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Call JavaScript from C# object in Xamarin

I have been able to call JavaScript from C# inside the MainActivity but I'm trying to do so from an object. The majority of my app runs inside a WebView, my JavaScript calls to my C# Interface invoking an asynchronous function and when it's complete I would like to call back to my JavaScript but am unable to do so. Here is my current setup:
In my MainActivity I setup my WebView as such:
browser = FindViewById<WebView>(Resource.Id.mainView);
browser.SetInitialScale(1);
browser.SetWebChromeClient(new GeoWebChromeClient());
browser.Settings.UseWideViewPort = true;
browser.Settings.LoadWithOverviewMode = true;
if (Build.VERSION.SdkInt >= BuildVersionCodes.Kitkat)
{
WebView.SetWebContentsDebuggingEnabled(true);
}
browser.Settings.SetGeolocationEnabled(true);
browser.Settings.JavaScriptEnabled = true;
browser.AddJavascriptInterface(new JSCSMedium(this, ref browser), "Android");
browser.LoadUrl("file:///android_asset/web/index.html");
Then inside the JSCSMedium object I have an asynch function:
[Export]
[JavascriptInterface]
public void SyncApps()
{
Task t = Task.Run(() => {
IList<ApplicationInfo> tempApps = Application.Context.PackageManager.GetInstalledApplications(PackageInfoFlags.MatchDirectBootAware);
string packageName = "";
string appName = "";
for (int i = 0; i < tempApps.Count(); i++)
{
packageName = tempApps[i].PackageName;
appName = tempApps[i].LoadLabel(manager);
var root = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
var filePath = System.IO.Path.Combine(root, "system");
filePath = System.IO.Path.Combine(filePath, packageName);
if (!System.IO.Directory.Exists(filePath))
{
System.IO.Directory.CreateDirectory(filePath);
}
filePath = System.IO.Path.Combine(filePath, "icon.png");
if (!System.IO.File.Exists(filePath))
{
Drawable icon = tempApps[i].LoadIcon(Application.Context.PackageManager);
BitmapDrawable bd = (BitmapDrawable)icon;
CreateAppIcon(bd.Bitmap, packageName);
}
Intent intent = Application.Context.PackageManager.GetLaunchIntentForPackage(packageName);
if (intent != null)
{
apps.Add(tempApps[i]);
}
}
});
}
If I don't do the C# as an async function it runs and returns data fine, but this process takes a bit of time and blocks the app temporarily. Inside my MainActivity I can call JavaScript just fine with:
browser.EvaluateJavascript("javascript: alert('fooBar');", null);
But browser is not accessible inside the JSCSMedium. I've tried passing the browser object as a reference and normally but it throws an exception stating that the EvaluateJavascript function must be called on the same thread as where it was instantiated. I've also tried sending a reference of my MainActivity to the JSCSMedium and call a function inside the MainActivity to run the EvaluateJavascript but it seems to do nothing. No error, not crash, just nothing.

The problem is Task.Run forces the code to run in the thread pool, and browser.EvaluateJavascript needs to run on the main thread.
You have at least two options here, depending on your needs:
1) Run the EvaluateJavascript call inside the Task.Run block with something like:
var h = new Handler(Looper.MainLooper);
h.Post(() => browser.EvaluateJavascript("javascript: alert('fooBar');", null));
2) Run the EvaluateJavascript call outside the Task.Run block:
[Export]
[JavascriptInterface]
public async void SyncApps()
{
await Task.Run(() => {
//...
});
browser.EvaluateJavascript("javascript: alert('fooBar');", null);
}
Not really sure if you can change the return type of SyncApps(). If JS doesn't complain, you better change that too.

Spring #ExceptionHandler does not render view if webapp is restarted in the background

I'm dealing with a HttpSessionRequiredException and read about (https://spring.io/blog/2013/11/01/exception-handling-in-spring-mvc) how to catch it via the #ExceptionHandling annotation.
This does work since my breakpoint hits the spot. Unfortunately the string containing the view name does not trigger any view resolving and therefore no error page is being rendered.
Steps to Reproduce:
Open http://localhost:8080/manager (Session Attributes are being initialized)
Restart Web Application (Session/SessionAttributes are being reset)
Fill out form and press button (launches POST Request via AJAX - see Edit #2)
ExceptionHandler jumps in. Since a HttpSessionRequiredException is being thrown due the missing session attributes
Check Network Panel in Chrome which yields following information on the failed POST:
Controller Class incl. Exception Handler
#Controller
#Log
#RequestMapping(value = "/manager")
#SessionAttributes({"moduleDescriptors", "Environments", "moduleExecutionData"})
public class ManagerController {
private static final String MANAGER_VIEW = "manager";
private final ManagerHelper managerHelper;
private final ModuleExecution moduleExecution;
private final SystemProperties SystemProperties;
#Autowired
public ManagerController(ManagerHelper managerHelper, ModuleExecution moduleExecution,
SystemProperties SystemProperties) {
this.managerHelper = managerHelper;
this.moduleExecution = moduleExecution;
this.SystemProperties = SystemProperties;
}
#GetMapping
public ModelAndView render() {
ModelAndView modelAndView = new ModelAndView();
modelAndView.setViewName(MANAGER_VIEW);
modelAndView.addObject("moduleExecutionData", new ModuleExecutionData());
List<ModuleDescriptor> moduleDescriptorsFromServices = managerHelper.getModuleDescriptorsFromServices();
modelAndView.addObject("moduleDescriptors", moduleDescriptorsFromServices);
//TODO: Change varName for Systems
modelAndView.addObject("Environments", SystemProperties.getEnvironments());
log.info("Found " + moduleDescriptorsFromServices.size() + " module descriptors");
return modelAndView;
}
#PostMapping
public String execute(#ModelAttribute ModuleExecutionData moduleExecutionData) {
moduleExecution.execute(moduleExecutionData);
// sessionStatus.setComplete();
return MANAGER_VIEW;
}
#ExceptionHandler(HttpSessionRequiredException.class)
public String sessionError(){
return "sessionError";
}
}
My view lies within all the folder with all working views.
Any idea what I'm doing wrong? I'm configuring spring completely with annotations - not XML.
Edit:
I checked the response and saw that it actually returns the HTML of the View. But this HTML is not rendered. Is it because I made a POST request? Which actually ignores any return HTML?
But that does not make sense - because my original PostHandler does return a view as well and it is rendered.
PostHandler
#PostMapping
public String execute(#ModelAttribute ModuleExecutionData moduleExecutionData) {
moduleExecution.execute(moduleExecutionData);
return MANAGER_VIEW;
}
Edit #2
Here is the POST JavaScript Ajax logic
function postForm(event) {
const moduleId = $(event.currentTarget).data("module-id");
const formData = $("#" + moduleId).serialize();
$.ajax({
type: "post",
data: formData,
url: "/manager",
dataType: "json"
});
}

JXBrowser JSFunctionCallback and IFrame

I'm porting my jxbrowser integrations from 4.9x to 6.11.x, and i've got a problem with the JavaScript - JavaBridge with The IFrame. I register correctly with the follow code, and work as expect when I call the function from js in the main page. But doesn't work when the function is called from js inside the iframe.
browser.addScriptContextListener(new ScriptContextAdapter() {
#Override
public void onScriptContextCreated(ScriptContextEvent event) {
final Browser browser = event.getBrowser();
JSValue window = browser.executeJavaScriptAndReturnValue("window");
window.asObject().setProperty("resolveMsg", new JSFunctionCallback() {
#Override
public Object invoke(Object... params) {
String msgId = (String) params[0];
Builder builder = WrLocMsg.builder(msgId);
return builder.buildOriginalMessage();
}
});
}
});

Resolved by recovery window in this way:
JSValue window = browser.executeJavaScriptAndReturnValue(event.getJSContext().getFrameId(),"window");

Wicket AbstractDefaultAjaxBehavior do recursive update the page

I have some ajax Behaviour that should pick some data using JS, and turn it back to Java. Sometimes it works but quite ofen it is just add url parameter and do page refresing/
public abstract class LoggedVKIdBehaviour extends AbstractDefaultAjaxBehavior {
private static final Logger logger = LoggerFactory.getLogger(LoggedVKIdBehaviour.class);
#Override
protected void respond(AjaxRequestTarget target) {
String loggedVkId = RequestCycle.get().getRequest().getRequestParameters().getParameterValue("logged_vkid").toString();
logger.info("ajax has comming with logged VK ID " + loggedVkId);
recived(target, loggedVkId);
}
protected abstract void recived(AjaxRequestTarget target, String loggedVkId);
#Override
public void renderHead(final Component component, IHeaderResponse response) {
super.renderHead(component, response);
Map<String, Object> map = new HashMap<>();
map.put("callbackFunction", getCallbackFunction(CallbackParameter.explicit("logged_vkid")));
//
PackageTextTemplate ptt = new PackageTextTemplate(LoggedVKIdBehaviour.class, "vkid_callback.js");
OnDomReadyHeaderItem onDomReadyHeaderItem = OnDomReadyHeaderItem.forScript(ptt.asString(map));
response.render(onDomReadyHeaderItem);
}
}
js template
var calback = ${callbackFunction};
var logged_vk_id = 11;
function authInfo(response) {
if (response.session) {
logged_vk_id = response.session.mid;
calback(response.session.mid);
console.log("recived callback from VK " + logged_vk_id);
}
}
$(document).ready(function () {
VK.Auth.getLoginStatus(authInfo);
});
it is do recursive redirection like http://localhost:8080/mytool/product/1?logged_vkid=332797331&logged_vkid=332797331&logged_vkid=332797331&logged_vkid=332797331&logged_vkid=332773...
As i understand Ajaj technology - iti asynchronus requests, that shouldn't touch main url at all. So what is the reason for page refreshing?
this is generated Callback function
function (logged_vkid) {
var attrs = {"u":"../wicket/bookmarkable/com.tac.kulik.pages.product.ProductPage?12-1.IBehaviorListener.0-&productID=1"};
var params = [{"name":"logged_vkid","value":logged_vkid}];
attrs.ep = params.concat(attrs.ep || []);
Wicket.Ajax.ajax(attrs);
}
I use wicket 7.2

I did a lot investigations for few days. And found that when i remove
setPageManagerProvider(new NoSerializationPageManagerProvider(this));
Application throw me exepton in polite logs
org.apache.wicket.WicketRuntimeException: A problem occurred while
trying to collect debug information about not serializable object look
like it is could come from aused by: java.io.NotSerializableException:
com.tac.kulik.panel.smaccounts.SMAccountsPanel$1
which means that page tryed to be serialized for SOME REASON but $1 it is mean Anonimous class. I had few class created anonimously to ges some ajax links coming from ListView to be managed on parent panel. So After removing this Anonimous class logic, everything start and run well.
So i am happy, but still don't understand which reason page did serialization after ajax, and what the reason was to refresh whole page.

U2F JavaScript for Client Side in GWT (JSNI)

I'm trying to get response from U2F Token in GWT project using this source code:
public class Test implements EntryPoint {
#Override
public void onModuleLoad() {
Window.alert("Alert 3:"+u2FTest());
}
public static native String u2FTest()/*-{
var respond = {rep: "Clear"};
var RegistrationData = {"challenge":"dG7vN-E440ZnJaKQ7Ynq8AemLHziJfKrBpIBi5OET_0",
"appId":"https://localhost:8443",
"version":"U2F_V2"};
$wnd.u2f.register([RegistrationData], [],
function(data) {if(data.errorCode) {
alert("U2F failed with error: " + data.errorCode);
return;
}
respond.rep=JSON.stringify(data);
alert("Alert 1: "+respond.rep);
});
alert("Alert 2: "+respond.rep);
return respond.rep;
}-*/;
}
for some reasons I get The Alerts like so:
(Alert 2) first with "Clear" result
(Alert 3) with "Clear"
(Alert 1) with Token response
Normally I've to get (Alert 1) with Token response then 2,3. So how can I stop execution until I'll get the token response
Thank you,

Embrace asynchronicity!
public static native void u2FTest(com.google.gwt.core.client.Callback<String, Integer> callback) /*-{
// …
$wnd.u2f.register(regReqs, signReqs, $entry(function(response) {
if (response.errorCode) {
callback.#com.google.gwt.core.client.Callback::onFailure(*)(#java.lang.Integer::valueOf(I)(response.errorCode));
} else {
callback.#com.google.gwt.core.client.Callback::onSuccess(*)(JSON.stringify(response));
}
}));
}*-/;
(don't forget to wrap callbacks in $entry() so that exceptions are routed to the GWT.UnhandledExceptionHandler, if there's one)