1、问题
使用webview加载网页，在应用运行时，报了如下错误：
android.webkit.WebViewFactory$MissingWebViewPackageException: Failed to load WebView provider: No WebView installed
2、分析
通过查看项目的修改记录，确实安装了WebView。打开cmd，执行adb shell "pm list packages | grep webview"该命令，可以看到安装的webview的包名。如图：
C:\Users\ABC1314>adb shell "pm list packages | grep webview"
package:com.google.android.webview
3、解决
系统是通过SystemImpl.java获取config_webview_packages.xml文件中定义的WebView
路径：frameworks/base/services/core/java/com/android/server/webkit/SystemImpl.java
private SystemImpl() {int numFallbackPackages = 0;int numAvailableByDefaultPackages = 0;XmlResourceParser parser = null;List<WebViewProviderInfo> webViewProviders = new ArrayList<WebViewProviderInfo>();try {parser = AppGlobals.getInitialApplication().getResources().getXml(com.android.internal.R.xml.config_webview_packages);XmlUtils.beginDocument(parser, TAG_START);while(true) {XmlUtils.nextElement(parser);String element = parser.getName();if (element == null) {break;}if (element.equals(TAG_WEBVIEW_PROVIDER)) {String packageName = parser.getAttributeValue(null, TAG_PACKAGE_NAME);if (packageName == null) {throw new AndroidRuntimeException("WebView provider in framework resources missing package name");}String description = parser.getAttributeValue(null, TAG_DESCRIPTION);if (description == null) {throw new AndroidRuntimeException("WebView provider in framework resources missing description");}boolean availableByDefault = "true".equals(parser.getAttributeValue(null, TAG_AVAILABILITY));boolean isFallback = "true".equals(parser.getAttributeValue(null, TAG_FALLBACK));WebViewProviderInfo currentProvider = new WebViewProviderInfo(packageName, description, availableByDefault, isFallback,readSignatures(parser));if (currentProvider.isFallback) {numFallbackPackages++;if (!currentProvider.availableByDefault) {throw new AndroidRuntimeException("Each WebView fallback package must be available by default.");}if (numFallbackPackages > 1) {throw new AndroidRuntimeException("There can be at most one WebView fallback package.");}}if (currentProvider.availableByDefault) {numAvailableByDefaultPackages++;}webViewProviders.add(currentProvider);}else {Log.e(TAG, "Found an element that is not a WebView provider");}}} catch (XmlPullParserException | IOException e) {throw new AndroidRuntimeException("Error when parsing WebView config " + e);} finally {if (parser != null) parser.close();}if (numAvailableByDefaultPackages == 0) {throw new AndroidRuntimeException("There must be at least one WebView package "+ "that is available by default");}mWebViewProviderPackages =webViewProviders.toArray(new WebViewProviderInfo[webViewProviders.size()]);}
查看frameworks/base/core/res/res/xml/config_webview_packages.xml文件中对使用的webview进行声明：如下
<!-- The default WebView implementation --><webviewprovider description="Android WebView" packageName="com.android.webview" availableByDefault="true"></webviewprovider>
可以看到，在该文件中声明的webview的包名是：com.android.webview，而我们通过adb命令看到系统安装的webview包名是com.google.android.webview，二者不同，导致了无法找到webview.
只需要在该xml文件中，将我们安装的webview添加进去即可。
<webviewproviders><webviewprovider description="Google WebView" packageName="com.google.android.webview" availableByDefault="true"></webviewprovider><webviewprovider description="Trichromelibrary" packageName="com.google.android.trichromelibrary" availableByDefault="true"></webviewprovider><!-- The default WebView implementation --><webviewprovider description="Android WebView" packageName="com.android.webview" availableByDefault="true"></webviewprovider>
</webviewproviders>
