I have searched the web for the correct answer, but I've been failing to achieve this :
In EntryPoint class, I need to manage widgets according to events that occur in nested widgets. I've cleaned of the code to focus only on what is important here.
I have built a few UiBinder widgets, for example, a Login pane where the user can enter his credentials. In my EntryPoint class, I add the widgets in the correct position.
// This is from EntryPoint class
public void onModuleLoad() {
LoginPane lp = new LoginPane();
RootPanel.get("headerRightPane").add(lp);
lp.setFocus();
// Other widgets added in same manner after this point...
}
I would like a successful login to remove the LoginPane and replace it by another widget (AccountPane) that would show the account information for the user that is logged in. I have an onClick event, in LoginPane, that sends a request to a fully functional Servlet that checks the credentials. At this exact point, if the Servlet determines that the login is indeed successful, I would like to fire a "successfulLogin" event (from LoginPane) that could notify the EntryPoint class that the LoginPane can now be replaced by the AccountPane.
// This is from LoginPane class
#UiHandler("loginButton")
void onClick(ClickEvent e) {
checkCredentials(usernameField.getText(), passwordField.getText());
}
public void checkCredentials(String username, String password) {
String usernameToServer = username;
String passwordToServer = password;
credentialsService.credentialsServer(usernameToServer, passwordToServer,
new AsyncCallback<CredentialsPaneContent>() {
public void onFailure(Throwable caught) {
answerLabel.setText(Utilities.SERVER_ERROR);
}
public void onSuccess(CredentialsPaneContent result) {
if ( result == null ) {
answerLabel.setText("Login Failed.");
} else {
// Fire event here (to be caught by EntryPoint class)
answerLabel.setText("Login Successful.");
}
}
});
}
So, the question : How should I proceed to create, fire and listen to the event from my nested widget?
Use an EventBus. Additionally, consider adopting the Model-View-Presenter pattern to keep your application maintainable as it grows:
Large scale application development and MVP, Part I
Large scale application development and MVP, Part II
GWT MVP Development with Activities and Places
Lets have an interface which is implemented by EntryPoint class,
now have a referrence of interface type which actually an object of interface.
Using this interface referrence invoke the listner(interface) mothod, which serves your purpose.
Related
I am monitoring the user's location every 15 minutes and I just want the application to continue sending the location even if the user closes the application in the taskbar.
I tried this sample but it's in Xamarin.Android https://learn.microsoft.com/en-us/xamarin/android/app-fundamentals/services/foreground-services i have to create a dependencyservice but i don't know how.
i have to create a dependencyservice but i don't know how.
First, create an Interface in the Xamarin.forms project:
public interface IStartService
{
void StartForegroundServiceCompat();
}
And then create a new file let's call it itstartServiceAndroid in xxx.Android project to implement the service you want:
[assembly: Dependency(typeof(startServiceAndroid))]
namespace DependencyServiceDemos.Droid
{
public class startServiceAndroid : IStartService
{
public void StartForegroundServiceCompat()
{
var intent = new Intent(MainActivity.Instance, typeof(myLocationService));
if (Android.OS.Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.O)
{
MainActivity.Instance.StartForegroundService(intent);
}
else
{
MainActivity.Instance.StartService(intent);
}
}
}
[Service]
public class myLocationService : Service
{
public override IBinder OnBind(Intent intent)
{
}
public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
{
// Code not directly related to publishing the notification has been omitted for clarity.
// Normally, this method would hold the code to be run when the service is started.
//Write want you want to do here
}
}
}
Once you want to call the StartForegroundServiceCompat method in Xamarin.forms project, you can use:
public MainPage()
{
InitializeComponent();
//call method to start service, you can put this line everywhere you want to get start
DependencyService.Get<IStartService>().StartForegroundServiceCompat();
}
Here is the document about dependency-service
For iOS, if the user closes the application in the taskbar, you will no longer be able to run any service. If the app is running, you can read this document about ios-backgrounding-walkthroughs/location-walkthrough
You might want to have a look at Shiny by Allan Ritchie. It's currently in beta but I would still suggest using it, as it will save you a lot of trouble writing this code yourself. Here's a blog post by Allan, explaining what you can do with Shiny in terms of background tasks - I think Scheduled Jobs are the thing you're looking for.
I am having an MvvmCross ViewModel, which calls different async methods of my DataService.
Similar to the following:
public class LoginViewModel : MvxViewModel
{
private readonly IIdentityService _dataService;
private CancellationTokenSource _viewModelCancellationTokenSource;
public IMvxCommand GoLogin { get; set; }
public LoginViewModel(IIdentityService identityService)
{
_dataService = identityService;
_viewModelCancellationTokenSource = new CancellationTokenSource();
GoLogin = new MvxCommand(async () => await ProcessLogin());
}
private async Task ProcessLogin()
{
// calling the dataservice which must stop processing
// (to cancel) in case if the ViewModel is being destroyed
await _dataService.AssureIsLoggedIn(data, _viewModelCancellationTokenSource.Token);
await NavigationService.Navigate<LoginNextStepViewModel>();
}
public override void ViewDestroy(bool viewFinishing = true)
{
base.ViewDestroy(viewFinishing);
// not sure if that is a right (and working) place
_viewModelCancellationTokenSource.Cancel();
}
}
So, MvvmCross is quite unclear about the part with the ViewModel destroying. It describes Construction, Init, Reload and Start, but doesn't say any definite regarding the destroying:
Monitoring other View/ViewModel lifecycle event across multiple
platforms is fairly tricky, especially once developers start
experimenting beyond the ‘basic’ presentation models and start using
tabs, splitviews, popups, flyouts, etc
For most viewmodels, it’s common to not try to monitor other lifecyle
events. This is OK since most viewmodels don’t perform any actions and
don’t consume any resources when the view is not present - so these
can just be left to be garbage collected when the system needs the
memory back.
However, besides the custom platform situations, there are still many cases like navigating back from the view model, or (again) navigation away from current viewmodel with its following closing.
So, what's the best way to handle it then?
From your code:
// calling the dataservice which must stop processing
// (to cancel) in case if the ViewModel is being destroyed
The ViewModel won't be destroyed before the async methods finish executing. I think you are confusing the View with the ViewModel.
In case of a login page, you would usually prevent the user from navigating away from it until your server call goes through.
If for some reason you want to cancel then you need to decide what scenarios you want to handle, there is no single universal place. Your options are the view callbacks:
void ViewDisappearing();
void ViewDisappeared();
void ViewDestroy();
and the navigation events:
event BeforeNavigateEventHandler BeforeNavigate;
event AfterNavigateEventHandler AfterNavigate;
event BeforeCloseEventHandler BeforeClose;
event AfterCloseEventHandler AfterClose;
event BeforeChangePresentationEventHandler BeforeChangePresentation;
event AfterChangePresentationEventHandler AfterChangePresentation;
I developed a JavaFX application using MVC and DAO patterns. From the user interface the user can press a button to start export from MS Access to SQLite. This may take a long time, so I created a task (in the Controller). The task invokes a method of the Model "exportFromAccessToSQLite". All the logic of the database is in the Model. It all works fine. But I'd like to add a button in the user interface which when pressed stops the current operation. I would like to enter the code in the controller. How can I do?
The code is this:
Model objModel = new Model();
Task worker = new Task() {
#Override
protected Void call() throws Exception {
objModel.exportFromAccessToSQLite(fileAccess, directoryDest);
updateProgress(1, 1);
return null;
}
};
prgEspIndicator.progressProperty().bind(worker.progressProperty());
new Thread(worker).start();
Is there a way to pass data to dependencies registered with either Execution Context Scope or Lifetime Scope in Simple Injector?
One of my dependencies requires a piece of data in order to be constructed in the dependency chain. During HTTP and WCF requests, this data is easy to get to. For HTTP requests, the data is always present in either the query string or as a Request.Form parameter (and thus is available from HttpContext.Current). For WCF requests, the data is always present in the OperationContext.Current.RequestContext.RequestMessage XML, and can be parsed out. I have many command handler implementations that depend on an interface implementation that needs this piece of data, and they work great during HTTP and WCF scoped lifestyles.
Now I would like to be able to execute one or more of these commands using the Task Parallel Library so that it will execute in a separate thread. It is not feasible to move the piece of data out into a configuration file, class, or any other static artifact. It must initially be passed to the application either via HTTP or WCF.
I know how to create a hybrid lifestyle using Simple Injector, and already have one set up as hybrid HTTP / WCF / Execution Context Scope (command interfaces are async, and return Task instead of void). I also know how to create a command handler decorator that will start a new Execution Context Scope when needed. The problem is, I don't know how or where (or if I can) "save" this piece of data so that is is available when the dependency chain needs it to construct one of the dependencies.
Is it possible? If so, how?
Update
Currently, I have an interface called IProvideHostWebUri with two implementations: HttpHostWebUriProvider and WcfHostWebUriProvider. The interface and registration look like this:
public interface IProvideHostWebUri
{
Uri HostWebUri { get; }
}
container.Register<IProvideHostWebUri>(() =>
{
if (HttpContext.Current != null)
return container.GetInstance<HttpHostWebUriProvider>();
if (OperationContext.Current != null)
return container.GetInstance<WcfHostWebUriProvider>();
throw new NotSupportedException(
"The IProvideHostWebUri service is currently only supported for HTTP and WCF requests.");
}, scopedLifestyle); // scopedLifestyle is the hybrid mentioned previously
So ultimately unless I gut this approach, my goal would be to create a third implementation of this interface which would then depend on some kind of context to obtain the Uri (which is just constructed from a string in the other 2 implementations).
#Steven's answer seems to be what I am looking for, but I am not sure how to make the ITenantContext implementation immutable and thread-safe. I don't think it will need to be made disposable, since it just contains a Uri value.
So what you are basically saying is that:
You have an initial request that contains some contextual information captured in the request 'header'.
During this request you want to kick off a background operation (on a different thread).
The contextual information from the initial request should stay available when running in the background thread.
The short answer is that Simple Injector does not contain anything that allows you to do so. The solution is in creating a piece of infrastructure that allows moving this contextual information along.
Say for instance you are processing command handlers (wild guess here ;-)), you can specify a decorator as follows:
public class BackgroundProcessingCommandHandlerDecorator<T> : ICommandHandler<T>
{
private readonly ITenantContext tenantContext;
private readonly Container container;
private readonly Func<ICommandHandler<T>> decorateeFactory;
public BackgroundProcessingCommandHandlerDecorator(ITenantContext tenantContext,
Container container, Func<ICommandHandler<T>> decorateeFactory) {
this.tenantContext = tenantContext;
this.container = container;
this.decorateeFactory = decorateeFactory;
}
public void Handle(T command) {
// Capture the contextual info in a local variable
// NOTE: This object must be immutable and thread-safe.
var tenant = this.tenantContext.CurrentTenant;
// Kick off a new background operation
Task.Factory.StartNew(() => {
using (container.BeginExecutionContextScope()) {
// Load a service that allows setting contextual information
var context = this.container.GetInstance<ITenantContextApplier>();
// Set the context for this thread, before resolving the handler
context.SetCurrentTenant(tenant);
// Resolve the handler
var decoratee = this.decorateeFactory.Invoke();
// And execute it.
decoratee.Handle(command);
}
});
}
}
Note that in the example I make use of an imaginary ITenantContext abstraction, assuming that you need to supply the commands with information about the current tenant, but any other sort of contextual information will obviously do as well.
The decorator is a small piece of infrastructure that allows you to process commands in the background and it is its responsibility to make sure all the required contextual information is moved to the background thread as well.
To be able to do this, the contextual information is captured and used as a closure in the background thread. I created an extra abstraction for this, namely ITenantContextApplier. Do note that the tenant context implementation can implement both the ITenantContext and the ITenantContextApplier interface. If however you define the ITenantContextApplier in your composition root, it will be impossible for the application to change the context, since it does not have a dependency on ITenantContextApplier.
Here's an example:
// Base library
public interface ITenantContext { }
// Business Layer
public class SomeCommandHandler : ICommandHandler<Some> {
public SomeCommandHandler(ITenantContext context) { ... }
}
// Composition Root
public static class CompositionRoot {
// Make the ITenantContextApplier private so nobody can see it.
// Do note that this is optional; there's no harm in making it public.
private interface ITenantContextApplier {
void SetCurrentTenant(Tenant tenant);
}
private class AspNetTenantContext : ITenantContextApplier, ITenantContext {
// Implement both interfaces
}
private class BackgroundProcessingCommandHandlerDecorator<T> { ... }
public static Container Bootstrap(Container container) {
container.RegisterPerWebRequest<ITenantContext, AspNetTenantContext>();
container.Register<ITenantContextApplier>(() =>
container.GetInstance<ITenantContext>() as ITenantContextApplier);
container.RegisterDecorator(typeof(ICommandHandler<>),
typeof(BackgroundProcessingCommandHandlerDecorator<>));
}
}
A different approach would be to just make the complete ITenantContext available to the background thread, but to be able to pull this off, you need to make sure that:
The implementation is immutable and thus thread-safe.
The implementation doesn't require disposing, because it will typically be disposed when the original request ends.
I'd like to pair a Model with it's View through an interface. I want to control when and how often the view is updated. So something like PropertyChangeListener wouldn't work well (where an event is fired after each property is set).
I'm not developing for a specific GUI framework. The goal here is the ability to swap out different GUI front ends (right now for testing, but might be useful later for different versions of the app). These might be Swing, or it might be a web browser (via GWT, for example).
Below is my approach. The view implements an interface to provide a method to update. This is triggered by the controller when it determines it's done updating the model. This still feels ok to me, since the Controller is only interacting with the view through the model, the controller is not dependent on a particular implementation of the View.
So, I guess my question(s) are
does this work well?
Is this standard practice?
Does this pattern have a name?
Rough code sample (Java):
// Controller, manages Items (the model)
class ItemList {
void addItem(Item item) {
}
void doStuffWithItems() {
// perform some set of operations, such as sorting or layout
for (Item item : items) {
// ....
}
// now with everything in it's final position:
for (Item item : items) {
item.updateView();
}
}
}
// Model
class Item {
private int top;
private int left;
private int width;
private int height;
// Can remember it's previous position/size:
public void savePostion() {
}
// And recall it for the Controller to use:
public public Position getSavedPosition() {
}
// Plus some other useful functions:
public boolean intersectsWith(Item other) {
}
public void updateView() {
this.view.update();
}
void setView(ItemView view) {
this.view = view;
}
}
// Interface used by View implementations
public interface ItemView {
// Trigger the view to reflect the current state of the model
void update();
}
// Example, as a Swing component
class ItemComponent extends JComponent implements ItemView {
private Item item;
public ItemComponent(Item item) {
this.item = item;
item.setView(this);
}
// ItemView#update
public void update() {
// update the component's size/position
setBounds(new Rectangle(item.getLeft(), item.getTop(), item.getWidth(), item.getHeight()));
}
#Override
public void paint(Graphics g) {
// ...
}
}
I would avoid forcing the View to implement an interface only for change notification. Create a separate "update now" event on the model instead.
The model should not be controlling or know about the view directly. The view should register a callback with the controller so the controller can tell the view when to update, that's why its the controller. You could have the model allow external listeners for a modelChangedEvent. Then the view could register with the model in that respect without the model knowing there was a view. See the J2EE blueprint for MVC and how there is an indirect event notification of state change in the model.
For traditional applications that run on the desktop of a computer I recommend variants of the Passive View. The class responsible for creating and managing the form is a thin shell that passes events to the UI Object. The UI_Object interact with the form via a interface. In term the UI Object implements a UI_View Interface and registers itself with a View Controller that is situated lower in the object hierarchy.
The UI_Object then execute object implementing the Command Pattern which modifies the model. The command object can interacts with the various views via the interfaces exposed by the View Control.
What this does is allow you to rip off the form classes and replace them with stub classes that implement the form interfaces. The stub classes are used for automated testing especially for integration tests.
The interfaces precisely define the interaction between the Form, the UI_Object, Commands and the views. They can be designed to be relatively language agnostic so they can make porting between platform easier.
What you are missing in your example are command objects. You need this structure
ItemViewForms
ItemViewImplementation
ItemViewFormInterface
ItemViewCommands
ItemViewInterface
MyModel
Incorporate ItemList in the ItemViewImplementation
ItemComponent would register with the ItemViewImplementation using the ItemViewInterface.
The sequence of events would look something like this
User wants to update the Item
Clicks on the UI (assuming that UI
involves clicking with a mouse)
The Form tells the
ItemViewImplementation through the
ItemViewInterface that X has been
done with Y parameters.
The ItemViewImplementation then
creates a command object with the
parameters it needs from Y.
The Command Object take the Y
Parameters modifies the model and
then tells the
ItemViewImplementation through the
ItemViewInterface to update the UI.
The ItemViewImplementation tells the
ItemViewForms to update the UI
through the ItemViewFormInterface.
The ItemViewForms updates.
The advantage of this approach is that the interaction of each layer is precisely defined through interfaces. The Software ACTIONS are localized into the command objects. The Form layers is focused on display the result. The View layer is responsible for routing actions and response between the Commands and Forms. The Commands are the only things modifying the model. Also you have the advantage of ripping off the Forms Implementation to substitute any UI you want including mock object for unit testing.