我一直在努力解决WebView中的JavaScript同步调用问题（带有返回值），并试图缩小原因的地点和原因工作。似乎是WebView线程在主线程等待来自它的响应时阻塞 - 因为WebView在一个单独的线程上运行，所以不应该这样。 / p>
我已经把这个小样本放在一起，相当清楚地展示了它（我希望）：
main.xml中：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:weightSum="1">
<WebView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/webView"/>
</LinearLayout>
MyActivity.java：
package com.example.myapp;
import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.JavascriptInterface;
import android.webkit.WebViewClient;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
public class MyActivity extends Activity {
public final static String TAG = "MyActivity";
private WebView webView;
private JSInterface JS;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
webView = (WebView)findViewById(R.id.webView);
JS = new JSInterface();
webView.addJavascriptInterface(JS, JS.getInterfaceName());
WebSettings settings = webView.getSettings();
settings.setJavaScriptEnabled(true);
webView.setWebViewClient(new WebViewClient() {
public void onPageFinished(WebView view, String url) {
Log.d(TAG, JS.getEval("test()"));
}
});
webView.loadData("<script>function test() {JSInterface.log(\"returning Success\"); return 'Success';}</script>Test", "text/html", "UTF-8");
}
private class JSInterface {
private static final String TAG = "JSInterface";
private final String interfaceName = "JSInterface";
private CountDownLatch latch;
private String returnValue;
public JSInterface() {
}
public String getInterfaceName() {
return interfaceName;
}
// JS-side functions can call JSInterface.log() to log to logcat
@JavascriptInterface
public void log(String str) {
// log() gets called from Javascript
Log.i(TAG, str);
}
// JS-side functions will indirectly call setValue() via getEval()'s try block, below
@JavascriptInterface
public void setValue(String value) {
// setValue() receives the value from Javascript
Log.d(TAG, "setValue(): " + value);
returnValue = value;
latch.countDown();
}
// getEval() is for when you need to evaluate JS code and get the return value back
public String getEval(String js) {
Log.d(TAG, "getEval(): " + js);
returnValue = null;
latch = new CountDownLatch(1);
final String code = interfaceName
+ ".setValue(function(){try{return " + js
+ "+\"\";}catch(js_eval_err){return '';}}());";
Log.d(TAG, "getEval(): " + code);
// It doesn't actually matter which one we use; neither works:
if (Build.VERSION.SDK_INT >= 19)
webView.evaluateJavascript(code, null);
else
webView.loadUrl("javascript:" + code);
// The problem is that latch.await() appears to block, not allowing the JavaBridge
// thread to run -- i.e., to call setValue() and therefore latch.countDown() --
// so latch.await() always runs until it times out and getEval() returns ""
try {
// Set a 4 second timeout for the worst/longest possible case
latch.await(4, TimeUnit.SECONDS);
} catch (InterruptedException e) {
Log.e(TAG, "InterruptedException");
}
if (returnValue == null) {
Log.i(TAG, "getEval(): Timed out waiting for response");
returnValue = "";
}
Log.d(TAG, "getEval() = " + returnValue);
return returnValue;
}
// eval() is for when you need to run some JS code and don't care about any return value
public void eval(String js) {
// No return value
Log.d(TAG, "eval(): " + js);
if (Build.VERSION.SDK_INT >= 19)
webView.evaluateJavascript(js, null);
else
webView.loadUrl("javascript:" + js);
}
}
}
运行时，会产生以下结果：
Emulator Nexus 5 API 23:
05-25 13:34:46.222 16073-16073/com.example.myapp D/JSInterface: getEval(): test()
05-25 13:34:50.224 16073-16073/com.example.myapp I/JSInterface: getEval(): Timed out waiting for response
05-25 13:34:50.224 16073-16073/com.example.myapp D/JSInterface: getEval() =
05-25 13:34:50.225 16073-16073/com.example.myapp I/Choreographer: Skipped 239 frames! The application may be doing too much work on its main thread.
05-25 13:34:50.235 16073-16150/com.example.myapp I/JSInterface: returning Success
05-25 13:34:50.237 16073-16150/com.example.myapp D/JSInterface: setValue(): Success
（16073是＆＃39;主要＆＃39 ;; 16150是＆＃39; JavaBridge＆＃39;）
正如您所看到的，主线程超时等待WebView调用setValue()，直到latch.await()超时且主线程执行已经超时才会调用Emulator Nexus S API 14:
05-25 13:37:15.225 19458-19458/com.example.myapp D/JSInterface: getEval(): test()
05-25 13:37:15.235 19458-19543/com.example.myapp I/JSInterface: returning Success
05-25 13:37:15.235 19458-19543/com.example.myapp D/JSInterface: setValue(): Success
05-25 13:37:15.235 19458-19458/com.example.myapp D/JSInterface: getEval() = Success
05-25 13:37:15.235 19458-19458/com.example.myapp D/MyActivity: Success
继续进行。
有趣的是，尝试使用较早的API级别：
getEval()（19458＆＃39; main＆＃39 ;; 19543＆＃39; JavaBridge＆＃39;）
事情按顺序正常工作，WebView导致setValue()调用latch.await()，然后line = line.replaceAll("&", "&")退出String fileData = "";
String line = "";
BufferedReader br=new BufferedReader(new InputStreamReader(is));
while((line = br.readLine()) != null)
{
line = line.replace("&", "&");
fileData += line;
fileData += "\n";
}
parser.setInput(new StringReader(fileData));
，然后超时（正如您所期望的那样） /希望）。
（我还尝试使用更早的API级别，但事情已经崩溃了，因为据我所知，2.3.3中的模拟器错误从未得到修复。）
所以我有点失落。在挖掘中，这似乎是正确的做事方法。它肯定似乎就像正确的方法，因为它在API级别14上正常工作。但是它在以后的版本上失败了 - 我在5.1和6.0上测试没有成功。< / p>
答案 0 :(得分：1)
了解有关使用Android 4.4迁移WebView的更多信息。 See description on Android Docs我认为你需要使用另一种方法来娱乐你的JS动作。
例如，基于该文档 - Running JS Async在当前显示的页面的上下文中异步评估JavaScript。如果非null，| resultCallback |将使用该执行返回的任何结果调用。必须在UI线程上调用此方法，并且将在UI线程上进行回调。