如何在应用履历上的Android WebView中触发JavaScript事件

问题描述：

我的Android应用中有一个WebView，并且每当我需要运行JavaScript函数

I have a WebView in my Android app, and I need to run a JavaScript function whenever

已将应用程序/WebView切换到(例如，使用应用程序切换器或点击主屏幕上的图标)
设备从睡眠中唤醒(当设备进入睡眠状态时，应用仍在屏幕上)

使用 visibilitychange 我的网页javascript中的事件侦听器仅适用于情况1.

Using a visibilitychange event listener in my webpage javascript only works for case 1.

理想情况下，我想使用Android onResume() java函数触发某种javascript事件，但是如何?

Ideally I would like to trigger some kind of javascript event using the Android onResume() java function, but how?

答

您可以使用WebView

You can do this using the WebView evaluateJavascript() method.

首先，您需要在网页javascript中创建一个事件，并添加事件处理程序:

First of all you need to create an event in your webpage javascript, and add the event handler:

window.appResumeEvent = new Event('appresume');

window.addEventListener('appresume', yourFunction, false);

function yourFunction() {…}

设置在全局范围内创建应用恢复事件很重要(可以通过将其设置为 window 的属性来实现).

It's important that you set create the app resume event in global scope (which can be achieved by setting it as a property of the window).

现在，在您的Android onResume()方法中，运行 evaluateJavascript()方法:

Now, in your Android onResume() method, run the evaluateJavascript() method:

@Override
protected void onResume() {
    super.onResume();
    mainWebView.evaluateJavascript("(function() { window.dispatchEvent(appResumeEvent); })();", new ValueCallback<String>() {
        @Override
        public void onReceiveValue(String value) {

        }
    });
}

请注意，javascript必须包装在立即调用的函数表达式中.另请注意， dispatchEvent()将事件变量作为参数，而不是事件名称字符串.

Note the javascript has to be wrapped in an immediately-invoked function expression. Also note dispatchEvent() takes the event variable as the argument, not the event name string.

更多信息:在javascript中创建和调度事件(MDN)

对于我的完整 MainActivity.java ，请单击show snippet:

For my full MainActivity.java click show snippet:

import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends AppCompatActivity {

    private WebView mainWebView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mainWebView = findViewById(R.id.activity_main_webview);
        mainWebView.setWebViewClient(new WebViewClient());
        WebSettings webSettings = mainWebView.getSettings();
        webSettings.setJavaScriptEnabled(true);

        mainWebView.loadUrl("file:///android_asset/www/index.html");
    }

    @Override
    protected void onResume() {
        super.onResume();
        mainWebView.evaluateJavascript("(function() { window.dispatchEvent(appResumeEvent); })();", new ValueCallback<String>() {
            @Override
            public void onReceiveValue(String value) {

            }
        });
    }
}

如何在应用履历上的Android WebView中触发JavaScript事件

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