My doubt is when we navigate from one page to another page in WinRT the Constructor() and On Navigated to() methods are called.
Can we restrict the constructor calling.
As my requirement is i have to attach a new object to the datacontext while navigating again.
You can't create an object without calling its constructor. You can set the DataContext in OnNavigatedTo().
Related
I want to create a controller based JavaFX GUI consisting of multiple controllers.
The task I can't accomplish is to pass parameters from one Scene to another AND back.
Or in other words:
The MainController loads SubController's fxml, passes an object to SubController, switches the scene. There shall not be two open windows.
After it's work is done, the SubController shall then switch the scene back to the MainController and pass some object back.
This is where I fail.
This question is very similar to this one but still unanswered. Passing Parameters JavaFX FXML
It was also mentioned in the comments:
"This work when you pass parameter from first controller to second but how to pass parameter from second to first controller,i mean after first.fxml was loaded.
– Xlint Xms Sep 18 '17 at 23:15"
I used the first approach in the top answer of that thread.
Does anyone have a clue how to achieve this without external libs?
There are numerous ways to do this.
Here is one solution, which passes a Consumer to another controller. The other controller can invoke the consumer to accept the result once it has completed its work. The sample is based on the example code from an answer to the question that you linked.
public Stage showCustomerDialog(Customer customer) {
FXMLLoader loader = new FXMLLoader(
getClass().getResource(
"customerDialog.fxml"
)
);
Stage stage = new Stage(StageStyle.DECORATED);
stage.setScene(
new Scene(
(Pane) loader.load()
)
);
Consumer<CustomerInteractionResult> onComplete = result -> {
// update main screen based upon result.
};
CustomerDialogController controller =
loader.<CustomerDialogController>getController();
controller.initData(customer, onComplete);
stage.show();
return stage;
}
...
class CustomerDialogController() {
#FXML private Label customerName;
private Consumer<CustomerInteractionResult> onComplete
void initialize() {}
void initData(Customer customer, Consumer<CustomerInteractionResult> onComplete) {
customerName.setText(customer.getName());
this.onComplete = onComplete;
}
#FXML
void onSomeInteractionLikeCloseDialog(ActionEvent event) {
onComplete.accept(new CustomerInteractionResult(someDataGatheredByDialog));
}
}
Another way to do this is to add a result property to the controller of the dialog screen and interested invokers could listen to or retrieve the result property. A result property is how the in-built JavaFX dialogs work, so you would be essentially imitating some of that functionality.
If you have a lot of this passing back and forth stuff going on, a shared dependency injection model based on something like Gluon Ignite, might assist you.
I've used AfterBurner.fx for dependency injection, which is very slick and powerful as long as you follow the conventions. It's not necessarily an external lib if you just copy the 3 classes into your structure. Although you do need the javax Inject jar, so I guess it is an eternal reference.
Alternately, if you have a central "screen" from which most of your application branches out you could use property binding probably within a singleton pattern. There are some good articles on using singleton in JavaFX, like this one. I did that for a small application that works really great, but defining all of those bindings can get out of hand if there are a lot of properties.
To pass data back, the best approach is probably to fire custom Events, which the parent controller subscribes to with Node::addEventHandler. See How to emit and handle custom events? for context.
In complex cases when the two controllers have no reference to each other, a Event Bus as #jewelsea mentioned is the superior option.
For overall architecture, this Reddit comment provides some good detail: https://www.reddit.com/r/java/comments/7c4vhv/are_there_any_canonical_javafx_design_patterns/dpnsedh/
I have an application that crashes when I call Close(this) in the viewmodel at level 2 (meaning can go back one page). One at level 3 (meaning can go back two pages) goes back fine.
I call this in the main app:
// Register the main view model
Mvx.RegisterSingleton<IMvxAppStart>(new MvxAppStart<StartScreenViewModel>());
In StartScreenViewModel I call
this.ShowViewModel<AddNewViewModel>();
And that viewmodel has a ICommand binding in the XAML that calls a function that calls:
this.Close(this);
When calling this Close(), I end up in the UnhandledException handler.
The exception message is:
The given key was not present in the dictionary.
at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsPage.LoadStateBundle(NavigationEventArgs e)
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsPage.<>c__DisplayClass1.<OnNavigatedTo>b__0()
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsExtensionMethods.<>c__DisplayClass1.<OnViewCreate>b__0()
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsExtensionMethods.OnViewCreate(IMvxWindowsView storeView, Func`1 viewModelLoader)
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsExtensionMethods.OnViewCreate(IMvxWindowsView storeView, MvxViewModelRequest viewModelRequest, Func`1 bundleLoader)
at Cirrious.MvvmCross.WindowsCommon.Views.MvxWindowsPage.OnNavigatedTo(NavigationEventArgs e)
What could cause this?
After some more digging and wondering about navigation, I figured it out.
I had overridden
OnNavigateFrom(...)
in the StartScreenViewModel, but had not called
base.OnNavigateFrom(...)
in the function body! Adding that called now allows navigation to work correctly. Noob!
I believe that by default Windows Store apps dispose of pages that are not on the top of the navigation stack. You can override this behaviour.
In my Windows Phone App there's a simple hierarchical model consisting of a class containing a collection of other domain objects.
In my xaml i have declared an ItemsContainer control that renders the items in the above mentioned collection as simple rectangles.
Now, at the VM level i have a structure that resembles my model with a parent VM having a collection of children VMs. Each child-VM encapsulates its own model.
Whenever the user taps the view bound to a child-VM a method of the parent-model object should be invoked taking the relevant child-model as parameter. This will in turn change some internal state that will be reflected (possibly) on all the child-views (not just the tapped one).
SO... given that i'm using the MVVM Light framework my current implementation is as follows:
Child-VM exposes a command
The command Execute method will use the messenger to notify the parent-VM of the tap event. The message (GenericMessage class) content will be the domain object encapsulated by the VM
The parent-VM executes the method of the parent-model using the message content as parameter
If the operation succeeds the parent-VM sends a new message to inform child-VMs of this fact. Once again the message content is the model object used as parameter in the method that was just invoked
Child-VMs raise a couple of PropertyChanged events that, finally, will update the bound views
It works but i fill it's a bit cumbersome. The thing that bugs me the most is the fact that when a child-view is tapped the associated VM will broadcast its encapsulated model object. Do you feel that there would be a better way of implementing such a system?
Thanks in advance for your precious help
Could you not just put the command on the parent viewmodel and pass the child viewmodel as the command parameter?
The parent view model can then just call methods on the child viewmodels to update them. I'm not sure I see the need for all these messages?
I have an Android app which uses a SupportActionBar that contains a bunch of tabs. These tabs each have a fragment that in turn are connected to a ViewModel in my core project. This works great and when i start the app they are all initialized right away and setup correctly.
What i would like to do is to call on a method on one of these ViewModels from my main activity that contains all the tabs and fragments.
I read in another post that in WP you could cast the DataContext to the ViewModel but that might not work in Android. I haven't been able to do this, maybe because my DataContext is not the currently displayed ViewModel but the MainViewModel connected to my main activity. Or maybe it's not supposed to be done that way, i'm not sure.
I'm trying to do this:
var test = (MessagesViewModel)this.DataContext;
test.GetViewDataFromApi();
To update the data in the view when i press the tab. I can't use the Init function for this for example since the ViewModel isn't recreated everytime i show the view.
Are you trying to update some data in the tab's fragment when tab is selected?
If that's the case, one way to do it is to
1) handle the tab selection event to get the current tab(maybe using TabListener),
2) get the fragment (MvxFagment) in the selected tab
3) get the (IMvxViewModel) view-model from the fragment
4) call the method you need to update data on the view-model
I assume you are using a MvxFragment (https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Droid.Fragging/Fragments/MvxFragment.cs?source=cc) so you can access the view-model from the MvxFragment's ViewModel property.
I am working on an AIR application:
The main window is like a dashboard. With the menu bar, I can open other windows with dashboard details. When I close these, I'd like to refresh the main window.
I tried to use an event listener, but the result is not good. If I open detail windows directly from the main window, I know how to add an event listener - and it works - but I don't know how to do it, if the detail window is opening from the menubar!
Thanks for helping me.
A Singleton is what you are looking for. Just put an event dispatcher inside and you will be able to listen from everywhere in the application.
A Singleton is like having a unique instance of an object in memory, so anyone modifying a variable inside that object ( or sending events throught ) will be modified for everyone.
Here is an example of code on how to use it.
http://life.neophi.com/danielr/2006/10/singleton_pattern_in_as3.html
Note: Singletons are powerful and dangerous at the same time, there is a lot of talk about how to use them, please read a little more about that if you are considering building a big project.
Hope it helps!
The issue is that you're performing business logic from a View. Don't do this. Instead, dispatch an event from each menu rather than directly opening the window from within it. Listen for those events at a higher level, and then you can either directly listen to the new windows you have opened, or you can create a base window Class that exposes a variable of type IEventDispatcher. If you populate that variable with the same event dispatcher, what you wind up with is called an "event bus," and you can listen on that for events.
This architecture requires a little more thought than using a Singleton, but it avoids the tight coupling and other issues you'll run into by introducing one into your project.
You can listen to an object (EventDispatcher) directly by adding an event listener to it, or if the dispatcher object is on the displaylist, such as a Sprite, you could listen at the stage level with the capture parameter set to true.
But the main caveat is that the dispatcher must be on stage for you to catch this event.
Your main window listens to stage (with capture = true):
stage.addEventListener("MY_CUSTOM_EVENT", handle_custom_event, true);
private function handle_custom_event(e:Event):void
{
var sub_window:Object = e.target;
// do something to your sub_window
}
Your sub window can dispatch events like this:
dispatchEvent(new Event("MY_CUSTOM_EVENT"));
But (ab)using the stage as a message passing infrastructure for custom events in this way is a little messy. You could consider a more formal message passing architecture if you really want this kind of communication. Even a static MessageBus class would at least quickly help you identify where you use this in your codebase. Either way, you'll have to be careful about references and memory leaks.