webview_flutter select 閃退

    在安卓版本打開網頁之後，頁面有select點擊，整個程序就閃退。在網上查了這篇文章解決辦法，以下記錄完整的過程.

dependencies:

webview_flutter: ^0.3.19+9

自己安裝flutter sdk的位置，這裏是D盤

D:\Program Files\flutter\.pub-cache\hosted\pub.flutter-io.cn\webview_flutter-0.3.19+9\android\src\main\java\io\flutter\plugins\webviewflutter

打開這個文件   FlutterWebView.java

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.plugins.webviewflutter;

import android.annotation.TargetApi;
import android.content.Context;
import android.hardware.display.DisplayManager;
import android.os.Build;
import android.os.Handler;
import android.view.View;
import android.webkit.WebStorage;
import android.webkit.WebViewClient;
import io.flutter.plugin.common.BinaryMessenger;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
import io.flutter.plugin.common.MethodChannel.Result;
import io.flutter.plugin.platform.PlatformView;
import java.util.Collections;
import java.util.List;
import java.util.Map;
//**添加這兩個
import android.app.Activity;
import io.flutter.app.FlutterApplication;

public class FlutterWebView implements PlatformView, MethodCallHandler {
  private static final String JS_CHANNEL_NAMES_FIELD = "javascriptChannelNames";
  private final InputAwareWebView webView;
  private final MethodChannel methodChannel;
  private final FlutterWebViewClient flutterWebViewClient;
  private final Handler platformThreadHandler;
  
  @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
  @SuppressWarnings("unchecked")
  FlutterWebView(
      //把final 取消
  	  Context context,
      BinaryMessenger messenger,
      int id,
      Map<String, Object> params,
      View containerView) {
  		
        //添加代碼開始
	    Context appContext = context.getApplicationContext();
	    if (appContext instanceof FlutterApplication) {
	      Activity currentActivity = ((FlutterApplication) appContext).getCurrentActivity();

	      if (currentActivity != null) {
	        //獲取當前context所對應的activity
	        context = currentActivity;
	      }
	    }
         //添加代碼結束

    DisplayListenerProxy displayListenerProxy = new DisplayListenerProxy();
    DisplayManager displayManager =
        (DisplayManager) context.getSystemService(Context.DISPLAY_SERVICE);
    displayListenerProxy.onPreWebViewInitialization(displayManager);
    webView = new InputAwareWebView(context, containerView);
    displayListenerProxy.onPostWebViewInitialization(displayManager);

    platformThreadHandler = new Handler(context.getMainLooper());
    // Allow local storage.
    webView.getSettings().setDomStorageEnabled(true);
    webView.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);

    methodChannel = new MethodChannel(messenger, "plugins.flutter.io/webview_" + id);
    methodChannel.setMethodCallHandler(this);

    flutterWebViewClient = new FlutterWebViewClient(methodChannel);
    applySettings((Map<String, Object>) params.get("settings"));

    if (params.containsKey(JS_CHANNEL_NAMES_FIELD)) {
      registerJavaScriptChannelNames((List<String>) params.get(JS_CHANNEL_NAMES_FIELD));
    }

    updateAutoMediaPlaybackPolicy((Integer) params.get("autoMediaPlaybackPolicy"));
    if (params.containsKey("userAgent")) {
      String userAgent = (String) params.get("userAgent");
      updateUserAgent(userAgent);
    }
    if (params.containsKey("initialUrl")) {
      String url = (String) params.get("initialUrl");
      webView.loadUrl(url);
    }
  }

  @Override
  public View getView() {
    return webView;
  }

  // @Override
  // This is overriding a method that hasn't rolled into stable Flutter yet. Including the
  // annotation would cause compile time failures in versions of Flutter too old to include the new
  // method. However leaving it raw like this means that the method will be ignored in old versions
  // of Flutter but used as an override anyway wherever it's actually defined.
  // TODO(mklim): Add the @Override annotation once flutter/engine#9727 rolls to stable.
  public void onInputConnectionUnlocked() {
    webView.unlockInputConnection();
  }

  // @Override
  // This is overriding a method that hasn't rolled into stable Flutter yet. Including the
  // annotation would cause compile time failures in versions of Flutter too old to include the new
  // method. However leaving it raw like this means that the method will be ignored in old versions
  // of Flutter but used as an override anyway wherever it's actually defined.
  // TODO(mklim): Add the @Override annotation once flutter/engine#9727 rolls to stable.
  public void onInputConnectionLocked() {
    webView.lockInputConnection();
  }

  // @Override
  // This is overriding a method that hasn't rolled into stable Flutter yet. Including the
  // annotation would cause compile time failures in versions of Flutter too old to include the new
  // method. However leaving it raw like this means that the method will be ignored in old versions
  // of Flutter but used as an override anyway wherever it's actually defined.
  // TODO(mklim): Add the @Override annotation once stable passes v1.10.9.
  public void onFlutterViewAttached(View flutterView) {
    webView.setContainerView(flutterView);
  }

  // @Override
  // This is overriding a method that hasn't rolled into stable Flutter yet. Including the
  // annotation would cause compile time failures in versions of Flutter too old to include the new
  // method. However leaving it raw like this means that the method will be ignored in old versions
  // of Flutter but used as an override anyway wherever it's actually defined.
  // TODO(mklim): Add the @Override annotation once stable passes v1.10.9.
  public void onFlutterViewDetached() {
    webView.setContainerView(null);
  }

  @Override
  public void onMethodCall(MethodCall methodCall, Result result) {
    switch (methodCall.method) {
      case "loadUrl":
        loadUrl(methodCall, result);
        break;
      case "updateSettings":
        updateSettings(methodCall, result);
        break;
      case "canGoBack":
        canGoBack(result);
        break;
      case "canGoForward":
        canGoForward(result);
        break;
      case "goBack":
        goBack(result);
        break;
      case "goForward":
        goForward(result);
        break;
      case "reload":
        reload(result);
        break;
      case "currentUrl":
        currentUrl(result);
        break;
      case "evaluateJavascript":
        evaluateJavaScript(methodCall, result);
        break;
      case "addJavascriptChannels":
        addJavaScriptChannels(methodCall, result);
        break;
      case "removeJavascriptChannels":
        removeJavaScriptChannels(methodCall, result);
        break;
      case "clearCache":
        clearCache(result);
        break;
      case "getTitle":
        getTitle(result);
        break;
      default:
        result.notImplemented();
    }
  }

  @SuppressWarnings("unchecked")
  private void loadUrl(MethodCall methodCall, Result result) {
    Map<String, Object> request = (Map<String, Object>) methodCall.arguments;
    String url = (String) request.get("url");
    Map<String, String> headers = (Map<String, String>) request.get("headers");
    if (headers == null) {
      headers = Collections.emptyMap();
    }
    webView.loadUrl(url, headers);
    result.success(null);
  }

  private void canGoBack(Result result) {
    result.success(webView.canGoBack());
  }

  private void canGoForward(Result result) {
    result.success(webView.canGoForward());
  }

  private void goBack(Result result) {
    if (webView.canGoBack()) {
      webView.goBack();
    }
    result.success(null);
  }

  private void goForward(Result result) {
    if (webView.canGoForward()) {
      webView.goForward();
    }
    result.success(null);
  }

  private void reload(Result result) {
    webView.reload();
    result.success(null);
  }

  private void currentUrl(Result result) {
    result.success(webView.getUrl());
  }

  @SuppressWarnings("unchecked")
  private void updateSettings(MethodCall methodCall, Result result) {
    applySettings((Map<String, Object>) methodCall.arguments);
    result.success(null);
  }

  @TargetApi(Build.VERSION_CODES.KITKAT)
  private void evaluateJavaScript(MethodCall methodCall, final Result result) {
    String jsString = (String) methodCall.arguments;
    if (jsString == null) {
      throw new UnsupportedOperationException("JavaScript string cannot be null");
    }
    webView.evaluateJavascript(
        jsString,
        new android.webkit.ValueCallback<String>() {
          @Override
          public void onReceiveValue(String value) {
            result.success(value);
          }
        });
  }

  @SuppressWarnings("unchecked")
  private void addJavaScriptChannels(MethodCall methodCall, Result result) {
    List<String> channelNames = (List<String>) methodCall.arguments;
    registerJavaScriptChannelNames(channelNames);
    result.success(null);
  }

  @SuppressWarnings("unchecked")
  private void removeJavaScriptChannels(MethodCall methodCall, Result result) {
    List<String> channelNames = (List<String>) methodCall.arguments;
    for (String channelName : channelNames) {
      webView.removeJavascriptInterface(channelName);
    }
    result.success(null);
  }

  private void clearCache(Result result) {
    webView.clearCache(true);
    WebStorage.getInstance().deleteAllData();
    result.success(null);
  }

  private void getTitle(Result result) {
    result.success(webView.getTitle());
  }

  private void applySettings(Map<String, Object> settings) {
    for (String key : settings.keySet()) {
      switch (key) {
        case "jsMode":
          updateJsMode((Integer) settings.get(key));
          break;
        case "hasNavigationDelegate":
          final boolean hasNavigationDelegate = (boolean) settings.get(key);

          final WebViewClient webViewClient =
              flutterWebViewClient.createWebViewClient(hasNavigationDelegate);

          webView.setWebViewClient(webViewClient);
          break;
        case "debuggingEnabled":
          final boolean debuggingEnabled = (boolean) settings.get(key);

          webView.setWebContentsDebuggingEnabled(debuggingEnabled);
          break;
        case "gestureNavigationEnabled":
          break;
        case "userAgent":
          updateUserAgent((String) settings.get(key));
          break;
        default:
          throw new IllegalArgumentException("Unknown WebView setting: " + key);
      }
    }
  }

  private void updateJsMode(int mode) {
    switch (mode) {
      case 0: // disabled
        webView.getSettings().setJavaScriptEnabled(false);
        break;
      case 1: // unrestricted
        webView.getSettings().setJavaScriptEnabled(true);
        break;
      default:
        throw new IllegalArgumentException("Trying to set unknown JavaScript mode: " + mode);
    }
  }

  private void updateAutoMediaPlaybackPolicy(int mode) {
    // This is the index of the AutoMediaPlaybackPolicy enum, index 1 is always_allow, for all
    // other values we require a user gesture.
    boolean requireUserGesture = mode != 1;
    webView.getSettings().setMediaPlaybackRequiresUserGesture(requireUserGesture);
  }

  private void registerJavaScriptChannelNames(List<String> channelNames) {
    for (String channelName : channelNames) {
      webView.addJavascriptInterface(
          new JavaScriptChannel(methodChannel, channelName, platformThreadHandler), channelName);
    }
  }

  private void updateUserAgent(String userAgent) {
    webView.getSettings().setUserAgentString(userAgent);
  }

  @Override
  public void dispose() {
    methodChannel.setMethodCallHandler(null);
    webView.dispose();
    webView.destroy();
  }
}