WebViewAssetLoader
public
final
class
WebViewAssetLoader
extends Object
java.lang.Object | |
↳ | androidx.webkit.WebViewAssetLoader |
Helper class to load local files including application's static assets and resources using
http(s):// URLs inside a WebView
class.
Loading local files using web-like URLs instead of "file://"
is desirable as it is
compatible with the Same-Origin policy.
For more context about application's assets and resources and how to normally access them please refer to Android Developer Docs: App resources overview.
This class is expected to be used within
WebViewClient.shouldInterceptRequest(WebView, WebResourceRequest)
, which is invoked on a different
thread than application's main thread. Although instances are themselves thread-safe (and may be
safely constructed on the application's main thread), exercise caution when accessing private
data or the view system.
Using http(s):// URLs to access local resources may conflict with a real website. This means
that local files should only be hosted on domains your organization owns (at paths reserved
for this purpose) or the default domain reserved for this: appassets.androidplatform.net
.
A typical usage would be like:
final WebViewAssetLoader assetLoader = new WebViewAssetLoader.Builder() .addPathHandler("/assets/", new AssetsPathHandler(this)) .build(); webView.setWebViewClient(new WebViewClient() { @Override @RequiresApi(21) public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) { return assetLoader.shouldInterceptRequest(request.getUrl()); } @Override @SuppressWarnings("deprecation") // for API < 21 public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) { return assetLoader.shouldInterceptRequest(Uri.parse(request)); } }); WebSettings webViewSettings = webView.getSettings(); // Setting this off for security. Off by default for SDK versions >= 16. webViewSettings.setAllowFileAccessFromFileURLs(false); // Off by default, deprecated for SDK versions >= 30. webViewSettings.setAllowUniversalAccessFromFileURLs(false); // Keeping these off is less critical but still a good idea, especially if your app is not // using file:// or content:// URLs. webViewSettings.setAllowFileAccess(false); webViewSettings.setAllowContentAccess(false); // Assets are hosted under http(s)://appassets.androidplatform.net/assets/... . // If the application's assets are in the "main/assets" folder this will read the file // from "main/assets/www/index.html" and load it as if it were hosted on: // https://appassets.androidplatform.net/assets/www/index.html webview.loadUrl("https://appassets.androidplatform.net/assets/www/index.html");
Summary
Nested classes | |
---|---|
class |
WebViewAssetLoader.AssetsPathHandler
Handler class to open a file from assets directory in the application APK. |
class |
WebViewAssetLoader.Builder
A builder class for constructing |
class |
WebViewAssetLoader.InternalStoragePathHandler
Handler class to open files from application internal storage. |
interface |
WebViewAssetLoader.PathHandler
A handler that produces responses for a registered path. |
class |
WebViewAssetLoader.ResourcesPathHandler
Handler class to open a file from resources directory in the application APK. |
Constants | |
---|---|
String |
DEFAULT_DOMAIN
An unused domain reserved for Android applications to intercept requests for app assets. |
Public methods | |
---|---|
WebResourceResponse
|
shouldInterceptRequest(Uri url)
Attempt to resolve the |
Inherited methods | |
---|---|
Constants
DEFAULT_DOMAIN
public static final String DEFAULT_DOMAIN
An unused domain reserved for Android applications to intercept requests for app assets.
It is used by default unless the user specified a different domain.
Constant Value: "appassets.androidplatform.net"
Public methods
shouldInterceptRequest
public WebResourceResponse shouldInterceptRequest (Uri url)
Attempt to resolve the url
to an application resource or asset, and return
a WebResourceResponse
for the content.
This method should be invoked from within
WebViewClient.shouldInterceptRequest(android.webkit.WebView, String)
.
Parameters | |
---|---|
url |
Uri : the URL to process. |
Returns | |
---|---|
WebResourceResponse |
WebResourceResponse if the request URL matches a registered URL,
null otherwise.
|
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Last updated 2020-09-30 UTC.