There is an Android mechanism that alows you to run Android function from javascript:
<input class="button" type="button" value="FREE life" onclick="startRewardVideo('some parameters can be passed to Android from here')">
<script type="text/javascript">
function startRewardVideo(paramFromJS) {
Android.startRewardVideoAndroidFunction(paramFromJS);
}
</script>
now you need class that knows what to do with your javascript:
public class MyJavaScriptInterface {
@JavascriptInterface // this annotation is importatn
public void startRewardVideoAndroidFunction(String paramFromJS) {
//here you need to start showing reward movie
//because this function will be called after webView button click.
}
}
last step is to connect webView with your javascript interface:
webView.addJavascriptInterface(new MyJavaScriptInterface(), "Android");
and of course don't forget to enable javascript for your webView:
webView.getSettings().setJavaScriptEnabled(true);
Hope it helps :) Ask if you have any questions on this.
Here you have full tutorial