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Xamarin.Android Web View

  • Artikkeli

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 Activity that can view and navigate web pages.

Create a new project named HelloWebView.

Open Resources/Layout/Main.axml and insert the following:

<?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" />

Because this application will access the Internet, you must add the appropriate permissions to the Android manifest file. Open your project's properties to specify which permissions your application requires to operate. Enable the INTERNET permission as shown below:

Setting the INTERNET permission in the Android Manifest

Now open MainActivity.cs and add a using directive for Webkit:

using Android.Webkit;

At the top of the MainActivity class, declare a WebView object:

WebView web_view;

When the WebView is asked to load a URL, it will by default delegate the request to the default browser. To have the WebView load the URL (rather than the default browser), you must subclass Android.Webkit.WebViewClient and override the ShouldOverriderUrlLoading method. An instance of this custom WebViewClient is provided to the WebView. To do this, add the following nested HelloWebViewClient class inside MainActivity:

public class HelloWebViewClient : WebViewClient
{
    public override bool ShouldOverrideUrlLoading (WebView view, string url)
    {
        view.LoadUrl(url);
        return false;
    }
}

When ShouldOverrideUrlLoading returns false, it signals to Android that the current WebView instance handled the request and that no further action is necessary.

If you are targeting API level 24 or later, use the overload of ShouldOverrideUrlLoading that takes an IWebResourceRequest for the second argument instead of a string:

public class HelloWebViewClient : WebViewClient
{
    // For API level 24 and later
    public override bool ShouldOverrideUrlLoading (WebView view, IWebResourceRequest request)
    {
        view.LoadUrl(request.Url.ToString());
        return false;
    }
}

Next, use the following code for the OnCreate()) method:

protected override void OnCreate (Bundle bundle)
{
    base.OnCreate (bundle);

    // Set our view from the "main" layout resource
    SetContentView (Resource.Layout.Main);

    web_view = FindViewById<WebView> (Resource.Id.webview);
    web_view.Settings.JavaScriptEnabled = true;
    web_view.SetWebViewClient(new HelloWebViewClient());
    web_view.LoadUrl ("https://www.xamarin.com/university");
}

This initializes the member WebView with the one from the Activity layout and enables JavaScript for the WebView with JavaScriptEnabled = true (see the Call C# from JavaScript recipe for information about how to call C# functions from JavaScript). Finally, an initial web page is loaded with LoadUrl(String).

Build and run the app. You should see a simple web page viewer app as the one seen in the following screenshot:

Example of app displaying a WebView

To handle the BACK button key press, add the following using statement:

using Android.Views;

Next, add the following method inside the HelloWebView Activity:

public override bool OnKeyDown (Android.Views.Keycode keyCode, Android.Views.KeyEvent e)
{
    if (keyCode == Keycode.Back && web_view.CanGoBack ())
    {
        web_view.GoBack ();
        return true;
    }
    return base.OnKeyDown (keyCode, e);
}

This OnKeyDown(int, KeyEvent) callback method will be called whenever a button is pressed while the Activity is running. The condition inside uses the KeyEvent to check whether the key pressed is the BACK button and whether the WebView is actually capable of navigating back (if it has a history). If both are true, then the GoBack() method is called, which will navigate back one step in the WebView history. Returning true indicates that the event has been handled. If this condition is not met, then the event is sent back to the system.

Run the application again. You should now be able to follow links and navigate back through the page history:

Example screenshots of the Back button in action

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.