I am creating an application in Silverlight 4. The first screen the user comes in contact with is the Login screen (Login.xaml). I have written the following code in Login.xaml.cs file.
private void btnSubmit_Click(object sender, RoutedEventArgs e)
{
//first validate if the user is authorised for this application
if (this.ValidateEntry())
{
if (UserAuthenticationBL.AuthenticateUser(txtUserName.Text.Trim(), txtPassword.Password.Trim()))
{
//since the user is authenticated we will show the dashboard screen
this.Content = new MainPage();
}
else
{
this.ShowErrorMessage("Invalid username or password");
txtUserName.Focus();
}
}
}
My problem is that the code gets executed before i get the data in the AuthenticateUser method. The code immediately comes down to the "Invalid username or password" and the list is loaded after all the execution on the xaml page has finished.
I know there is something going wrong with the Asynchronous thingi...and i also know i need to put an event to know when the loading has completed........
but i dont know how to go about it!!!
can someone please put some light on this issue...
thank you.
If I understood it right, your AuthenticateUser method is running async, right?
You have to define a callback to the AuthenticateUserComplete event and run the method in the button submit event. In the callback write this if/else clause, then it will be called once the asynchronous method was completed.
Just one question, why are you doing asynchronously if your behavior should be synchronous? (You have to get the answer before deciding what to do).
This http://msdn.microsoft.com/en-us/library/aa719598%28VS.71%29.aspx
may be helpful :)
Oscar
Related
I am very new to both java and vaadin. Hope to be able to get some good tips on how I can improve my code.
I would like to rewrite the code below to use Vaadin´s -> LoginOverlay instead of the code below.
As I said, I'm trying to learn so I have used the code for this example: https://www.youtube.com/watch?v=oMKks5AjaSQ&t=1158s
However, LoginOverlay seems to be a better way to display its login part through. As in this example: https://www.youtube.com/watch?v=pteip-kZm4M
So my question is how can you write the code below as a LoginOverlay.
public class LoginView extends Div {
public LoginView(AuthService authService) {
setId("login-view");
var username = new TextField("Username");
var password = new PasswordField("Password");
add(
new H1("Welcome"),
username,
password,
new Button("Login", event -> {
try {
authService.authenticate(username.getValue(), password.getValue());
UI.getCurrent().navigate("home");
} catch (AuthService.AuthException e) {
Notification.show("Wrong credentials.");
}
}),
new RouterLink("Register", RegisterView.class)
);
}
}
I have only come this far to convert the code.
A clarification of the new part of the code. The code does not work. The part with loginOverlay.addLoginListener (event -> probably needs to be written in a different way.
I'm using IntelliJ 2020.3.4 if that is of any help.
public class LoginView2 extends Composite<LoginOverlay> {
public LoginView2(AuthService authService) {
setId("login-view");
LoginOverlay loginOverlay = getContent();
loginOverlay.setTitle("Welcom");
loginOverlay.setDescription("Manage your business tasks");
loginOverlay.setOpened(true);
loginOverlay.addLoginListener(event -> {try {
if(authService.authenticate(username.getValue(), password.getValue());
UI.getCurrent().navigate("home");
} catch (AuthService.AuthException e) {
Notification.show("Wrong credentials.");
}
}),
new RouterLink("Register", RegisterView.class);
}
}
}
}
Super grateful for all the help you can give.
Many thanks to everyone who makes stackoverflow so amazing.
Copy-pasting code snippets with little idea about what the code does is a recipe for disaster, especially when it comes to security.
You have all kinds of errors in your code: misplaced braces, using variables that do not exist, and a RouterLink far from where it belongs.
I understand you've got to start somewhere. I would recommend starting from code that actually compiles, and then gradually adding things, testing what you have so far at every step.
Here are some tips for your LoginView2:
Remove the whole loginOverlay.addLoginListener(...) code, including the authService.authenticate call and the RouterLink. Make sure that you can run the application at this point, and that you can see the login overlay.
Add back the login listener, but for now just show a notification in it. Test that you can run the application, and that if you click Login, your notification is displayed.
loginOverlay.addLoginListener(event -> {
Notification.show("This is working");
});
Implement the authentication. You have a call to authService.authenticate(...) inside an if-statement, but the method does not return anything. Instead, it throws an exception if the authentication fails, hence the try-catch. This means that inside the try { ... } block, any code you put after the authService.authenticate(...) call is only executed if it did not throw an exception, i.e. if the authentication was successful.
There are no username or password variables. The first YouTube video had defined these variables in the form of text fields. With the login overlay, it creates those fields for you, so how do you get the corresponding values from it?
I'm using MVC 4 and I have the following code :
public void DoWork(string connectionId)
{
connectionId = this.connectionId;
var a = MakeADelayAsync();
}
public async Task MakeADelayAsync()
{
await Task.Delay(5000);
var generalHubContext = GlobalHost.ConnectionManager.GetHubContext<GeneralHub>();
generalHubContext.Clients.Client(connectionId).showNotification("Completed");
}
"DoWork" method is my mvc action. what I intent to do is when the action button is pressed the "DoWork" calls an async method and returns to the client immediately. when the async method has completed his job it will notify client using signalR.
The problem is in the "MakeADelayAsync" method, those two lines after await won't be called ever. It seems that the flow never continues after await.
First question is Where is the problem in "MakeADelayAsync" ?
Second question is why do I have to write a useless code of var a = MakeADelayAsync(); to avoid compiler warning while I'm completely aware of what I am doing? I never use "a" anyway.
"DoWork" method is my mvc action. what I intent to do is when the action button is pressed the "DoWork" calls an async method and returns to the client immediately. when the async method has completed his job it will notify client using signalR.
Doing this is extremely dangerous. I strongly recommend that you use a persistent queue, as I said in my previous answer: Azure queue, MSMQ, WebSphere MQ, etc.
However, if you insist on doing it the dangerous way, then you can use the code that I have on my blog to execute background work on ASP.NET outside of a request context:
public void DoWork(string connectionId)
{
connectionId = this.connectionId;
// This is extremely dangerous code! If ASP.NET unloads
// your app, then MakeADelayAsync may not run to completion.
BackgroundTaskManager.Run(() => MakeADelayAsync());
}
First question is Where is the problem in "MakeADelayAsync" ?
You're executing code that is attempting to resume on the request context after the request is completed and the request context is disposed. It's the same problem you had before.
Second question is why do I have to write a useless code of var a = MakeADelayAsync(); to avoid compiler warning while I'm completely aware of what I am doing?
The compiler warning is telling you that the code is almost certainly a mistake... and the compiler is right.
can you try to mark your DoWork method as async?
public async void DoWork(string connectionId)
{
connectionId = this.connectionId;
var a = MakeADelayAsync();
}
I have a safari extension popover that needs to communicate with its global page. From a content-script I am using
safari.self.tab.dispatchMessage(name,data);
to accomplish that. From a popover I didn't find a way to do that. I know that I can access methods in the global page directly
safari.extension.globalPage.contentWindow
but my goal was to reuse code fragments that are already used in content-scripts. I do the same for the chrome version of the plugin.
Is there code for a little clever proxy that emulates
safari.self.tab.dispatchMessage(name,data);
from the popover?
To be honest it's probably just easier to have different code in your popover and injected scripts. If you really want, you could do something like this:
function dispatchMessage(name, message) {
if (safari.self.tab) {
safari.self.tab.dispatchMessage(name, message);
} else if (safari.extension.globalPage.contentWindow) {
safari.extension.globalPage.contentWindow.handleMessage({name: name, message: message});
}
}
Then just use dispatchMessage('foo', 'bar') in both your popover and injected scripts. It's a bit hacky though, because the message event object normally has more information on it than just the name and message, and you have to ensure that your handleMessage function is actually the same function that is assigned as the message event listener in the global page.
A simplistic way to accomplish reusing your message-based content script code in your popover is by wrapping the safari.self.tab.dispatchMessage calls in an abstraction function that I'll describe below...
But first, you need to make sure to have a single named handler function in your global page that handles all messages, like this:
function handleMessage(evt) {
switch (evt.name) {
case 'Message1':
// do something with evt.message
break;
case 'Message2':
// do something else with evt.message
break;
}
}
safari.application.addEventListener('message', handleMessage, false);
If you have separate handlers for each different message, or if you're using an anonymous function, this approach will not work.
Now, the wrapper function that goes in your popover and content scripts is very simple:
function tellGlobalPage(msgName, msgData) {
if (safari.self instanceof SafariExtensionPopover) {
// this script is running in a popover
var fakeMsgEvt = { name: msgName, message: msgData };
safari.extension.globalPage.contentWindow.handleMessage(fakeMsgEvt);
} else {
// this script is a content script
safari.self.tab.dispatchMessage(msgName, msgData);
}
}
And then instead of safari.self.tab.dispatchMessage(name, data), you use tellGlobalPage(name, data).
Please note that this simplistic approach doesn't deal with roundtrip messaging, where the popover or content script sends a message to the global page, and the global page replies with another message. There are other approaches that can handle that.
The problem: I'm crashing when I want to render my incoming data which was retrieved asynchronously.
The app starts and displays some dialog boxes using XAML. Once the user fills in their data and clicks the login button, the XAML class has in instance of a worker class that does the HTTP stuff for me (asynchronously using IXMLHTTPRequest2). When the app has successfully logged in to the web server, my .then() block fires and I make a callback to my main xaml class to do some rendering of the assets.
I am always getting crashes in the delegate though (the main XAML class), which leads me to believe that I cannot use this approach (pure virtual class and callbacks) to update my UI. I think I am inadvertently trying to do something illegal from an incorrect thread which is a byproduct of the async calls.
Is there a better or different way that I should be notifying the main XAML class that it is time for it to update it's UI? I am coming from an iOS world where I could use NotificationCenter.
Now, I saw that Microsoft has it's own Delegate type of thing here: http://msdn.microsoft.com/en-us/library/windows/apps/hh755798.aspx
Do you think that if I used this approach instead of my own callbacks that it would no longer crash?
Let me know if you need more clarification or what not.
Here is the jist of the code:
public interface class ISmileServiceEvents
{
public: // required methods
virtual void UpdateUI(bool isValid) abstract;
};
// In main XAML.cpp which inherits from an ISmileServiceEvents
void buttonClick(...){
_myUser->LoginAndGetAssets(txtEmail->Text, txtPass->Password);
}
void UpdateUI(String^ data) // implements ISmileServiceEvents
{
// This is where I would render my assets if I could.
// Cannot legally do much here. Always crashes.
// Follow the rest of the code to get here.
}
// In MyUser.cpp
void LoginAndGetAssets(String^ email, String^ password){
Uri^ uri = ref new URI(MY_SERVER + "login.json");
String^ inJSON = "some json input data here"; // serialized email and password with other data
// make the HTTP request to login, then notify XAML that it has data to render.
_myService->HTTPPostAsync(uri, json).then([](String^ outputJson){
String^ assets = MyParser::Parse(outputJSON);
// The Login has returned and we have our json output data
if(_delegate)
{
_delegate->UpdateUI(assets);
}
});
}
// In MyService.cpp
task<String^> MyService::HTTPPostAsync(Uri^ uri, String^ json)
{
return _httpRequest.PostAsync(uri,
json->Data(),
_cancellationTokenSource.get_token()).then([this](task<std::wstring> response)
{
try
{
if(_httpRequest.GetStatusCode() != 200) SM_LOG_WARNING("Status code=", _httpRequest.GetStatusCode());
String^ j = ref new String(response.get().c_str());
return j;
}
catch (Exception^ ex) .......;
return ref new String(L"");
}, task_continuation_context::use_current());
}
Edit: BTW, the error I get when I go to update the UI is:
"An invalid parameter was passed to a function that considers invalid parameters fatal."
In this case I am just trying to execute in my callback is
txtBox->Text = data;
It appears you are updating the UI thread from the wrong context. You can use task_continuation_context::use_arbitrary() to allow you to update the UI. See the "Controlling the Execution Thread" example in this document (the discussion of marshaling is at the bottom).
So, it turns out that when you have a continuation, if you don't specify a context after the lambda function, that it defaults to use_arbitrary(). This is in contradiction to what I learned in an MS video.
However by adding use_currrent() to all of the .then blocks that have anything to do with the GUI, my error goes away and everything is able to render properly.
My GUI calls a service which generates some tasks and then calls to an HTTP class that does asynchronous stuff too. Way back in the HTTP classes I use use_arbitrary() so that it can run on secondary threads. This works fine. Just be sure to use use_current() on anything that has to do with the GUI.
Now that you have my answer, if you look at the original code you will see that it already contains use_current(). This is true, but I left out a wrapping function for simplicity of the example. That is where I needed to add use_current().
I'm currently using WCF in monotouch to call an existing service and a custom UIAlertView.
The problem is that if I create an UIAlertView as class instance and the I do the following:
public override void ViewDidAppear()
{
_alertView.Message = "Loading...";
_alertView.Show();
_client.GetDataAsync("test");
_client.GetDataCompleted += GetDataCompletedDelegate;
base.ViewDidAppear();
}
void GetDataCompletedDelegate(object sender, GetDataEventArgs)
{
// do someting with data
_alertView.Hide();
}
it works but this advice is written in console : UIAlertView: wait_fences: failed to receive reply: 10004003
else, if I try to run this code:
public override void ViewDidAppear()
{
using(CustomAV _alertView = new CustomAV())
{
_alertView.Message = "Loading...";
_alertView.Show();
_client.GetDataAsync("test");
_client.GetDataCompleted += delegate{
InvokeOnMainThread(delegate{
// do someting with data
_alertView.Hide();
});
};
}
base.ViewDidAppear();
}
the first time the code run, but now alert is shown. The second time the simulator can't startup. Couldn't register "com.yourcompany.wcftest" with the bootstrap server. Error: unknown error code. This generally means that another instance of this process was already running or is hung in the debugger.StackTrace. In this case I have to reboot the machine.
Thank you in advance.
EDIT:
Thank you Geoff, I've checked my code and into GetDataCompletedDelegate I've inserted a function that runs inside the UI Thread.
InvokeOnMainThread(delegate{
doSomething();
});
private void doSomething()
{
// do stuff here
_alertView.Hide();
}
The fency error continues to appear. If I use your solution inside doSomething() method, it works
_alertView.InvokeOnMainThread(delegate{
_alertView.Hide();
});
Why? Maybe I didn't understand, but in the first snippet of code do something() works in the UI thread!! Isn't true?
You have 2 seperate problems here.
1: _alertView.Hide () is not running on the UI thread (this is what causes the fences error)
2: In your second example you're disposing the UIAlertVeiw immediately after creating it, but you have a instance delegate dangled off it. This crashes the runtime in a hard way, and then when you run it again since the old crashed process is still running the simulator wont let you start a second instance.
Use case #1 but do _alterView.InvokeOnMainThread (delegate { _alertView.Hide (); });