I have an application that consists from the following three modules:
Search (to search for objects)
List (to display the search results)
Painter (to allow me to edit objects) - this module isn't always loaded
(Each object is a figure that I can edit in the painter).
When I open an object in the painter it's added to the objects that are already in the painter and I can move it and alter it.
I'm using an object similar to the EventAggregator to communicate between the modules. For example, to show the search results I publish a "ShowList" event that is caught by the List module (I'm not sure this is the best way to do this, if anyone has better idea please comment...).
One of the features of the search module requires it to get the selected object in the painter (if the painter is available), and I'm not sure what would be the best way to do that...
I thought of these solutions:
Whenever the selected object in the painter changes it will publish a "PainterSelectedObjectChanged" event which will be caught by the search module and stored for later use.
When the selected object is needed by the search module it will publish a "RequestingPainterSelectedObject" event which will be caught by the painter module. The painter module will then set the "SelectedObject" property in the EventArgs object, and when the publish is complete and we're back in the search module we will have the painter's selected object in the EventArgs object.
What do you think? what is the right way to do this?
I would say, option A. It sounds like pretty usual scenario, maybe I didn't fully understood it as a whole. :)
I would say, option B. It sounds like pretty usual scenario, maybe I didn't fully understood it as a whole. :)
Related
When I use a map constructor like:
Person p = new Person(name: "Bob")
through something that is called via a grails.gsp.PageRenderer, the field values are not populated. When I use an empty constructor and then set the fields individually like:
Person p = new Person()
p.name = "Bob"
it succeeds. When I use the map constructor via a render call, it also succeeds.
Any ideas as to why this is the case?
Sample project is here in case anyone wants to dig deeper: https://github.com/danduke/constructor-test/
Actual use case, as requested by Jeff below:
I have a computationally expensive view to render. Essentially it's a multi-thousand page (when PDF'd) view of some data.
This view can be broken into smaller pieces, and I can reliably determine when each has changed.
I render one piece at a time, submitting each piece to a fixed size thread pool to avoid overloading the system. I left this out of the example project, as it has no bearing on the results.
I cache the rendered results and evict them by key when data in that portion of the view has changed. This is why I am using a page renderer.
Each template used may make use of various tag libraries.
Some tag libraries need to load data from other applications in order to display things properly (actual use case: loading preferences from a shared repository for whether particular items are enabled in the view)
When loaded, these items need to be turned into an object. In my case, it's a GORM object. This is why I am creating a new object at all.
There are quite a few opportunities for improvement in my actual use case, and I'm open to suggestions on that. However, the simplest possible (for me) demonstration of the problem still does suggest that there's a problem. I'm curious whether it should be possible to use map constructors in something called from a PageRenderer at all. I'm surprised that it doesn't work, and it feels like a bug, but obviously a very precise and edge case one.
"Technically it is a bug" (which is the best kind of bug!), and has been reported here: https://github.com/grails/grails-core/issues/11870
I'll update this if/when additional information is available.
My Flutter app has the following general structure:
The initial screen shows a list of contact objects. The user can tap a contact, which brings up
a detail screen that lets the user see the whole contact info, and modify any details temporarily. The user can either
dismiss the screen without saving the changes, or
tap a save button, which updates the contact permanently, and upon completion leads back to the initial screen.
I'm using FireStore. The list is built with Stream<QuerySnapshots>, and when the user taps an item, the app's router parses the route name (e.g. /contacts/123), creates the respective DocumentReference and forwards it to the detail screen's initializer, which then uses DocumentReference.get to load the details, and DocumentReference.updateData to save changes. Works beautifully – but is only a proof of concept.
Now I would like to hide FireStore and the remaining business logic behind a BLoC. This leads to some questions:
Keeping business logic out of the UI, as far as I understand it, implies that I should stick to named routes, and have the detail screen somehow use the route details to retrieve the relevant contact data through the BLoC. Is that true, and what's the best solution for this?
How can I subscribe to nested data using the BLoC? I want the detail screen to observe data changes, so that I can warn the user if the data becomes stale. Using functions on BLoCs (something like streamOfContact(contact) -> Stream<Contact>) is forbidden, so how would I do that with Sinks? Or is there generally a different way to do this without breaking the BLoC pattern? I'm very new to all of this, so may very well be I'm overlooking something important.
Similar question: How would I update a particular contact?
The tutorials I've found online only deal with root data (e.g. adding cart items to a cart, handling user authentication, ...), but I haven't seen an example showcasing nested data yet. Any help is highly appreciated!
1) Routing and navigation is in the responsibility of the UI layer. That means the UI layer must call Navigator.push[Named](...).
If it makes sense, you can move the logic that decides if the app should navigate to the detail screen:
// in the BLoC:
Stream<int> showContactDetail;
// in the UI layer:
bloc.showContactDetail.listen(_showContactDetail);
How you transfer the parameters to the detail route is totally up to you. You can use named routes, but it would be easier to transfer data with a builder:
void _showContactDetail(int contactId) {
Navigator.push(context, MaterialPageRoute(builder: (BuildContext context) {
return ContactDetailPage(
contactId: contactId,
);
}));
}
2) One BLoC should be tied to a single screen, that means there should be a separate BLoC for the detail screen (or dialog/sidebar/...), and you would pass the id of your contact to the second BLoC as a constructor parameter, or using a StreamSink, or using a simple setter method.
I would recommend you to use plain old methods instead of StreamSinks for the BLoC inputs. Here is a recent discussion about the topic.
3) The question is not only how to update your contact from the detail screen, but also how the detail BLoC obtains the contact data (if you are only transferring the contact id).
The answer: Another application layer, what I would call the data layer, that is shared between all BLoCs. You can store the data in Firebase, a sqlite database or a simple Map<int, Contact>.
The data layer would also propagate changes to the backend, and notify all BLoCs when the data has changed, probably using a Stream.
The next question that would come up is where you put this data layer (e.g. a class called ContactService):
You can create the ContactService in your ContactListPage, then pass it to the ContactDetailPage in a constructor parameter (using a route builder, as explained above). No magic here. A side effect that you may not want is that the service will be discarded when the list page is popped.
InheritedWidget that is above the MaterialApp, or at least above the Navigator generated by the MaterialApp (You can use the builder of MaterialApp to wrap the navigator with your own widgets). Putting it that high up in the tree ensures that all pages of your app can access it.
Using scoped_model, which is basically the same. Must also be inserted above the navigator to be accessible from both routes
A static variable/singleton
I've got a page where a DataTemplate is being used to bind to the model for that content, e.g.:
<DataTemplate x:DataType="models:MyDataType">
... content ...
</DataTemplate>
In that content, I need to be able to bind a Click event. I need that click event to exist in the view model that is set as the page's DataContext:
<Page.DataContext>
<vm:MyViewModel x:Name="ViewModel">
</Page.DataContext>
but I'm really struggling with getting it to compile. Every approach I try results in the compilation error "Object reference not set to an instance of an object".
I know I can't use x:Bind because that will bind to the DataTemplate's DataContext, so I've been trying to use Binding and, based on other SO answers I've read, it seems like the answer should be:
Click="{Binding DataContext.Button_Click, ElementName=Page}"
where Page is defined as the x:Name for the Page. I've tried removing DataContext. I've tried adding ViewModel.
What am I misunderstanding? Is it not possible to do what I want to do? I've tried using code-behind instead but I'm using Template 10 and that pushes almost everything onto the view model, which makes it harder for me to access things like the navigation service from code-behind.
tl;dr; use Messaging.
#justinXL is right, 'ElementName' can work. But is it best?
The problem you are trying to solve has already been solved with messaging. Most MVVM implementations include a messaging solution. Prism uses PubSubEvents; MVVM Light has its own messenger. There are others, too.
The idea is that an outside class, typically described as a message aggregator, is responsible for statelessly receiving and multicasting messages. This means you need to have a reference to the aggregator but not a reference to the sender. It’s beautiful.
For example
A common use case might be a mail client and how the data template of a message in the list would include a trash/delete button. When you click that button, what should be called? With messaging, you handle the button_press in the model and send/publish a message (one that passes the item).
The hosting view-model has subscribed to the aggregator and is listening for a specific message, the Delete message that we just sent. Upon receipt, it removes it from the list and begins the process to delete it from cache/database, or whatever – including prompting the user with “Are you sure?”
This means all your data binding in your data template is local, and does NOT extend outside its local scope. Why does this matter? Because if you use Element Binding to reach the hosting page, it means you cannot 1) move this template to a resource dictionary or 2) reuse this template.
There are two other reasons.
you cannot use compiled x:Bind to do this because it already limits use of this painful binding approach – this matters because a data template is typically in a list, and performance should always be prioritized, and
It adds considerable complexity.
Complexity?
I am a big fan of sophisticated solutions. I think they are rare and are the trademark of truly smart developers. I love looking at such code/solutions. Complex is not the same as sophisticated. When it comes to complexity, I am not a fan. Data binding is already difficult to wrap your head around; multi-sourcing your data binding across scope boundaries is pure complexity.
That’s what I think.
Your binding expression is correct, except it won't work with a Button_Click event handler. You will need an ICommand defined in your page's ViewModel.
Since you are using Template10, you should be able to create a DelegateCommand called ClickCommand like this
private DelegateCommand<MyDataType> _clickCommand;
public DelegateCommand<MyDataType> ClickCommand
{
get
{
_clickCommand = _clickCommand ?? new DelegateCommand<<MyDataType>>((model) =>
{
// put your logic here.
});
return _clickCommand;
}
}
And the binding will be updated to
<Button Command="{Binding DataContext.ClickCommand, ElementName=Page}" CommandParameter="{x:Bind}" />
Note I have also added a CommandParameter binding to the button as you might want to know which MyDataType instance is associated with the clicked button.
If you were to code a function/method that would, for entered string or slug (for instance in Create or Edit view), go into datastore and check whether that string or slug exists and in this case create a link to it, where would you put it?
For instance, we have a "Link" textbox on our Create or Edit form. I have a jQuery autocomplete wired to it, which retrieves existing Page slugs. If a user decides to select one of them, we would create a link that points to the content within our site, based on the Page controller, like this:
~/Page/Display/some-slug
or just
~/Page/some-slug
If, however, user decides not to select anything and inputs for instance www.google.com, we catch it in our ParseUrl(), format it with http://... etc. and store it like that.
The code for the function is no problem and I have it working currently in a Model Binder. However, due to strange, confusing and opposing practices with DI in Model Binders I would like to move it somewhere else. Another reason would be to remove dataccess code from Model Binders.
The question is - where to move such funcionality? If possible, I would like to avoid repeating ParseUrl() calls across various controller actions.
1) Implement it so it makes sense to you and your team.
-or-
2) Leave it where it is because its already working.
Is moving it going to make your app better, will your customers be happier, deadlines met faster?
There is no magic Asp.net MVC thunder-god that descends from the heavens to smite you if you dare use the wrong extensibility point. Nobody is going to call you an idiot. People may disagree, but that happens. Its ok to "go for it" and get things done before being architecturally pure.
"However, due to strange, confusing and opposing practices with DI in Model Binders"
What does that even mean?
This is probably a very "dumb" question for whoever knows VirtualShellTools but I only started using it and couldn't find my answer in the demos' code. Please note that I'm also unfamiliar with virtualtreeview.
I use a VirtualExplorerTreeview to display a directory structure, linked with a VirtualExplorerListview to display a certain type of files in the selected directory as well as specific informations about them
I've been able to point them at the right place, link them as I wanted, filter everything in the listview, and looking at the demos I have a pretty good idea about how to add my own columns and draw it to display my custom data.
My issue lies with the Treeview: I would like to sort the directories displayed in the order I want; specifically, I want "My Docs" and other folder to appears first, then drives, then removable media. Looking in the TNamespace property I found how to distinguish them (Directory and Removable properties), but I don't know how to implement my own sort/what event I need. I tried CompareNode but that doesn't even seem to be called.
If you want to do everything yourself, then set toUserSort in the TVirtualExplorerTree.TreeOptions.VETMiscOptions property. That causes the control to just use the DoCompare method inherited from the virtual tree view, and that should call the OnCompareNodes event handler.
A better way is to provide a custom TShellSortHelper. Make a descendant of that class and override whichever methods you need. Create an instance of that class and assign it to the tree's SortHelper property. (The tree takes ownership of the helper; free the old one, but not the new one.) If the items are being sorted on a column that that class doesn't know how to compare, then handle the tree's OnCustomColumnCompare event.
To help you figure out exactly which methods you need to override or events you need to handle, set a breakpoint in TCustomVirtualExplorerTree.DoCompare and step through to see what gets called in various situations.