標籤：
Android提供了一個很強大的WebView控制項用來處理Web網頁，而在網頁中，JavaScript又是一個很舉足輕重的指令碼。本文將介紹如何?Java代碼和Javascript代碼的相互調用。
如何?實現Java和js互動十分便捷。通常只需要以下幾步。
為了便於講解，先貼出全部代碼
Java代碼
package com.example.javajsinteractiondemo;import android.annotation.SuppressLint;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.view.Menu;import android.webkit.JavascriptInterface;import android.webkit.WebChromeClient;import android.webkit.WebSettings;import android.webkit.WebView;import android.webkit.WebViewClient;import android.widget.Toast;public class MainActivity extends Activity { private static final String LOGTAG = "MainActivity"; @SuppressLint("JavascriptInterface") @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); final WebView myWebView = (WebView) findViewById(R.id.myWebView); WebSettings settings = myWebView.getSettings(); settings.setJavaScriptEnabled(true); myWebView.addJavascriptInterface(new JsInteration(), "control"); myWebView.setWebChromeClient(new WebChromeClient() {}); myWebView.setWebViewClient(new WebViewClient() { @Override public void onPageFinished(WebView view, String url) { super.onPageFinished(view, url); testMethod(myWebView); } }); myWebView.loadUrl("file:///android_asset/js_java_interaction.html"); } private void testMethod(WebView webView) { String call = "javascript:sayHello()"; call = "javascript:alertMessage("" + "content" + "")"; call = "javascript:toastMessage("" + "content" + "")"; call = "javascript:sumToJava(1,2)"; webView.loadUrl(call); } public class JsInteration { @JavascriptInterface public void toastMessage(String message) { Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG).show(); } @JavascriptInterface public void onSumResult(int result) { Log.i(LOGTAG, "onSumResult result=" + result); } }}前端網頁代碼
<html><script type="text/javascript"> function sayHello() { alert("Hello") } function alertMessage(message) { alert(message) } function toastMessage(message) { window.control.toastMessage(message) } function sumToJava(number1, number2){ window.control.onSumResult(number1 + number2) }</script>Java-Javascript Interaction In Android</html>調用樣本js調用Java調用格式為window.jsInterfaceName.methodName(parameterValues) 此例中我們使用的是control作為注入介面名稱。
function toastMessage(message) { window.control.toastMessage(message)}function sumToJava(number1, number2){ window.control.onSumResult(number1 + number2)}Java調用JSwebView調用js的基本格式為webView.loadUrl(“javascript:methodName(parameterValues)”)
調用js無參無傳回值函數String call = "javascript:sayHello()";webView.loadUrl(call);調用js有參無傳回值函數
注意對於字串作為參數值需要進行轉義雙引號。
String call = "javascript:alertMessage("" + "content" + "")";webView.loadUrl(call);調用js有參數有傳回值的函數Android在4.4之前並沒有提供直接調用js函數並擷取值的方法，所以在此之前，常用的思路是 java調用js方法，js方法執行完畢，再次調用java代碼將值返回。
1.Java調用js代碼
String call = "javascript:sumToJava(1,2)";webView.loadUrl(call);
2.js函數處理，並將結果通過調用java方法返回
function sumToJava(number1, number2){ window.control.onSumResult(number1 + number2)}3.Java在回調方法中擷取js函數傳回值
@JavascriptInterfacepublic void onSumResult(int result) { Log.i(LOGTAG, "onSumResult result=" + result);}4.4處理Android 4.4之後使用evaluateJavascript即可。這裡展示一個簡單的互動樣本 具有傳回值的js方法
function getGreetings() { return 1;}java代碼時用evaluateJavascript方法調用
private void testEvaluateJavascript(WebView webView) { webView.evaluateJavascript("getGreetings()", new ValueCallback<String>() { @Override public void onReceiveValue(String value) { Log.i(LOGTAG, "onReceiveValue value=" + value); }});}輸出結果
I/MainActivity( 1432): onReceiveValue value=1
注意
你應該是沒有設定WebChromeClient,按照以下代碼設定
myWebView.setWebChromeClient(new WebChromeClient() {});Uncaught ReferenceError: functionName is not defined問題出現原因，網頁的js代碼沒有載入完成，就調用了js方法。解決方案是在網頁載入完成之後調用js方法
myWebView.setWebViewClient(new WebViewClient() { @Override public void onPageFinished(WebView view, String url) { super.onPageFinished(view, url); //在這裡執行你想調用的js函數 }});Uncaught TypeError: Object [object Object] has no method安全限制問題如果只在4.2版本以上的機器出問題，那麼就是系統處於安全限制的問題了。Android文檔這樣說的
Caution: If you’ve set your targetSdkVersion to 17 or higher, you must add the @JavascriptInterface annotation to any method that you want available your web page code (the method must also be public). If you do not provide the annotation, then the method will not accessible by your web page when running on Android 4.2 or higher.
中文大意為
兩種解決方案警告：如果你的程式目標平台是17或者是更高，你必須要在暴露給網頁可調用的方法（這個方法必須是公開的）加上@JavascriptInterface注釋。如果你不這樣做的話，在4.2以以後的平台上，網頁無法訪問到你的方法。
注，建立@JavascriptInterface代碼
public @interface JavascriptInterface {}代碼混淆問題如果在沒有混淆的版本運行正常，在混淆後的版本的代碼運行錯誤，並提示Uncaught TypeError: Object [object Object] has no method，那就是你沒有做混淆例外處理。 在混淆檔案加入類似這樣的代碼
-keep class com.example.javajsinteractiondemo$JsInteration { *;}All WebView methods must be called on the same thread過濾日誌曾發現過這個問題。
E/StrictMode( 1546): java.lang.Throwable: A WebView method was called on thread ＇JavaBridge＇. All WebView methods must be called on the same thread. (Expected Looper Looper (main, tid 1) {528712d4} called on Looper (JavaBridge, tid 121) {52b6678c}, FYI main Looper is Looper (main, tid 1) {528712d4})E/StrictMode( 1546): at android.webkit.WebView.checkThread(WebView.java:2063)E/StrictMode( 1546): at android.webkit.WebView.loadUrl(WebView.java:794)E/StrictMode( 1546): at com.xxx.xxxx.xxxx.xxxx.xxxxxxx$JavaScriptInterface.onCanGoBackResult(xxxx.java:96)E/StrictMode( 1546): at com.android.org.chromium.base.SystemMessageHandler.nativeDoRunLoopOnce(Native Method)E/StrictMode( 1546): at com.android.org.chromium.base.SystemMessageHandler.handleMessage(SystemMessageHandler.java:27)E/StrictMode( 1546): at android.os.Handler.dispatchMessage(Handler.java:102)E/StrictMode( 1546): at android.os.Looper.loop(Looper.java:136)E/StrictMode( 1546): at android.os.HandlerThread.run(HandlerThread.java:61)在js調用後的Java回調線程並不是主線程。如列印日誌可驗證
ThreadInfo=Thread[WebViewCoreThread,5,main]
解決上述的異常，將webview操作放在主線程中即可。
webView.post(new Runnable() { @Override public void run() { webView.loadUrl(YOUR_URL). }});
Android WebView與JS互動
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