
Caution:
Using
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
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
addJavascriptInterface()
unless
you wrote all of the HTML and JavaScript that appears in your
WebView
. You
should also not allow the user to
navigate to other web pages that are not your own, within your
WebView
(instead, allow the user's
default browser application to open foreign links—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).
Handling Page Navigation
When the user clicks a link from a web page in your
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
WebView
,
so links open within your
WebView
. You can then allow the user to navigate
backward and forward through their web page history that's maintained by your
WebView
.
To open links clicked by the user, simply provide a
WebViewClient
for your
WebView
, using
setWebViewClient()
. For example:
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.
setWebViewClient
(new WebViewClient());
That's it. Now all links the user clicks load in your
WebView
.
If you want more control over where a clicked link load, create your own
WebViewClient
that overrides the
shouldOverrideUrlLoading()
method. For example:
private class MyWebViewClient extends WebViewClient {
@Override
public boolean
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;
}
}
Then create an instance of this new
WebViewClient
for the
WebView
:
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.
setWebViewClient
(new MyWebViewClient());
Now when the user clicks a link, the system calls
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
not
override the URL
loading (it allows the
WebView
to load the URL as usual). If the URL host
does not match, then an
Intent
is created to
launch the default Activity for handling URLs (which resolves to the user's default web
browser).
Navigating web page history
When your
WebView
overrides URL loading, it automatically accumulates a
history of visited web
pages. You can navigate backward and forward through the history with
goBack()
and
goForward()
.
For example, here's how your
Activity
can use the device
Back
button
to navigate backward:
@Override public booleanonKeyDown
(int keyCode, KeyEvent event) { // Check if the key event was the Back button and if there's history if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebView.canGoBack
()) { myWebView.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); }
The
canGoBack()
method returns
true if there is actually web page history for the user to visit. Likewise, you can use
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,
goBack()
or
goForward()
does nothing.