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[webview_flutter] Filter onChanged events for invalid displays #1964
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,142 @@ | ||
| package io.flutter.plugins.webviewflutter; | ||
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| import static android.hardware.display.DisplayManager.DisplayListener; | ||
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| import android.annotation.TargetApi; | ||
| import android.hardware.display.DisplayManager; | ||
| import android.os.Build; | ||
| import android.util.Log; | ||
| import java.lang.reflect.Field; | ||
| import java.util.ArrayList; | ||
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| /** | ||
| * Works around an Android WebView bug by filtering some DisplayListener invocations. | ||
| * | ||
| * <p>Older Android WebView versions had assumed that when {@link DisplayListener#onDisplayChanged} | ||
| * is invoked, the display ID it is provided is of a valid display. However it turns out that when a | ||
| * display is removed Android may call onDisplayChanged with the ID of the removed display, in this | ||
| * case the Android WebView code tries to fetch and use the display with this ID and crashes with an | ||
| * NPE. | ||
| * | ||
| * <p>This issue was fixed in the Android WebView code in | ||
| * https://chromium-review.googlesource.com/517913 which is available starting WebView version | ||
| * 58.0.3029.125 however older webviews in the wild still have this issue. | ||
| * | ||
| * <p>Since Flutter removes virtual displays whenever a platform view is resized the webview crash | ||
| * is more likely to happen than other apps. And users were reporting this issue see: | ||
| * https://github.com/flutter/flutter/issues/30420 | ||
| * | ||
| * <p>This class works around the webview bug by unregistering the WebView's DisplayListener, and | ||
| * instead registering its own DisplayListener which delegates the callbacks to the WebView's | ||
| * listener unless it's a onDisplayChanged for an invalid display. | ||
| * | ||
| * <p>I did not find a clean way to get a handle of the WebView's DisplayListener so I'm using | ||
| * reflection to fetch all registered listeners before and after initializing a webview. In the | ||
| * first initialization of a webview within the process the difference between the lists is the | ||
| * webview's display listener. | ||
| */ | ||
| @TargetApi(Build.VERSION_CODES.KITKAT) | ||
| class DisplayListenerProxy { | ||
| private static final String TAG = "DisplayListenerProxy"; | ||
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| private ArrayList<DisplayListener> listenersBeforeWebView; | ||
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| /** Should be called prior to the webview's initialization. */ | ||
| void onPreWebViewInitialization(DisplayManager displayManager) { | ||
| listenersBeforeWebView = yoinkDisplayListeners(displayManager); | ||
| } | ||
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| /** Should be called after the webview's initialization. */ | ||
| void onPostWebViewInitialization(final DisplayManager displayManager) { | ||
| final ArrayList<DisplayListener> webViewListeners = yoinkDisplayListeners(displayManager); | ||
| // We recorded the list of listeners prior to initializing webview, any new listeners we see | ||
| // after initializing the webview are listeners added by the webview. | ||
| webViewListeners.removeAll(listenersBeforeWebView); | ||
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| if (webViewListeners.isEmpty()) { | ||
| // The Android WebView registers a single display listener per process (even if there | ||
| // are multiple WebView instances) so this list is expected to be non-empty only the | ||
| // first time a webview is initialized. | ||
| // Note that in an add2app scenario if the application had instantiated a non Flutter | ||
| // WebView prior to instantiating the Flutter WebView we are not able to get a reference | ||
| // to the WebView's display listener and can't work around the bug. | ||
| // | ||
| // This means that webview resizes in add2app Flutter apps with a non Flutter WebView | ||
| // running on a system with a webview prior to 58.0.3029.125 may crash (the Android's | ||
| // behavior seems to be racy so it doesn't always happen). | ||
| return; | ||
| } | ||
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| for (DisplayListener webViewListener : webViewListeners) { | ||
| // Note that while DisplayManager.unregisterDisplayListener throws when given an | ||
| // unregistered listener, this isn't an issue as the WebView code never calls | ||
| // unregisterDisplayListener. | ||
| displayManager.unregisterDisplayListener(webViewListener); | ||
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| // We never explicitly unregister this listener as the webview's listener is never | ||
| // unregistered (it's released when the process is terminated). | ||
| displayManager.registerDisplayListener( | ||
| new DisplayListener() { | ||
| @Override | ||
| public void onDisplayAdded(int displayId) { | ||
| for (DisplayListener webViewListener : webViewListeners) { | ||
| webViewListener.onDisplayAdded(displayId); | ||
| } | ||
| } | ||
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| @Override | ||
| public void onDisplayRemoved(int displayId) { | ||
| for (DisplayListener webViewListener : webViewListeners) { | ||
| webViewListener.onDisplayRemoved(displayId); | ||
| } | ||
| } | ||
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| @Override | ||
| public void onDisplayChanged(int displayId) { | ||
| if (displayManager.getDisplay(displayId) == null) { | ||
| return; | ||
| } | ||
| for (DisplayListener webViewListener : webViewListeners) { | ||
| webViewListener.onDisplayChanged(displayId); | ||
| } | ||
| } | ||
| }, | ||
| null); | ||
| } | ||
| } | ||
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| @SuppressWarnings({"unchecked", "PrivateApi"}) | ||
| private static ArrayList<DisplayListener> yoinkDisplayListeners(DisplayManager displayManager) { | ||
| if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) { | ||
| // We cannot use reflection on Android O, but it shouldn't matter as it shipped | ||
| // with a WebView version that has the bug this code is working around fixed. | ||
| return new ArrayList<>(); | ||
| } | ||
| try { | ||
| Field displayManagerGlobalField = DisplayManager.class.getDeclaredField("mGlobal"); | ||
| displayManagerGlobalField.setAccessible(true); | ||
| Object displayManagerGlobal = displayManagerGlobalField.get(displayManager); | ||
| Field displayListenersField = | ||
| displayManagerGlobal.getClass().getDeclaredField("mDisplayListeners"); | ||
| displayListenersField.setAccessible(true); | ||
| ArrayList<Object> delegates = | ||
| (ArrayList<Object>) displayListenersField.get(displayManagerGlobal); | ||
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| Field listenerField = null; | ||
| ArrayList<DisplayManager.DisplayListener> listeners = new ArrayList<>(); | ||
| for (Object delegate : delegates) { | ||
| if (listenerField == null) { | ||
| listenerField = delegate.getClass().getField("mListener"); | ||
| listenerField.setAccessible(true); | ||
| } | ||
| DisplayManager.DisplayListener listener = | ||
| (DisplayManager.DisplayListener) listenerField.get(delegate); | ||
| listeners.add(listener); | ||
| } | ||
| return listeners; | ||
| } catch (NoSuchFieldException | IllegalAccessException e) { | ||
| Log.w(TAG, "Could not extract WebView's display listeners. " + e); | ||
| return new ArrayList<>(); | ||
| } | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,6 +1,6 @@ | ||
| name: webview_flutter | ||
| description: A Flutter plugin that provides a WebView widget on Android and iOS. | ||
| version: 0.3.11+1 | ||
| author: Flutter Team <[email protected]> | ||
| homepage: https://github.com/flutter/plugins/tree/master/packages/webview_flutter | ||
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😄
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Learned from the best 😄