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    <p>Here's what I came up with today. It's thread-safe, reasonably efficient, and allows for <strong>synchronous Javascript execution from Java for an Android WebView</strong>.</p> <p>Works in Android 2.2 and up. (Requires commons-lang because I need my code snippets passed to eval() as a Javascript string. You could remove this dependency by wrapping the code not in quotation marks, but in <code>function(){}</code>)</p> <p>First, add this to your Javascript file:</p> <pre><code>function evalJsForAndroid(evalJs_index, jsString) { var evalJs_result = ""; try { evalJs_result = ""+eval(jsString); } catch (e) { console.log(e); } androidInterface.processReturnValue(evalJs_index, evalJs_result); } </code></pre> <p>Then, add this to your Android activity:</p> <pre><code>private Handler handler = new Handler(); private final AtomicInteger evalJsIndex = new AtomicInteger(0); private final Map&lt;Integer, String&gt; jsReturnValues = new HashMap&lt;Integer, String&gt;(); private final Object jsReturnValueLock = new Object(); private WebView webView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); webView = (WebView) findViewById(R.id.webView); webView.addJavascriptInterface(new MyJavascriptInterface(this), "androidInterface"); } public String evalJs(final String js) { final int index = evalJsIndex.incrementAndGet(); handler.post(new Runnable() { public void run() { webView.loadUrl("javascript:evalJsForAndroid(" + index + ", " + "\"" + StringEscapeUtils.escapeEcmaScript(js) + "\")"); } }); return waitForJsReturnValue(index, 10000); } private String waitForJsReturnValue(int index, int waitMs) { long start = System.currentTimeMillis(); while (true) { long elapsed = System.currentTimeMillis() - start; if (elapsed &gt; waitMs) break; synchronized (jsReturnValueLock) { String value = jsReturnValues.remove(index); if (value != null) return value; long toWait = waitMs - (System.currentTimeMillis() - start); if (toWait &gt; 0) try { jsReturnValueLock.wait(toWait); } catch (InterruptedException e) { break; } else break; } } Log.e("MyActivity", "Giving up; waited " + (waitMs/1000) + "sec for return value " + index); return ""; } private void processJsReturnValue(int index, String value) { synchronized (jsReturnValueLock) { jsReturnValues.put(index, value); jsReturnValueLock.notifyAll(); } } private static class MyJavascriptInterface { private MyActivity activity; public MyJavascriptInterface(MyActivity activity) { this.activity = activity; } // this annotation is required in Jelly Bean and later: @JavascriptInterface public void processReturnValue(int index, String value) { activity.processJsReturnValue(index, value); } } </code></pre>
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    1. POHow to get return value from javascript in webview of android?
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    1. COThank you for the above code - I adopted it in my Android project. However, there is a trap in it, resulting from bad Java API design. The line: jsReturnValueLock.wait(waitMs - (System.currentTimeMillis() - start)); The value of wait() function argument may sometimes happen to evaluate to 0. And this means "wait infinitely" - I was getting an occasional "no response" errors. I resolved it by testing for: if (elapsed >= waitMS) break; and not calling again System.currentTimeMillis() below, but using the elapsed value. It would be best to edit and fix the above code.
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    2. COWow thanks so much! I was seeing that hang too and never figured out where it was coming from.
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    3. COBut if I run evalJS in button.click listener, etc,. waitForJsReturnValue may cause evalJs() to hang up. So webView.loadUrl() inside handler.post() may not have chance to execute because button.click listener didn't returned.
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