防止Android WebView在Xamarin环境中重新加载页面

Question

我意识到有很多与此相关的问题,但我已经尝试了所有本地开发的解决方案,并且无法让它们在Xamarin下工作.

我有一个webview,其中加载了一个URL,其中包含用于绘图的图形UI.当设备旋转时,webview会重新加载页面,并且用户的工作将丢失.

以下博客文章为此提供了最佳解决方案,并解释了广泛记录的解决方案由于以下原因而不足够:

http://www.devahead.com/blog/2012/01/preserving-the-state-of-an-android-webview-on-screen-orientation-change/

这个实现的主要问题是,无论何时旋转屏幕,都会再次创建> WebView,因为活动被销毁并且其saveState方法不会>保存完整状态,但只有一部分类似于URL的URL已加载的页面和>浏览历史记录.因此,例如,在屏幕方向改变之后,不会>保留缩放和滚动位置,有时会从网络重新加载页面.

所以我已经实现了他们的解决方案,将它从Java移植到Xamarin C#.它看起来很有希望,但每当我的活动重新加载并调用InitUi时,web_view类变量始终为null,而该示例依赖于此类变量在设备轮换之间保持其值.

任何人都知道为什么web_view失去了它的价值？

这是我的代码,它与文章完全相同,但移植到Xamarin C#.

public class EbookViewerActivity : ActionBarActivity
{
    protected WebView web_view;
    protected FrameLayout webViewPlaceholder;

    Button loadButton;
    Button downloadButton;
    EditText testUrlText;
    private string viewerPath;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        #region Set up activity and action bar

        //Create the activity screen and initialise the action bar
        base.OnCreate(savedInstanceState);
        RequestWindowFeature(WindowFeatures.NoTitle);
        SetContentView(Resource.Layout.Viewer);
        InitializeActionBar();

        //Set action bar button delegates
        ActionBar
            .AddLeftAction(new DelegateAction(Finish, Resource.Drawable.CloseIcon))
            .SetTitle("Ebook Annotator");

        //Set action bar logo
        ActionBar.SetHomeLogo(Resource.Drawable.AcmeTrainingLogo);
        #endregion

        InitUi();
    }

    private void InitUi()
    {
        Logger logger = Logger.Instance;
        // Retrieve UI elements
        webViewPlaceholder = FindViewById<FrameLayout>(Resource.Id.webViewPlaceholder);
        // Initialize the WebView if necessary
        if (web_view == null)
        {
            web_view = new WebView(this);
            web_view.Id = Resource.Id.ebookDynamicWebView;

            //web_view = FindViewById<WebView>(Resource.Id.ebookWebview);
            web_view.Settings.JavaScriptEnabled = true;
            web_view.AddJavascriptInterface(new AnnotationApiProxy(this), "AnnotationApi");
            string ebookId = Intent.GetStringExtra("ebookId");
            string userEmail = Intent.GetStringExtra("userEmail");
            Ebook ebook = EbookManager.GetEbook(int.Parse(ebookId));

            GlobalVariableHolder.Instance.EbookToOpen = int.Parse(ebookId);
            viewerPath = "file:///android_asset/Annotator/annotator.html";

            web_view.Settings.AllowFileAccess = true;
            logger.WriteToLog("Loading test harness with ebook id: " + ebookId, LogEntryLevel.Message);
            web_view.SetWebChromeClient(new EbookWebViewClient() { });
           // web_view.SetWebViewClient(new WebViewClient());
            AnnotationDownloader annotationDownloader = new AnnotationDownloader();
           // annotationDownloader.XmlDownloaded += (sender, args) => RunOnUiThread(() =>
         //   {
                web_view.LoadUrl(viewerPath);
           // });
            annotationDownloader.GetLatestEWorkBookXml(ebook.ID, userEmail);
        }

        // Attach the WebView to its placeholder
        webViewPlaceholder.AddView(web_view);
    }

    protected override void OnSaveInstanceState(Bundle outState)
    {
        base.OnSaveInstanceState(outState);
        // Save the state of the WebView
        web_view.SaveState(outState);
    }

    protected override void OnRestoreInstanceState(Bundle savedInstanceState)
    {
        base.OnRestoreInstanceState(savedInstanceState);
        // Restore the state of the WebView
        web_view.RestoreState(savedInstanceState);
    }

    public override void OnConfigurationChanged(Configuration newConfig)
    {
        if (web_view != null)
        {
            // Remove the WebView from the old placeholder
            webViewPlaceholder.RemoveView(web_view);
        }
        base.OnConfigurationChanged(newConfig);
        // Load the layout resource for the new configuration
        SetContentView(Resource.Layout.Viewer);
        // Reinitialize the UI
        InitUi();
    }
}

Answer 1

不要更改 AndroidManifest.xml并使用自定义属性。

[Activity(ConfigurationChanges=ConfigChanges.Orientation | ConfigChanges.ScreenSize)] 
    public partial class MyActivity : Activity { ...

这个解决方案对我有用。