这是一种利用Android的JavaScript hooks功能检测URL何时加载的新颖方法。使用此模式，我们利用JavaScript对文档状态的了解来在Android运行时内生成本机方法调用。这些JavaScript可访问的调用可以使用@JavaScriptInterface注释。
实现需要，我们称之为setJavaScriptEnabled(true)上WebView的设置，所以它可能不适合取决于应用程序的需求，如安全问题。
src / io / github / cawfree / webviewcallback / MainActivity.java （果冻豆，API级别16）
package io.github.cawfree.webviewcallback;
/**
* Created by Alex Thomas (@Cawfree), 30/03/2017.
**/
import android.net.http.SslError;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.JavascriptInterface;
import android.webkit.SslErrorHandler;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;
/** An Activity demonstrating how to introduce a callback mechanism into Android's WebView. */
public class MainActivity extends AppCompatActivity {
/* Static Declarations. */
private static final String HOOK_JS = "Android";
private static final String URL_TEST = "http://www.zonal.co.uk/";
private static final String URL_PREPARE_WEBVIEW = "";
/* Member Variables. */
private WebView mWebView = null;
/** Create the Activity. */
@Override protected final void onCreate(final Bundle pSavedInstanceState) {
// Initialize the parent definition.
super.onCreate(pSavedInstanceState);
// Set the Content View.
this.setContentView(R.layout.activity_main);
// Fetch the WebView.
this.mWebView = (WebView)this.findViewById(R.id.webView);
// Enable JavaScript.
this.getWebView().getSettings().setJavaScriptEnabled(true);
// Define the custom WebClient. (Here I'm just suppressing security errors, since older Android devices struggle with TLS.)
this.getWebView().setWebViewClient(new WebViewClient() { @Override public final void onReceivedSslError(final WebView pWebView, final SslErrorHandler pSslErrorHandler, final SslError pSslError) { pSslErrorHandler.proceed(); } });
// Define the WebView JavaScript hook.
this.getWebView().addJavascriptInterface(this, MainActivity.HOOK_JS);
// Make this initial call to prepare JavaScript execution.
this.getWebView().loadUrl(MainActivity.URL_PREPARE_WEBVIEW);
}
/** When the Activity is Resumed. */
@Override protected final void onPostResume() {
// Handle as usual.
super.onPostResume();
// Load the URL as usual.
this.getWebView().loadUrl(MainActivity.URL_TEST);
// Use JavaScript to embed a hook to Android's MainActivity. (The onExportPageLoaded() function implements the callback, whilst we add some tests for the state of the WebPage so as to infer when to export the event.)
this.getWebView().loadUrl("javascript:" + "function onExportPageLoaded() { " + MainActivity.HOOK_JS + ".onPageLoaded(); }" + "if(document.readyState === 'complete') { onExportPageLoaded(); } else { window.addEventListener('onload', function () { onExportPageLoaded(); }, false); }");
}
/** Javascript-accessible callback for declaring when a page has loaded. */
@JavascriptInterface @SuppressWarnings("unused") public final void onPageLoaded() {
// Display the Message.
Toast.makeText(this, "Page has loaded!", Toast.LENGTH_SHORT).show();
}
/* Getters. */
public final WebView getWebView() {
return this.mWebView;
}
}
RES /布局/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<WebView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/webView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
本质上，我们将附加一个额外的JavaScript函数，该函数用于测试文档的状态。如果已加载，我们将onPageLoaded()在Android的中启动一个自定义事件MainActivity；否则，我们会使用来注册一个事件监听器，以在页面准备好后更新Android window.addEventListener('onload', ...);。
由于我们是在调用之后添加该脚本的this.getWebView().loadURL("")，因此我们根本不需要“监听”事件，因为我们只有通过连续调用来添加JavaScript钩子的机会，loadURL，一旦页面已加载。