How to listen for javascript events from a native android application?

Question

I have a native Android app that has a webView that loads a web page I have no control over.

In app I need to track/detect a “MessageEvent” that happens when a button is clicked on this page within the webView.

Scenario: User presses a button within the webView which fires off a "MessageEvent", When this “MessageEvent” is detected, a method in the Java/Kotlin code needs to be called, either through a listener that waits for this “MessageEvent” or another way(irrelevant how the method is called).

My main concern is how to detect this javascript “MessageEvent” event within my Java/Kotlin code.

score 1 · Accepted Answer · answered Jan 09 '23 at 11:34

I found the solution that seems to have worked, it was posted on another Answer:

Using our webview implementation. We implemented the onPageFinished method in order to inject our JS code to load the web:

override fun onPageFinished(url: String?) {
webview.loadUrl(
"javascript:(function() {" +
    "window.parent.addEventListener ('message', function(event) {" +
    " Android.receiveMessage(JSON.stringify(event.data));});" +
    "})()"
)
}

what we are doing is creating a listener that sends those messages to our own JS and Android Bridge interface. Which we've previously created in the webview setup in our Android activity as we normally do with addJavascriptInterface.

webview.addJavascriptInterface(JsObject(presenter), "Android”)

This way, we already have that communication bridge and all the messages sent by the postMessage will reach us in that interface that is subscribed with that listener.

class JsObject(val presenter: Presenter) {
    @JavascriptInterface
    fun receiveMessage(data: String): Boolean {
        presenter.onDataReceived(data)
        Log.d("Data from JS", data)
        return true
    }

Original Answer: https://stackoverflow.com/a/62500309/7849477

Hope it helps someone else.

score 0 · Answer 2 · answered Jan 06 '23 at 14:52

0

The answer here depends on why you want it ! One way to do it is with updating a field in database when the event is triggered and you need to have a looping check in your java code that asks the same database if the event was triggered ...
Also, You can't access that information directly ! Witch is very good to provide security for the user … imagine you take the user to his PayPal account and he sees a perfectly functioning PayPal web page with all purchases. If your android app has access to the scripts in his website, i think we all know what can happend.

answered Jan 06 '23 at 14:52

Yasser CHENIK

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This is a public event, which I can already see in the Chrome console after it is fired off, just like a click event, I just need a way to see the same event in the app. Example: after the event is emmited, I want to trigger a popup in app... From your first paragraph you are saying there is no way to do this from in App, only way is to have the original page update something externally and check it in App? – GNova Jan 06 '23 at 15:34
@GNova yes , exactly ! – Yasser CHENIK Jan 06 '23 at 16:13

How to listen for javascript events from a native android application?

2 Answers2