How to get return value from javascript in webview

2019-01-02 22:35发布

站内问答 / Android
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I want to get a return value from Javascript in Android. I can do it with iPhone, but I can't with Android. I used loadUrl, but it returned void instead of an object. Can anybody help me? Thanks.

7条回答
甜甜的少女心
2楼-- · 2019-01-02 23:02

Use addJavascriptInterface() to add a Java object to the Javascript environment. Have your Javascript call a method on that Java object to supply its "return value".

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兄弟一词,经得起流年.
3楼-- · 2019-01-02 23:05

On API 19+, the best way to do this is to call evaluateJavascript on your WebView:

webView.evaluateJavascript("foo.bar()", new ValueCallback<String>() {
    @Override public void onReceiveValue(String value) {
        // value is the result returned by the Javascript as JSON
    }
});

Related answer with more detail: https://stackoverflow.com/a/20377857

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唯我独甜
4楼-- · 2019-01-02 23:13

Here's a hack on how you can accomplish it:

Add this Client to your WebView:

final class MyWebChromeClient extends WebChromeClient {
        @Override
        public boolean onJsAlert(WebView view, String url, String message, JsResult result) {
            Log.d("LogTag", message);
            result.confirm();
            return true;
        }
    }

Now in your javascript call do:

webView.loadUrl("javascript:alert(functionThatReturnsSomething)");

Now in the onJsAlert call "message" will contain the returned value.

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做自己的国王
5楼-- · 2019-01-02 23:13

As an alternative variant that uses a custom scheme:

MainActivity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            WebView.setWebContentsDebuggingEnabled(true);
        }

        final WebView webview = new CustomWebView(this);

        setContentView(webview);

        webview.loadUrl("file:///android_asset/customPage.html");

        webview.postDelayed(new Runnable() {
            @Override
            public void run() {

                //Android -> JS
                webview.loadUrl("javascript:showToast()");
            }
        }, 1000);
    }
}

CustomWebView

public class CustomWebView extends WebView {
    public CustomWebView(Context context) {
        super(context);

        setup();
    }

    @SuppressLint("SetJavaScriptEnabled")
    private void setup() {
        setWebViewClient(new AdWebViewClient());

        getSettings().setJavaScriptEnabled(true);

    }

    private class AdWebViewClient extends WebViewClient {

        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {

            if (url.startsWith("customschema://")) {
                //parse uri
                Toast.makeText(CustomWebView.this.getContext(), "event was received", Toast.LENGTH_SHORT).show();

                return true;
            }


            return false;
        }

    }
}

customPage.html (located in the assets folded)

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript View</title>

    <script type="text/javascript">

        <!--JS -> Android-->
        function showToast() {
            window.location = "customschema://goto/";
        }

    </script>
</head>

<body>

</body>
</html>
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三岁会撩人
6楼-- · 2019-01-02 23:14

Same as Keith but shorter answer

webView.addJavascriptInterface(this, "android");
webView.loadUrl("javascript:android.onData(functionThatReturnsSomething)");

And implement the function

@JavascriptInterface
public void onData(String value) {
   //.. do something with the data
}

Don't forget to remove the onData from proguard list (if you have enabled proguard)

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祖国的老花朵
7楼-- · 2019-01-02 23:15

Here's what I came up with today. It's thread-safe, reasonably efficient, and allows for synchronous Javascript execution from Java for an Android WebView.

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 function(){})

First, add this to your Javascript file:

function evalJsForAndroid(evalJs_index, jsString) {
    var evalJs_result = "";
    try {
        evalJs_result = ""+eval(jsString);
    } catch (e) {
        console.log(e);
    }
    androidInterface.processReturnValue(evalJs_index, evalJs_result);
}

Then, add this to your Android activity:

private Handler handler = new Handler();
private final AtomicInteger evalJsIndex = new AtomicInteger(0);
private final Map<Integer, String> jsReturnValues = new HashMap<Integer, String>();
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 > waitMs)
            break;
        synchronized (jsReturnValueLock) {
            String value = jsReturnValues.remove(index);
            if (value != null)
                return value;

            long toWait = waitMs - (System.currentTimeMillis() - start);
            if (toWait > 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);
    }
}
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