Subclassing a Fabricjs object is working fine, and is particularly useful for making custom composite objects by subclassing fabric.Group.
But is it possible to subclass the subclass ? I have not managed so far.
If my first subclass is created by:
var Custom = fabric.util.createClass(fabric.Group, { ...
I expected the second level subclass to be created by:
var MoreCustom = fabric.util.createClass(Custom, { ...
Any other way to achieve this ? Or subsubclassing is just to be avoided ?
Related
This question already has answers here:
swiftui how to fetch core data values from Detail to Edit views
(2 answers)
Closed 11 months ago.
I try to use core data to store persistent data on an iOS device. I've got user flows to create and edit domain objects with a few related and deeply nested objects.
Those user flows are very similar, so I would like to use the same views for those tasks, just deciding on appear if the view got an existing domain object passed or it needs to create a new one.
After testing different approaches, nothing seems to fit this context so I wonder if there are recommended ways for this situation?
The following options got tested:
initializing the core data object in init() results in an Modifying state during view update, this will cause undefined behavior. warning
initializing the core data object in .onAppear requires the #ObservedObject var domainObjectPassed: DomainObject to be optional, not quite what I'm looking for as well
Any suggestions?
Already did that. I extracted the same logic into one view and have two distinct wrapper views that should handle this problem. But I've got the same situation one level higher.
struct CreateView: View {
#ObservedObject private var domainObject: DomainObject
init(moc: NSManagedObjectContext) {
domainObject = DomainObject(context: moc)
domainObject.id = UUID()
try? moc.save()
}
var body: some View {
CustomizeView(domainObject: domainObject)
}
}
-> results in warning from the first option
struct CreateView: View {
#Environment(\.managedObjectContext) var moc
#ObservedObject private var domainObject: DomainObject? = nil
var body: some View {
CustomizeView(domainObject: domainObject)
.onAppear {
...
}
}
}
-> requires domainObject in CustomizeView to be optional, not what I'm looking for
I am using the same concept (one view for editing and creating), but in my case I find myself comfortable using an optional to get the core data object. If you can live with an optional, this could work.
In this way, you just need to check if the object passed is nil: if it is, create the object, otherwise use the object passed.
In a very schematic way, the view could be:
struct EditOrCreate: View {
var coreDataObject: MyCoreDataEntity
// Optional object at initializer
init(objectPassed: MyCoreDataEntity? = nil) {
if objectPassed == nil {
coreDataObject = MyCoreDataEntity(context: thePersistentContainerContext)
} else {
coreDataObject = objectPassed!
}
}
var body: some View {
// All the text fields and save
}
}
When creating, just call EditOrCreate().
When editing, just pass the object: EditOrCreate(objectPassed: theObjectBeingShown).
You can also make coreDataObject an optional variable (which is what I did in my code), depending on how you want to handle your logic - for example, to cancel the creation before saving: in that case, you need to check for nil after the user has confirmed the creation of the new object.
Some programmers believe that "Premature Optimization Is the Root of All Evil". What I've seen happens when creating generic view code with only a small number of cases that have not yet been thought through is that after creating the generic version, you realise that you need to customise one of them, so end up trying to override the default behaviour in certain cases, which gets real messy and you would have been better off just with separate versions in the first place.
In SwiftUI, the View structs are lightweight and there is no issue with creating lots of them. Try to break your View structs up to be as small as possible then you can compose them together to form your different use cases.
The time you save could be spent on learning more about how SwiftUI works and fixing the issues in the code you posted. E.g. we don't init objects in the View struct init, or in body. Those need to run fast because that code runs quite frequently and creating objects is a comparably heavy task, also those objects that are created are immediately discarded after SwiftUI has finished building the View struct hierarchy, diffed it from last time, and updated the actual UIKit Views on screen. I highly recommend watching every WWDC SwiftUI video, there is a lot to learn and there is a lot of magic going on under the hood.
Another thing you could spend time learning is Swift generics and protocols. These are powerful ways to build reusable code using value types instead of class inheritance that we would typically use as ObjC/UIKit developers which tends to be buggy. You can read more about here: Choosing Between Structures and Classes (Apple Developer)
I've got a rendering engine, much like React where I need to store classes rather than instances in an object for compiling.
So for example, I have a Button component that I would like to be able to dynamically instantiate. Doing this would be as easy as
new components["Button"]
For this, I need a list of all possible classes. So I've got a Dictionary interface declared like so:
interface Dictionary<T> {
[Key: string]: T;
}
This works well, I'm easily able to add objects to this dictionary. Except if I have an object:
const components: Dictionary<Component> = {
Button: Button
}
Then I get an error because Button is a class, rather than an instance. Here, the issue is, I don't want to define the dictionary as Dictionary<Function> because that would mean I allow any function into the dictionary. Specifically, I only want to allow classes into the dictionary that extend the Component class.
How would I achieve this?
You also need to define the signature of the constructor (which makes sense if you think about it), but you do the following:
interface ComponentClass {
new (a: number): Component;
}
(The signature of the constructor is probably not "number", but put in whatever it is.)
I have a problem with implementing following scenario using Xamarin.iOS and MvvmCross (6.2.3.0). I have a view and in it's viewmodel I have a property which is a list of objects. I need to dynamically generate a label and a textfield for each of this list entry on my view. So I decided to implement a custom view for this. Here is what I tried so far:
In my viewcontroller, in CreateView I simply add my custom UIView. I can see it's content on my view. In ViewDidLoad() I create bindings:
private void CreateBindings()
{
var set = this.CreateBindingSet<MyController, MyViewModel>();
set.Bind(myCustomControl).For(x => x.DataContext).To(vm => vm.MyListOfObjects);
set.Apply();
}
MyCustomControl code is as follows:
public class MyCustomControl : MvxView
{
public MyCustomControl() {
//DataContext is always null here!
//I'd like to get access to list of objects here, add controls for each entry and make sure they are binded to a viewmodel's list of objects somehow.
}
}
I noticed that the list of objects in my viewmodel is set later than a constructor call for MyCustomControl is being made, so it makes sense that DataContext in MyCustom control is null. I'm missing something obvious I believe. Can someone point me in a proper direction? I would be very grateful.
I tried this example, which is exactly what I'm trying to achieve, but no luck so far ;(
N=32 - ViewModels and MvxView on the iPad - N+1 days of MvvmCross
https://www.youtube.com/watch?v=cYu_9rcAJU4&list=PLR6WI6W1JdeYSXLbm58jwAKYT7RQR31-W&index=35&t=1649s
Take a look at 23:43 of the video you posted.
You should do the view binding inside a DelayBind method.
this.DelayBind(() => {
var set = this.CreateBindingSet<MyCustomControl, MyItemViewModel>();
set.Bind(badgeLabel).For(v => v.Text).To(x => x.BadgeText);
set.Bind(topSummary).For(v => v.Text).To(x => x.TopSummary);
set.Bind(bottomSummary).For(v => v.Text).To(x => x.BottomSummary);
set.Bind(this.Tap()).For(v => v.Command).To(x => x.Edit);
set.Apply();
});
MvvmCross will do the binding for you.
Also Mind that the proper types have to be passed to CreateBindingSet.
On a side node, MvvmCross N+1 videos are from 2013 and some things has changed since then.
You can find some good examples there but sometimes it just won't work anymore.
If you are new to MvvmCross, download the source code of Playground project for reference:
https://github.com/MvvmCross/MvvmCross/tree/develop/Projects/Playground
and join the #mvvmcross slack channel if you need more help
https://xamarinchat.herokuapp.com/
MvvmCross is really great... once you grasp the basic concepts.
As I exposed here, I would like to be able to query freely on the index without Orchard building the query for me.
I built a module, and inserted a copy of the SearchController, adding a new route...
To override default Orchard behavior concerning the query, I had to create new implementations of : ISearchService, IIndexManager, ISearchBuilder, IIndexProvider.
There are minor modifications from their default implementations, but they are needed.
That works as expected, but it currently override the default search too.
This is because I used the same interfaces and autofac takes my implementations.
I would like to be able to leave the default implementation untouched (at url /Search), and add my implementation at url (/LuceneSearch for example)
I suppose I must tell Autofac to use my implementations only for my controller by creating a class that inherits the autofac Module class.
Here is my problem : I don't know how to tell Autofac to use by default the Orchard Implementation, and just for my controller, use my implementation....
Another possibility is to create new interfaces, but it seems to me not really beautiful...
Can someone help me ? :)
Metadata feature will help you here. Also you have to register your implementations with PreserveExistingDefaults() modifier to preserve orchard's implementations by default.
Update:
Orchard registers all dependencies from Autofac's IModule implementation and from Orchard's IDependency one. All magic happen in Orchard's ShellContainerFactory class. Since ISearchService inherits from IDependency your implementation is registered by Orchard which overwrites default one.
You have two ways here:
Introduce your own empty interface IMySearchService which inherits from ISearchService. Implement and use it in your code where you need your implementation. Orchard will handle all registrations for your.
Orchard registers all IDependency implementations with "Feature" Metadata in ShellContainerFactory.RegisterType method. You can read this metadata in your code and choose your implementation (see link to wiki above). Feature class contains all necessary information about your module.
Hope this will help you.
A simpler method without dabbling with the intricacies of Autofac would be to use an IEnumerable<IInterface> variable in your controller/driver at url "/LuceneSearch" to hold all implementations of IInterface and choose which to consume.
For example, in order to consume your implementation of IIndexManager, you would put the following in your controller or driver
public class MyCustomPartDriver : ContentPartDriver<MyCustomPart> {
private readonly IEnumerable<IIndexManager> _indexManagers;
public MyCustomPartDriver(IEnumerable<IIndexManager> indexManagers) {
_indexManagers = indexManager;
}
protected override DriverResult Display(MyCustomPart part, string displayType, dynamic shapeHelper) {
//Use your implementation of IIndexManager
var indexManager = _indexManagers.First(im => im is MyCustomIndexManager);
//Get the ISearchBuilder from your implementation of IIndexManager
var searchBuilder = indexManager.HasIndexProvider() ? indexManager.GetSearchIndexProvider().CreateSearchBuilder("Search") : new NullSearchBuilder();
//perform search on the indexing engine
var contentItemIds = searchBuilder.
.WithField("type", "MyCustomType").Mandatory().ExactMatch()
.Parse("mycustompart-keyword", part.Keyword).Mandatory()
.Search()
.Select(h => h.ContentItemId)
.ToList();
//do stuff with the results returned and return a DriverResult using the ContentShape method. Well, you know the drill.
}
}
If you don't want to have autofac resolve your own implementation by default, then don't implement the public interface.
I have a question that keeps bothering me. Currently, I have started using Kohana 3.2 Framework. I've written a helper to handle some functionality - I have a number of methods, which are (as it should be) declared STATIC. But, all of these methods are somehow working with the database, so I need to load a model. Currently, every method has a non-static variable like this:
$comment = new Model_Comments;
$comment->addComment("abc");
OK, it seems to be working, but then I wanted to get rid of this redundancy by using class attribute to hold the instance of the model (with is class as well).
Something like this:
private static $comment; // Declaring attribute
self::$comment = new Model_Comment; // This is done within helper __constuct method
self::$comment->addComment("abc"); // And call it within the method.
But, I got failed with: Call to a member function addComment() on a non-object
Question is: is it possible to do it ? Maybe there are some other approaches ?
Sorry for a long story and, thanks in advice! :P
A static method cannot call a non-static method without operating on an instance of the class. So, what you're proposing won't work. There may be a way do accomplish something similar, but what about trying the following:
You could implement the singleton or factory pattern for your "helper" class. Then, you could create the model (as an attribute) as you instantiate/return the instance. With an actual instance of your "helper" class, you won't have to worry about the static scope issues.
In other words, you can create a helper-like class as a "normal" class in your application that, upon creation, always has the necessary model available.
I'd be happy to help further if this approach makes sense.
David