I have written a code in c#, javascript, using client library SignalR to refresh a page in database value change. My code is
<form asp-action="Start" method="post" class="form-stacked">
<button type="submit" id="startPractice" class="button-primary">Start Practice</button>
</form>
<script src="~/js/ignalr/dist/browser/signalr.js"></script>
<script src="~/js/chat.js"></script>
My API method is which is called while clicking start practice is
public async Task<IActionResult> Index(long sessionId)
{
// Database change logic
SignalRClientHub sr = new SignalRClientHub();
await sr.SendMessage();
// Rest of the logic
return this.View();
}
public class SignalRClientHub : Hub
{
public async Task SendMessage(string user = null, string message = null)
{
await Clients.All.SendAsync("ReceiveMessage", user, message);
}
}
code of chat.js
"use strict";
var connection = new signalR.HubConnectionBuilder().withUrl("/SignalRClient").build();
connection.on("ReceiveMessage", function (user, message) {
location.reload();
});
When I click the button start practice it hits SendMessage Method, but I got an error
object reference not set to an instance
because the value of the Client was null. How Can I fix this?
You cannot new up a hub manually. In order to send to clients from outside of the hub you need to use the IHubContext<THub>. See the docs for details https://learn.microsoft.com/aspnet/core/signalr/hubcontext?view=aspnetcore-5.0
Related
I'm making an Android app using webview.
The app can print out receipts. What I want to do is when the printer is not working, alert box shows up to tell the printer isn't working, and return false to the form's onsubmit event to prevent form from being submitted.
Java code:
public class JSKicker {
#JavascriptInterface
public void callPrint(final String argumet) {
Thread thread = new Thread(new Runnable() {
public void run() {
int nRtn;
connectionNum = myPrinter.Connect("000.000.0.000");
if(connectionNum < 0){ //Printer not working
webview.post(new Runnable() {
#Override
public void run() {
String script = "alert('Printer Error'); return printer_connection = false;";
webview.evaluateJavascript(script, new ValueCallback<String>() {
#Override
// I can't figure out what to do here...
});
}
});
}else{ //Printer is working properly
connectionNum = myPrinter.SetLocale(8);
strText = argument;
nRtn = myPrinter.PrintText(strText, "SJIS");
nRtn = myPrinter.PaperFeed(64);
nRtn = myPrinter.CutPaper(1);
myPrinter.Disconnect();
}
}
});
thread.start();
}
JavaScript in header:
<script type="text/javascript">
function gate(){
jQuery.ajax({
url:'/cart_info.php',
type:'GET'
})
.done( (data) => {
window.JSKicker.callPrint(data);
})
if (printer_connection = false) {
return false;
}else{
return true;
}
}
</script>
HTML form tag:
<form method="post" id="order_form" onsubmit="return gate();">
How can I get this work?
Could you do it thru WebView.evaluateJavascript()?
https://developer.android.com/reference/android/webkit/WebView.html#evaluateJavascript(java.lang.String,%20android.webkit.ValueCallback%3Cjava.lang.String%3E)
So with that you could send simple CustomEvent to document in WebView
webView.evaluateJavascript("document.dispatchEvent(new Event('printer_error', { details: "No printer found!" }));");
and in JavaScript you can hook listener for your custom event to react.
document.addEventListener('printer_error', e => alert(e.details));
Didn't test this so might be that at least evaluateJavascript() needs callback function.
WebSocket can solve your problem.
WebSockets provide a persistent connection between a client and server that both parties can use to start sending data at any time. The client establishes a WebSocket connection through a process known as the WebSocket handshake.
Its very straight forward and easy to implement.
You can follow referrer links for more details:-
JAVA WebSocket:- WebSocket using Spring Boot, WebSocket using Simple JEE
Browser WebSocket(JavaScript):- WebSocket API
In Android ,if you want webview pass value to JavaScript.
First,you need to set the webview enable the JavaScript,
private WebView mWebView;
void onCreate(){
mWebView = findViewById(R.id.webview);
WebSettings webSettings = mWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
webSettings.setSupportZoom(false);
}
And ,in you want do some thing code
if(connectionNum < 0){ //Printer not working
// I need to do something here to send a message that the printer isn't working to JS.
//In thread can not use mWebView,should send message to MainThread to do
// mWebView.loadUrl("javascript:javaCall()");
Message msg = new Message();
msg.what = 1;
myHandler.sendMessage(msg);
//myHandler can be your MainThread send to here
}
And where the mWebView created in your code, be in main thread ,you can use the
Handler to deal with the message sended to here.
private Handler myHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
// this 1 is just thread send to here
if (msg.what == 1) {
//and here can do the webview UI method
mWebView.loadUrl("javascript:javaCall()");
}
}
};
the javaCall() is where you JacaScript invoke method,in javaScript you can writre like this:
<script language="javascript">
function javaCall(){
alert("Printer Error");
//other thing you can do
}
</script>
if you have problem ,you can refer to the official document.
public void loadUrl (String url)
Loads the given URL.
Also see compatibility note on evaluateJavascript(String, ValueCallback).
webview use link
To put it simply, I need a way for client side code to be able to trigger a server side method in my project. The way that I'm trying to use such functionality is when a user inputs their email address into a textbox, after each character is typed I want the project to trigger the method shown below which uses a class to query my database.
private void EmailCheck()
{
lblEmailError.Text = null;
Customer y = new Customer();
int counter = 0;
y.Email = Email.Text;
counter = y.CheckEmail();
if (counter.Equals(1))
{
lblEmailError.Text = "Email is already in use";
}
else
{
lblEmailError.Text = null;
}
}
I currently have almost no experience of any kind with JavaScript or any form of client side scripting. As I understand, AJAX may be of use to me here but again I am clueless about how I would implement it. I've also heard about onkeydown/press/up but again I am not sure how to alter online solutions to my specific need. Any help?
The most straightforward way would be to make a button in HTML5, use jQuery $.ajax() function to invoke a server side REST API (implementation could be anything C# Web API, Python Flask API, Node.JS API).
In your client side:
<label> Enter something into the textbox </label>
<input type = "text" id = "myTextBox" placeholder="Enter something"/>
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.2.1.min.js"></script>
<script>
$(function(){
//On button click query the server
$("#myTextBox").change(function(){
var textBoxValue = $("#myTextBox).val();
var dataToBeSent = {
"data": textBoxValue
};
$.ajax(function(){
url: "http://localhost:9999/api/YourAPIName",
method: "POST",
data: JSON.stringify(dataToBeSent),
success: function(data){
console.log(data);
},
error: function(jqXHR, textStatus, errorThrown){
console.log("Failed because" + errorThrown);
}
}); //end .ajax
}); //end click
}); //end jQuery
</script>
In your Server side (Assuming C#):
Make a model class, with properties the same name as the JSON key you constructed for the [FromBody] attribute to deserialize it correctly.
public class SomeModelClass
{
public string data { get; set; }
}
[HttpPost]
[Route("api/YourAPIName")]
public HttpResponseMessage YourMethod([FromBody] SomeModelClass modelClass)
{
//perform logic and return a HTTP response
}
In the View I have a linked button and there is java scripts to collect information from view and then post to the corresponding action 'GroupDeny'
#Html.ActionLink("Deny Selected", "GroupDeny", null, new { #class = "denySelectedLink" })
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
<script type="text/javascript">
$(document).on('click', '.denySelectedLink', function (e) {
//Cancel original submission
e.preventDefault();
var identifiers = new Array();
//build the identifiers . . .
var jsonArg = JSON.stringify(identifiers);
$.post('/LicenseAssignment/GroupDeny?licensePermissionIdentifiers=' + encodeURIComponent(jsonArg));
});
</script>
Then in the controller, the GroupDeny will update the DB and then
call RedirecToAction in order to refresh the view
public class LicenseAssignmentController : Controller
{
[HttpPost]
public ActionResult GroupDeny(string licensePermissionIdentifiers)
{
// changes the DB
return RedirectToAction("Index");
}
// GET:
public async Task<ActionResult> Index()
{
var model = get data from DB
return View(model);
}
Everything seems work as expected, The Index will be called after the RedirectToAction("Index") is executed, and the model is update to date their when I watch it during debugging, the only problem is that the page is not refreshed at all, that is to say the view still keep unchanged, but after I refresh the page manually (press F5), the data will be updated with the values from DB
We use AJAX when we don't want to navigate away from the page. Your $.post() is an AJAX request.
Since you want navigation add a form to your page
#using(Html.BeginForm("GroupDeny", "LicenseAssignment", FormMethod.Post))
{
<input type="hidden" value=""
name="licensePermissionIdentifiers"
id="licensePermissionIdentifiers" />
}
Now submitting this form will navigate
$(document).on('click', '.denySelectedLink', function (e) {
e.preventDefault(); // prevent link navigation
var identifiers = new Array();
//build the identifiers . .
// populate the form values
$("#licensePermissionIdentifiers").val(identifiers);
$("form").submit();
});
The RedirectToAction() returns to the browser a 302 Redirect to LicenseAssignment/Index then you hit the Index action.
Since you are using Ajax you will have to redirect on the return of your $.post call and change your GroupDeny to a JsonResult.
Something like this maybe:
JS
$.post('/LicenseAssignment/GroupDeny?licensePermissionIdentifiers=' + encodeURIComponent(jsonArg), function(data){
if(data.Success){
//redirect
window.location.reload();
}else{
//handle error
}
});
Controller Action
[HttpPost]
public JsonResult GroupDeny(string licensePermissionIdentifiers)
{
// changes the DB
return Json(new { Success = true });
}
I have the following action in ASP.NET MVC4
public ActionResult Register(RegisterModel model)
{
if (ModelState.IsValid)
{
// Attempt to register the user
try
{
WebSecurity.CreateUserAndAccount(model.UserName, model.Password);
WebSecurity.Login(model.UserName, model.Password);
// ?? Need some code here
}
catch (MembershipCreateUserException e)
{
ModelState.AddModelError("", ErrorCodeToString(e.StatusCode));
}
}
// If we got this far, something failed, redisplay form
return View(model);
}
I have the following code that calls this:
$('#article').on('submit', '#loginForm, #registerForm', function (e) {
e.preventDefault();
var $form = $(this);
var href= $form.attr('data-href');
$form.validate();
if (!$form.valid()) {
return false;
}
var data = $form.serializeArray();
$.ajax(
{
data: data,
type: 'POST',
url: href
})
.done(submitDone)
.fail(submitFail);
function submitDone(content) {
$('#article').html(content)
}
function submitFail() {
alert("Failed");
}
return false;
});
If the registration works I would like to force the whole web page to refresh. Is there
a way that I can send back a message from the actionmethod to the javascript to
tell it that the registration works and the javascript should refresh the whole
web page?
I did try return RedirectToLocal("/"); but this definitely does not work. What
this does is to return a new page and then have it populated in the #article DIV.
There is nothing that will automatically refresh the browser from the server.
To refresh the browser from the server you'll need to send something from the server to the client indicating that you want to refresh the page. You'll need to write the javascript to look for the indication to refresh the browser.
Client Code
function submitDone(content) {
var json = $.parseJson(content);
if(json.isSuccess) {
//Do something here
}
$('#article').html(json.content)
}
Server code
public ActionResult Register(RegisterModel model)
{
if (ModelState.IsValid)
{
// Attempt to register the user
try
{
WebSecurity.CreateUserAndAccount(model.UserName, model.Password);
WebSecurity.Login(model.UserName, model.Password);
// ?? Need some code here
}
catch (MembershipCreateUserException e)
{
ModelState.AddModelError("", ErrorCodeToString(e.StatusCode));
}
}
// If we got this far, something failed, redisplay form
return Json(new {isSuccess = true, content = model});
}
I am unsure of what you are trying to accomplish by refreshing the page, if it's to clear out the form fields. The same could be achieved by using JavaScript. By using javascript instead of a page refresh you won't lose page state, such as error messages.
well i can think of a quick javascript trick to refresh a page on success like this
function submitDone(content) {
window.location.reload();
}
this will reload the page on the success.
In my project I need to add functionality, that show infobox in right top corner of page, when client save something. Everything works fine when save operation do redirect to another page in my solution.
Client run save action:
[SaveAction] //my own action filter to show info box
public ActionResult Details(int id, FormCollection form)
{
var pojazd = PojazdRepo.GetById(id);;
if (UpdateAndSave(pojazd, form))
{
return RedirectToAction("Index");
}
else
{
return View(GetDetailsViewModel(id, true));
}
}
Now my action filter test that ModelState.IsValid is true then add something to TempData:
public class SaveActionAttribute : ActionFilterAttribute
{
private bool test;
private bool isAjax;
public override void OnActionExecuted(ActionExecutedContext ctx)
{
test = ctx.Controller.ViewData.ModelState.IsValid;
isAjax = ctx.HttpContext.Request.IsAjaxRequest();
base.OnActionExecuted(ctx);
}
public override void OnResultExecuting(ResultExecutingContext ctx)
{
if (test)
{
if (isAjax) ctx.Controller.TempData["ActionPopUp"] = "";
else ctx.Controller.TempData["ActionPopUp"] = "save";
}
base.OnResultExecuting(ctx);
}
}
And my Site.Master run script if TempData["ActionPopUp"] = "save":
<script type="text/javascript">
$(document).ready(function () {
var test = '<%: TempData["ActionPopUp"] %>';
if (test != '') SaveSuccessPopUp(test);
});
</script>
As mentioned, this solution works fine, when controller make Redirect and Site.Master is loaded again, my problem is, how to inject SaveSuccessPopUp() function to action result, when Action was called by AJAX and return something, what don't reload page and don't run Site.Master $(document).ready code block.
Nice question.
You need to probably work with partial view here. I mean if your request is an ajax request, append the TempData again and the TempData will be outputted inside the partial view.
How will you send that partial view output as chunk of html?
I have a blog post about how you can send the partial view as string. The topic is different but you will get the idea:
http://www.tugberkugurlu.com/archive/working-with-jquery-ajax-api-on-asp-net-mvc-3-0-power-of-json-jquery-and-asp-net-mvc-partial-views
Here is an example:
[HttpPost]
public ActionResult toogleIsDone(int itemId) {
//Getting the item according to itemId param
var model = _entities.ToDoTBs.FirstOrDefault(x => x.ToDoItemID == itemId);
//toggling the IsDone property
model.IsDone = !model.IsDone;
//Making the change on the db and saving
ObjectStateEntry osmEntry = _entities.ObjectStateManager.GetObjectStateEntry(model);
osmEntry.ChangeState(EntityState.Modified);
_entities.SaveChanges();
var updatedModel = _entities.ToDoTBs;
//returning the new template as json result
return Json(new { data = this.RenderPartialViewToString("_ToDoDBListPartial", updatedModel) });
}
RenderPartialViewToString is a controller extension. you can find the the complete code for that from below link:
https://bitbucket.org/tugberk/tugberkug.mvc/src/6cc3d3d64721/TugberkUg.MVC/Helpers/ControllerExtensions.cs
After you have your html back on the client side code, append it you DOM and work on it. Animate it, show/hide it, do whatever you need with it