How to determine when Android WebView is completely done loading?

When using Android WebView, you can determine when a page has fully loaded through several methods. The most common approach involves utilizing callback methods within the WebViewClient class to monitor loading events. Below is a concrete example:

java
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MyWebViewClient extends WebViewClient {
    @Override
    public void onPageFinished(WebView view, String url) {
        // This method is invoked when the page has fully loaded.
        super.onPageFinished(view, url);

        // Add your code here to handle logic after the page has loaded.
        // For example, hide the loading animation and update the UI.
    }

    @Override
    public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
        // This method is called when page loading encounters an error.
        super.onReceivedError(view, errorCode, description, failingUrl);

        // Add your code here to handle error scenarios.
        // For example, display an error message and provide a retry button.
    }

    // If your application supports Android API level 23 or higher, use this method to handle HTTP errors.
    @Override
    public void onReceivedHttpError(WebView view, WebResourceRequest request, WebResourceResponse errorResponse) {
        super.onReceivedHttpError(view, request, errorResponse);

        // Add your code here to handle HTTP errors.
    }
}

// Then, configure your WebView to use the WebViewClient.
WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.setWebViewClient(new MyWebViewClient());

// Load a webpage
myWebView.loadUrl("http://www.example.com");

In the above code, the onPageFinished method is invoked after the page has finished loading. This typically indicates that the page has fully loaded, with all resources (such as images, JavaScript scripts, etc.) downloaded and rendered within the WebView. However, it's important to note that if the page contains asynchronous requests or subsequent JavaScript processing, the invocation of onPageFinished does not necessarily mean all content has been loaded; further verification may be necessary.

To improve detection accuracy, you might need to add JavaScript event listeners to communicate with the WebView's Java component, confirming that all dynamic content has been loaded. This can be achieved by using the WebView's addJavascriptInterface method to establish a bridge between JavaScript and Android Java code.

Here is an example of adding a JavaScript interface to notify Android when the page has fully loaded:

java
import android.webkit.JavascriptInterface;

public class WebAppInterface {
    @JavascriptInterface
    public void notifyPageLoaded() {
        // This method is called when the JavaScript portion of the page has finished executing.
        // Add your code here to handle logic after the page has fully loaded.
    }
}

// Add the JavaScript interface to the WebView configuration
myWebView.addJavascriptInterface(new WebAppInterface(), "Android");

// In the page's JavaScript section, call the Android method when all content is loaded.
// Add the following code in JavaScript's window.onload or similar events:
window.Android.notifyPageLoaded();

In summary, determining when Android WebView has fully loaded requires combining the use of callback methods within WebViewClient to monitor basic loading events, and optionally using JavaScript interfaces for more precise loading completion signals.