WebView JS交互 addJavascriptInterface

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目录

目录

• 目录
• WebView JS交互 addJavascriptInterface
  • addJavascriptInterface
  • removeJavascriptInterface
  • evaluateJavascript
  • 案例
    • 原生代码
    • 前端代码

WebView JS交互 addJavascriptInterface

Demo

注意，如果在 java 与 Javascript 交互的时候出现如下错误：

Uncaught ReferenceError: <pre name="code" class="html">getDeviceID 

很可能是因为在 html 页面还没有加载完，就加载里面的 JS 方法，这样是找不到这个方法的。

解决方法为：把调用放到 onPageFinished() 里面。

addJavascriptInterface

addJavascriptInterface

void addJavascriptInterface(Object object, String name)

参数：

• Object object : the Java object to inject注入 into this WebView's JavaScript context. Null values are ignored.
• String name : the name used to expose暴露、公开 the object in JavaScript

方法说明：

• Injects the supplied Java object into this WebView.
• The object is injected into the JavaScript context of the main frame, using the supplied name.
• This allows the Java object's methods to be accessed from JavaScript.
• For applications targeted to API level JELLY_BEAN_MR1 and above, only public methods that are annotated with JavascriptInterface can be accessed from JavaScript.
• For applications targeted to API level JELLY_BEAN or below, all public methods (including the inherited继承的 ones) can be accessed, see the important security note安全注意事项 below for implications意义、含义.
• Note that injected objects will not appear in JavaScript until the page is next (re)loaded. JavaScript should be enabled before injecting the object.

使用案例：

class JsObject {
    @JavascriptInterface
    public String toString() { return "injectedObject"; }
}

webview.getSettings().setJavaScriptEnabled(true);
webView.addJavascriptInterface(new JsObject(), "injectedObject");
webView.loadData("", "text/html", null);
webView.loadUrl("javascript:alert(injectedObject.toString())");

IMPORTANT

• This method can be used to allow JavaScript to control the host application.
• This is a powerful feature, but also presents a security risk for apps targeting JELLY_BEAN or earlier.
• Apps that target a version later than JELLY_BEAN are still vulnerable很容易受到攻击 if the app runs on a device running Android earlier than 4.2.
• The most secure way to use this method is to target JELLY_BEAN_MR1 and to ensure the method is called only when running on Android 4.2 or later.
• With these older versions, JavaScript could use reflection to access an injected object's public fields.
• Use of this method in a WebView containing untrusted content could allow an attacker攻击者 to manipulate操纵 the host application in unintended非预期 ways, executing执行 Java code with the permissions of the host application.
• Use extreme care格外小心 when using this method in a WebView which could contain untrusted content.

说明：

• JavaScript interacts with交互 Java object on a private, background thread of this WebView. Care is therefore required to maintain保持 thread safety.
• The Java object's fields are not accessible.
• For applications targeted to API level LOLLIPOP and above, methods of injected Java objects are enumerable枚举 from JavaScript.

removeJavascriptInterface

void removeJavascriptInterface(String name)

String name : the name used to expose暴露 the object in JavaScript. This value must never be null.

Removes a previously injected Java object from this WebView.
Note that the removal will not be reflected in JavaScript until the page is next (re)loaded.

evaluateJavascript

void evaluateJavascript (String script, ValueCallback<String> resultCallback)

参数：

String script : the JavaScript to execute.

ValueCallback resultCallback :

• A callback to be invoked when the script execution completes with the result of the execution (if any).
  当脚本执行完成时的回调，如果有执行结果的话会携带执行结果。
• May be null if no notification of the result is required.
  如果不需要结果通知，可以为null。

说明：

• Asynchronously evaluates JavaScript in the context of the currently displayed page.
  在当前显示页面的上下文中异步执行JavaScript。
• If non-null, resultCallback will be invoked with any result returned from that execution.
  如果非空，resultCallback会被回调并携带调用后返回的结果。
• This method must be called on the UI thread and the callback will be made on the UI thread.
  此方法必须在UI线程上调用，并且回调也是运行在UI线程上的。

Compatibility note 兼容性说明

• Applications targeting N or later, JavaScript state from an empty WebView is no longer persisted across navigations like loadUrl(String).
  目标版本为N或更高的应用程序，空的WebView中的JavaScript状态不再继续像loadUrl那样在navigations中保留。
• For example, global variables and functions defined before calling loadUrl(String) will not exist in the loaded page.
  例如，在调用loadUrl之前定义的全局变量和函数将不会存在于加载的页面中。
• Applications should use addJavascriptInterface(Object, String) instead to persist JavaScript objects across navigations.
  应用程序应该使用 addJavascriptInterface 来跨navigations维护(持久化)JavaScript对象。

案例

原生代码

webview.addJavascriptInterface(new JSInterface(this, webview), JSInterface.JS_INTERFACE_NAME);

public class JSInterface {
    public static final String JS_INTERFACE_NAME = "JSInterface";//JS调用类名
    private Context mContext;
    private WebView webView;
    
    public JSInterface(Context context, WebView webView) {
        this.mContext = context;
        this.webView = webView;
    }
    
    @JavascriptInterface
    public void hello(String content) {
        Log.i("bqt", "JS 调用原生时是否发生在主线程：" + (Looper.myLooper() == Looper.getMainLooper()));//false
        new Handler(Looper.getMainLooper()).post(() -> //WebView等UI操作必须在主线程中进行
                Toast.makeText(mContext, "原生的hello方法被调用了：" + content, Toast.LENGTH_SHORT).show());
        
        SystemClock.sleep(3000);//模拟耗时操作
        
        String call = "javascript:javacalljs(" + System.currentTimeMillis() + ")";//格式很重要，大部分错误都是由于格式问题导致的
        new Handler(Looper.getMainLooper()).post(() -> webView.loadUrl(call));//WebView等UI操作必须在主线程中进行
    }
    
    @JavascriptInterface
    public void hello2(String content) {
        new Handler(Looper.getMainLooper()).post(() -> Toast.makeText(mContext, content, Toast.LENGTH_SHORT).show());
        
        SystemClock.sleep(3000);//模拟耗时操作
        
        String call = "javascript:javacalljs2(" + System.currentTimeMillis() + ")";//JS此方法的返回值会通过onReceiveValue回调到原生
        new Handler(Looper.getMainLooper()).post(() -> webView.evaluateJavascript(call, value -> {
            Log.i("bqt", "ValueCallback 是否发生在主线程：" + (Looper.myLooper() == Looper.getMainLooper()));//true
            Toast.makeText(mContext, "【onReceiveValue】" + value, Toast.LENGTH_SHORT).show();
        }));
    }
}

前端代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<button onclick='jscalljava("包青天")'>点击后调用 JS 的 jscalljava 方法，在此方法中 JS 调用原生 JSInterface 类中的 hello 方法，原生 hello 方法执行完操作后回调 JS 中的 javacalljs 方法</button>
<button onclick='jscalljava2()'>演示原生调用 JS 方法后，JS 将执行完return的结果通过原生提供的 ValueCallback 对象的 onReceiveValue 方法回调给原生</button>

</body>

<script type="text/javascript">
function jscalljava(content){
    console.log("【jscalljava】");
    JSInterface.hello(content);
}

function jscalljava2(){
    console.log("【jscalljava2】");
    var content="[\"包青天\",\"白乾涛\",\"bqt\"]";
    JSInterface.hello2(content);
}

function javacalljs(content){
    console.log("【js中的javacalljs方法被调用了】content="+content);
}

function javacalljs2(content){
    console.log("【js中的javacalljs2方法被调用了】content="+content);
    return 20094;
}

</script>
</html>

2018-04-15