So, if I had something like
class Event {// . . .}
class Children extends Event {// . . .}
class Second extends Event {// . . .}
Would there be any way to retrieve the Children and Second class objects, using the the parent class Event?
Would there be any way to retrieve the Children and Second class objects, using the parent class Event?
No. Given just the code you show, there would not be any way to identify all subclasses of Event in plain Javascript. A parent object is not informed in any way when a subclass is defined, nor is any global catalog maintained. A subclass definition stands on its own and the fact that it subclasses/extends the Event class is not saved anywhere or registered anywhere. It's just information that is used when an instance of the subclass is actually created.
If you wanted to manually keep track of such a thing, you could create your own catalog of sub-classes and then make your code register everything in that catalog.
Related
I inherited from QGraphicsItemGroup and made a class that keeps a pointer to its contained items so that I can later refer to them and change properties. It has an ellipse item and a line item and I want only the ellipse to be clickable. I need that press event of the ellipse to propagate to the QGraphicsView so that I can send a signal to some surrounding widgets.
So far I tried inheriting also from QGraphicsObject to have signals available but got stuck with ambigous base error when trying to use scene->addItem. I tried casting to QGraphicsItemGroup but I still get the error. I also tried inheriting from QObject with no success.
I'm new to QGraphics and I know the QGraphics framework has a lot of tools for user interaction and even interaction between GraphicsItems but this is really kicking my butt.
What would be the proper way to get this behavior?
Create a separate "emitter" class
To allow your subclass of QGraphicsItemGroup to emit signals, you can create a separate "emitter" class that inherits from QObject. Then, you can add an instance of this emitter class within your subclass of QGraphicsItemGroup. The emitter object can then emit signals for your subclass as needed.
QGraphicsItemGroup is treated as a single item
Unfortunately, an instance of QGraphicsItemGroup is treated as a single item, so each mousePressEvent will belong to the entire group rather than one of the members of that group (i.e., the ellipse item or the line item). If you want the mousePressEvent to behave differently depending on which item is clicked, they will need to be separate items, or you could try using line->setParentItem(ellipse) to link up the 2 items without using QGraphicsItemGroup.
I have created an derivated class from CMFCTabCtrl to have access to the ON_WM_RBUTTONDOWN message.
But it doesn't work, I think in CMainFrm I have somewhere to replace the origional class with my derivated class. But I can not find no place where the original CMFCTabCtrl class is called. So I guess that maybe happens inside another class.
By the way, EnableMDITabbedGroups is enabled.
WHAT I HAVE is a standard JavaFX application: Main.java, MainController.java & main.fxml. To add custom component, I created CustomComponentController.java and custom_component_controller.fxml.
PROBLEM is that in CustomComponentController methods I need to reference other methods and standard components from MenuController. I add public static MainController mc; to MainController class body, so that it can be seen from CustomComponentController (MainController.mc.neededMethod()). Then I try to pass everything to it in MainController.initialize() method (mc = this;) - when debugging this breakpoint, I see this full of components instances, but mc remains with null components afterwards.
QUESTION is how to reference the running instance of MainController to use its components and methods in other classes and to crossreference different custom components from each other? How to clean MainController code from event handlers and assistance methods of components by moving it all to component's own class?
I tried the following approaches, but found no way to make them work without errors:
Accessing FXML controller class
How can I access a Controller class in JavaFx 2.0?
JavaFX 2.0 + FXML. Updating scene values from a different Task
JavaFX 2.2 -fx:include - how to access parent controller from child controller
The problem can be solved if you comply the following conditions:
Not only public, but obligatory static MainController mc should be.
Do not forget id in fxml for CustomComponentController: <CustomComponentController fx:id="cc"/>, where cc is the name of the "#FXML imported" CustomComponentController in your MainController class.
Omit parameter fx:controller="main.CustomComponentController" in custom_component_controller.fxml as it results in "Controller value already specified" error (a conflict between main.fxml and custom_component_controller.fxml markup declared controllers).
Put mc = this; in the beginning of MainController's initialize() method. Before using mc in CustomComponentController class, check if it's not null. It can be null when all components, including CustomComponentController, are instantiated at application startup, but there is no mc instance yet. MainController method initialize() where MainController is instantiated is called after components are loaded. Therefore better practice is to use approach in the next paragraph.
In main.fxml create primary component of the same type that CustomComponentController and with the only fx:id parameter. Replace primary component with your CustomComponentController by creating reloadCustomComponents() method and calling it from CustomComponentController's initialize() method. Do it by adding the following to reloadCustomComponents() method:
customComponentAnchorPane.getChildren().remove(customComponent);
customComponent = new customComponent();
customComponentAnchorPane.getChildren().add(customComponent);
Thus all components can be placed outside CustomComponentController with all their methods and reloaded at the startup of the apllication. All component declarations stay in MainController class and can be reached through MainController mc reference. No duplicate creating of components in detail with parameters is needed.
Your problem looks like the classic catalog-crud forms updating, I implemented an interface that I called Updatable with an update method so I could reference any catalog form with any crud form easy after passing Controller Main Class as the UserData Property of the Child Root Component's Form
Hope it Can Solve your problem
I have a class that functions as an async TCP Client. In that class, I have a callback function, such as Client_Connected. This fires when my TCP Client has been connected. In my main viewcontroller class, I have an instance of the TCPClient and a label that I want to display the status of the tcpclient.
My question is, in the callback function of the tcpclient class, how can I reference and set the label's text in my mainviewcontroller's class?
When you create your TCPClient class, pass in a reference to your parent class (or just a reference to the label you want to update) - then your "child" class will have access to the element on the "parent" that needs to be updated.
There are probably other approaches, but this is fairly common.
I have a class which inherits from CListCtrl class, say class list.
I have another class dlg, which inherits from CDialog.
Class dlg contains an instance of class list.
I have got a delete button in class dlg, on which I delete the selected item in listCtrl and do lots of other processing.
I want the same functionality on delete key.
I added OnKeyDown() fn is my class list, where I can capture VK_DELETE key. But my problem is that, how do I do otehr processing that I need to do in dialog class.
All that processing is dlg class based not list class based.
I have many such dlg classes with different data and in every dlg class processing is different.
I tried capturing VK_DELETE in dialog class, but it doesn't capture it if focus is on list class.
I am totally stuck and have no idea, how to do this.
Please give me some idea how i can do this.
Thanks,
SG
What about delegating the call captured in the List class to the parent Dialog class. Thus you capture the VK_DELETE on the List class and say to the parent that you received a Delete command. Thus you can keep all your processing on the parent Dialog class if you wish.
((CMyParentDialog*) GetParent())->OnDeleteKeyPressed(this);
Or better, create a custom message and post it to the parent window.
#define W_DELETE_PRESSED_ON_LIST (WM_USER + 1)
GetParent()->PostMessage(WM_DELETE_PRESSED_ON_LIST);