我尝试使用新的evaluateJavascript法Android 4.4系统，但所有我曾经得到的回复是一个空的结果：

I'm trying to use the new evaluateJavascript method in Android 4.4, but all I ever get back is a null result:

webView1.evaluateJavascript("return \"test\";", new ValueCallback<String>() {
    @Override
    public void onReceiveValue(String s) {
        Log.d("LogName", s); // Log is written, but s is always null
    }
});

我如何将结果返回给该方法？

How do I return a result to this method?

更新：多一点信息：

我在互联网权限集 我 setJavascriptEnabled（真）; 在尝试撇字符串：返回测试; ， 在试过JS对象：返回{测试：这个'} 的console.log（'测试'）; 正在执行细 设置 targetSdkVersion 19按： 如果您的应用程序使用的WebView 的 I have the INTERNET permission set I have setJavascriptEnabled(true); Tried apostrophe string: return 'test';, Tried JS object: return { test: 'this' } console.log('test'); is being executed fine. Set targetSdkVersion to 19 as per: If your app uses WebView

设备：两者的Nexus 7和Nexus 5（股票）

Devices: Both Nexus 7 and Nexus 5 (Stock)

推荐答案

目前正在此示例中使用的evaluateJavascript方法的一个例子：

There is an example of the evaluateJavascript method being used in this sample:

https://github.com/GoogleChrome/chromium-webview-samples/tree/master/jsinterface-example

从本质上讲，如果你在web视图执行JavaScript返回它会在回调传递一个值。

Essentially if the javascript you execute in the WebView returns a value it'll be passed in the callback.

主要的是要注意的是，在OnReceiveValue返回的字符串或者是一个JSON值，JSON对象，或JSON数组取决于你回什么。

The main thing to note is that the String returned in OnReceiveValue is either a JSON Value, JSON Object or JSON Array depending on what you return.

这里需要注意，这是如果返回一个值，你需要使用setLenient（真）在一个JSON读者为它工作。

Things to note about this is if you return a single value, you need to use setLenient(true) on a JSON reader for it to work.

     if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
        // In KitKat+ you should use the evaluateJavascript method
        mWebView.evaluateJavascript(javascript, new ValueCallback<String>() {
            @TargetApi(Build.VERSION_CODES.HONEYCOMB)
            @Override
            public void onReceiveValue(String s) {
                JsonReader reader = new JsonReader(new StringReader(s));

                // Must set lenient to parse single values
                reader.setLenient(true);

                try {
                    if(reader.peek() != JsonToken.NULL) {
                        if(reader.peek() == JsonToken.STRING) {
                            String msg = reader.nextString();
                            if(msg != null) {
                                Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG).show();
                            }
                        }
                    }
                } catch (IOException e) {
                    Log.e("TAG", "MainActivity: IOException", e);
                } finally {
                    try {
                        reader.close();
                    } catch (IOException e) {
                        // NOOP
                    }
                }
            }
        });
    }

您可能仍想使用一个解析器的字符串响应的原因是它被转换为一个JSON值，这意味着它将被包裹在引号。

The reason you may still want to use a parser for a string response is it is converted to a JSON value which means it will be wrapped in quotes.

例如，如果你去：

mWebView.evaluateJavascript("(function() { return 'this'; })();", new ValueCallback<String>() {
    @Override
    public void onReceiveValue(String s) {
        Log.d("LogName", s); // Prints: "this"
    }
});

这将打印字符串这一点，双引号括起来：这个

It would print the string this, wrapped in double quotes: "this".

其他值得注意的例子：

mWebView.evaluateJavascript("(function() { return null; })();", new ValueCallback<String>() {
    @Override
    public void onReceiveValue(String s) {
        Log.d("LogName", s); // Prints the string 'null' NOT Java null
    }
});

mWebView.evaluateJavascript("(function() { })();", new ValueCallback<String>() {
    @Override
    public void onReceiveValue(String s) {
        Log.d("LogName", s); //s is Java null
    }
});