Call Java function from JavaScript over Android WebView
I want to make a synchronous call to some Java code in my Android app.
I am using this solution: https://stackoverflow.com/a/3338656
My Java code:
final class MyWebChromeClient extends WebChromeClient {
public boolean onJsAlert(WebView view, String url, String message, JsResult result) {
Log.d("LogTag", message);
result.confirm();
return true;
}
}
My JavaScript code:
<html>
<script>
function java_request(){
alert('test');
}
</script>
<body>
<h2>Welcome</h2>
<div id="area"></div>
<form>
<input type="button" value="java_call" onclick="java_request()">
</form>
</body>
</html>
When I tap on the java_call button, the button goes to the pressed state. I can see 'test' in the console log. Everything is normal until here.
The problem is, the button never gets back to its normal state. It stays in the pressed state. Maybe the JavaScript execution is broken or something?
Why does the button never return to its normal state?
Answer
I don't think this is the best solution to get the javascript to execute java code. See here:
If you want to expose native code to the HTML to be callable via javascript, do the following around your web view declaration:
JavaScriptInterface jsInterface = new JavaScriptInterface(this);
webView.getSettings().setJavaScriptEnabled(true);
webView.addJavascriptInterface(jsInterface, "JSInterface");
Declare the class JavaScriptInterface:
public class JavaScriptInterface {
private Activity activity;
public JavaScriptInterface(Activity activity) {
this.activity = activity;
}
@JavascriptInterface
public void startVideo(String videoAddress){
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.parse(videoAddress), "video/3gpp");
activity.startActivity(intent);
}
}
I am declaring a single function for playing a video, but you can do whatever you want.
Finally you call this in the WebView contents via simple javascript call:
<video width="320" height="240" controls="controls" poster='poster.gif'
onclick="window.JSInterface.startVideo('file:///sdcard/test.3gp');" >
Your browser does not support the video tag.
</video>
The example is taken from another answer of mine, about playing videos, but should be explaining enough.
EDIT As per @CedricSoubrie's comment: if the target version of the application is set to 17 or higher you need to add annotation @JavascriptInterface above each method you want to export to the web view.