This may seem like a trivial question, or I may have misunderstood previous information/the research I've done so far.
But is it possible to have a object with a function (in C++) that can access all instances of its own type?
In the context of my usage. I wanted to have a Button class, whereby I could simply instantiate multiple Buttons but call to a function could call reference all buttons.
ButtonInstance.isMouseTargetting(cursorCoordinates);
Is this possible? If so is it efficient?
Or should I have the class which owns the Button instances call each instance to check if the mouse coordinates match up?
I'm under the impression you are looking for advice on how to design this.
In the context of my usage. I wanted to have a Button class, whereby I
could simply instantiate multiple Buttons but call to a function could
call reference all buttons.
You want to do this in a button container. A button is not a button container and in a GUI context you already have an established hirerarchy.
Or should I have the class which owns the Button instances call each
instance to check if the mouse coordinates match up?
Yes. You probably already have a window/container class for this.
Your question is more of about Design pattern than C++ itself. Take a look at the Gang of Four book;you will find an appropriate implementation.
You can, for example, make a list of all objects created for a given class,
class Button {
public:
Button() {
_buttonList.push_back( this );
// assign index/handler to this button
}
~Button() {
_buttonList.erase( _handle );
}
static bool isMouseTargeting( float x, float y ) {
for ( auto button : _buttonList ) {
// check if inside
}
return false;
}
private:
static std::list< Button* > _buttonList;
// Handler _handle;
}
This is only a very general example of what you could do. You can use any other container besides a list (entirely up to you), and you have to find a way to index each button (or create a handle) so that you can later erase it in the destructor.
Beware of the default constructors (copy or move). If you don't explicitly create your constructors then some of your buttons will not enter the list, so either make them yourself or delete them.
Button( const Button& button ) = delete;
This is one way to do what you asked, but not necessarily the best solution. It may be simpler to just add the buttons to a non-static container by yourself and search from there.
The short answer is yes. But i will not recommend to put this functionality on the Button class since this will add extra (maybe not expected) responsibility to it. You can achieve the desired behavior by storing your Button objects on some collection and then call a function to check which button is targeted by the mouse.
Another solution would be to store the buttons collection as a member of a higher level class that represents your user-interface. This way you can call a method of this class and check if the mouse cursor is currently on some Button or not. With this design you can add the same support for other GUI elements (if you need to) easily.
Related
I'm trying to figure out the best (cleanest) way to structure some code in C++ for an application I'm building. I think MVC makes sense as the way to go, but after a fair amount of research I'm not totally clear I'm doing things the right way.
Here's an example to illustrate my question:
Model
I have a class which contains drawing data called Canvas. An example function, used to clear the current contents of the canvas, is ClearCanvas().
Ultimately, I want a button in the interface to be able to call this function and clear the canvas.
Controller
I have a controller class for the canvas: CanvasController
The controller creates and then holds a reference to a canvas object: CurrentCanvas
The controller also creates the view: CanvasView and then sets a reference to itself on the view: CurrentCanvasView->SetControllerRef(this);
View
The view is made up of a series of nested classes that define the UI. For example, the hierarchy leading to the button in question might be something like this:
CanvasView
-VerticalBox
--HorizontalBox
---Button
During the view's constructor, a reference to the controller is passed from the view to all interactive elements, eg. NewButton->SetControllerRef(this->GetControllerRef());
Button Pressed
So now when the button is pressed, it can function like this:
void ClearCanvasButton::OnButtonPressed()
{
Controller->CurrentCanvas->ClearCanvas();
}
So my general question is: (1) does this seem like the right way to be doing things, or badly structured?
Also (2): Should the controller be encapsulating the canvas functions, for example:
void CanvasController::ClearCanvas()
{
CurrentCanvas->ClearCanvas();
}
Such that the function on the button could simply be:
void ClearCanvasButton::OnButtonPressed()
{
Controller->ClearCanvas();
}
I'm just not sure whether it's correct to essentially be passing down a reference to the controller to all elements of the view which ultimately want to change the model, or whether there is a cleaner way.
Apologies if the question has been asked a thousand times in a thousand different ways, I have been searching around trying to understand this.
You don't need a class ClearCanvasButton, if your Button class contains a member like
std::function<void()> onButtonPressed;
or similar, rather than
virtual void onButtonPressed() {};
You then pass a lambda that references the controller
CanvasView::CanvasView()
{
// make the widgets
Button.onButtonPressed = [Controller](){ Controller->ClearCanvas(); };
}
In my scene I have a vector with multiple custom sprites. When I tap on one of them, I want an action to be fired on another element on the scene, can be another sprite in the vector, or another node. I have been researching the best way to do this, but I'm not quite sure how to implement it. The options are:
Add a touch listener to the scene, and verify if it was tapped inside the bounds of the sprite with rect. containsPoint(point). And after that, I have to get the sprite that was tapped to do the action I want. For me, it doesn't seems very clean to do it this way. And if two sprites are overlaped, I have to verify if the sprite is behind or in the front in order to retrieve the desired sprite. I followed this example: Touch Event example
Add a touch listener in the subclass of the sprite (my custom sprite). And add onTouchBegan and onTouchEnded inside it. But this way, I don't know how to modify an attribute of another sprite, or another element in the scene (Is it possible to use Delegates like Objective-C does?). I followed this example: Subclass Sprite Example
My main problem is that I don't understand very well how to make a node interact with another node in the scene. I have seen a lot of tutorials, but in all of them, when you interact with a node, it only changes its attributes, not other nodes' attributes.
Thanks in advance.
I shall propose "EventCustom" way :)
You can add in your touchBegan / touchEnded methods (wherever you put them... you got the point...) additional code for passing an EventCusto to the _eventDispatcher and get it announced to the world ;)
EventCustom *e = new EventCustom("MyAwesomeEvent");
e->setUserData(ptrMyFantasticData); //This function takes a void pointer. cheers :)
_eventDispatcher->dispatchEvent(e);
You may subclass the EventCustom class but that is hardly necessary. You can always hang an object to it with setUserData().
Now the objects which need to react to the event can listen to it by
_myCustomListener = EventListenerCustom::create(
"MyAwesomeEvent",
CC_CALLBACK_1(
ListeningClass::onMyAwesomeEvent,
this
)
);
_eventDispatcher->addEventListenerWithXXXXXPriority(_myCustomListener, XXX);
//ScreenGraphPriority / FixedPriority depends on situation. Either should work.
It's always a good practice to remove your listeners when you go off, so somewhere, perhaps in onExit(), where you removed touch listeners remove this listener too, as
_eventDispatcher->removeEventListener(_myCustomListener);
Going a bit off the track, a clarification:
CC_CALLBACK_X are a bit tricky names. The X indicates the no. of args the target function will get. Here, event dispatcher will pass 1 arg i.e. ptr to object of EventCustom you handed it, so we use CC_CALLBACK_1. The next arg - here "this" - is the object on which the method will be invoked.
In short, we may say that this callback is going to result into a function call this->onMyAwesomeEvent(e);
For CC_CALLBACK_2 onwards, we can specify additional args, 3rd arg onwards.
Coming back to the issue at hand, ListeningClass::onMyAwesomeEvent will look something like
void ListeningClass::onMyAwesomeEvent(EventCustom *e)
{
MyFantasticData *d = (MyFantasticData *) e->getUserData();
CCLOG("[ListeningClass::onMyAwesomeEvent] %d", d->getMyPreciousInt());
}
Hope it helps :)
Set your elements tags or names with setTag and setName. Then if element x is touched, get them with getChildByTag or getChildByName and do what you need to do.
With the second option you list above.
To make a node interact with another node in the scene you can add touch callback function to your custom sprite object like that:
https://github.com/Longpc/RTS/tree/master/Classes/base/dialogBase
and in main scene you can define function to handle this callback. So you can do every thing to unit in you scene
I have created a simple UserControl consisting solely of a Grid and an embraced Image.
Now I want to apply events such as "ManipulationDeltaEvent", etc. for touch-control. When I assign an event-handler like
pic->ActionToken = pic->ManipulationDelta +=
ref new ManipulationDeltaEventHandler(this, &MainPage::SwipeImageEventHandler);
pic->CompletedToken = pic->ManipulationCompleted +=
ref new ManipulationCompletedEventHandler(this, &MainPage::ImageManipulationCompletedEventHandler);
I receive valid EventRegistrationTokens, but when I want to swipe over the control, simply nothing happens (I debugged).
I read about overriding the OnManipulationDelta-method from Windows::UI::Xaml::Controls::Control, but I here I am stuck:
protected:
void OnManipulationDelta
(Windows::UI::Xaml::Input::ManipulationDeltaRoutedEventArgs^ e) override {
}
Although only barely related, for C++\CLI it states on MSDN:
The OnManipulationDelta method has no default implementation. Override OnManipulationDelta in a derived class to handle the ManipulationDelta event. Be sure to call the OnManipulationDelta method of the base class so that base classes receive the event.
Please give me a hint, thank you.
EDIT
The overriding is unnecessary
You need to specify ManipulationMode on the control and the control needs a non-null Background or Fill, e.g. Background="Transparent".
I have a class AwesomeMousePointer that has some function to start playing animations on the mouse:
class AwesomeMousePointer{
void startAnimat();
void stopAnimat();
};
I have another object to which I have given the responsibility of figuring out whether the mouse anims should start or not (this is based on the internal hit testing on the object, for eg: if the mouse is inside the object for a specific time)
class SomeShape(){
Event<MouseArgs> startAnim
Event<bool> interrutptAnim
bool hitTest(int x, int y);
//Inside some loop function, check if the mouse is inside the object
if(hitTest(mouseXPos, mouseYPos)){
//if the mouse if inside for x time
NotiftyEvent(startAnim, MouseArgs);
}
else{
//mouse left the object
NotifyEvent(interruptAnim, false);
}
Now, again inside my AwesomeMousePointer, I'll add listeners for the events i.e
AddListener(SomeShape::startAnim, &AwesomeMousePointer::startAnim);
AddListener(SomeShape::interruptAnim, &AweseommousePointer::interruptAnim);
The single event system by using NotifyEvent and AddListener are working correctly in short different example I tried. Now inside this application of mine, I have a lot of the objects of SomeShape and a single AwesomeMousePointer. My question is if the above logic for the anims will work or should I explicitly pass the SomeShape object explicitly to subscribe to their events, in which things would become a bit difficult.
For eg:
AddListener(shapeObject1.startAnim, &AwesomeMousePointer::startAnimat);
AddListener(shapeObject2.startAnim, &AwesomeMousePointer::startAnimat);
AddListener(shapeObject3.startAnim, &AwesomeMousePointer::startAnimat);
OR
AddListener(SomeShape::startAnim, &AwesomeMousePointer::startAnimat);
Will the second one from the above work out? If not, how will that be done without explicitly passing the object since that makes the unclear and ShapeObjects shouldn't be inside the MousePointer.
Will this work if I make the events inside SomeShape as static?
static Event<MouseArgs> startAnim
static Event<bool> interrutptAnim
You say that you don't want to have coupling between the senders and targets. In this case, usage of Poco events is not appropriate. According to http://pocoproject.org/slides/090-NotificationsEvents.pdf, you should use Notifications instead of Events, because your senders and targets do not need to know each other then.
In my application, I have my re-implemented QGraphicsView checking for a mouseReleaseEvent(), and then telling the item at the position the mouse is at to handle the event.
The QGraphicsItem for my view is made up of two other QGraphicsItems, and I check which one of the two is being clicked on (or rather having the button released on), and handle the respective events.
In my Widget's constructor, I set one of the items as selected by default, using the same methods I used when the items detect a release.
When I debugged, I found that for the LabelItem, select is called without a problem from the constructor (and the result is clear when I first start the application). But, when I click on the items, the application terminates. I saw that I was getting into the select function, but not leaving it. So the problem is here.
Which is very weird, because the select function is just a single line setter.
void LabelItem::select()
{
selected = true;
}
This is the mouseReleaseEvent;
void LayerView::mouseReleaseEvent(QMouseEvent *event)
{
LayerItem *l;
if(event->button() == Qt::LeftButton)
{
l = (LayerItem *) itemAt(event->pos());
if(l->inLabel(event->pos()))
{ //No problem upto this point, if label is clicked on
l->setSelection(true); //in setSelection, I call select() or unselect() of LabelItem,
//which is a child of LayerItem, and the problem is there.
//In the constructor for my main widget, I use setSelection
//for the bottom most LayerItem, and have no issues.
emit selected(l->getId());
}
else if(l->inCheckBox(event->pos()))
{
bool t = l->toggleCheckState();
emit toggled(l->getId(), t);
}
}
}
When I commented the line out in the function, I had no errors. I have not debugged for the other QGraphicsItem, CheckBoxItem, but the application terminates for its events as well. I think the problem might be related, so I'm concentrating on select, for now.
I have absolutely no clue as to what could have caused this and why this is happening. From my past experience, I'm pretty sure it's something simple which I'm stupidly not thinking of, but I can't figure out what.
Help would really be appreciated.
If the LabelItem is on top of the LayerItem, itemAt will most likely return the LabelItem because it is the topmost item under the mouse. Unless the LabelItem is set to not accept any mouse button with l->setAcceptedMouseButtons(0).
Try to use qgraphicsitem_cast to test the type of the item. Each derived class must redefine QGraphicsItem::type() to return a distinct value for the cast function to be able to identify the type.
You also could handle the clicks in the items themselves by redefining their QGraphicsItem::mouseReleaseEvent() method, it would remove the need for the evil cast, but you have to remove the function LayerView::mouseReleaseEvent() or at least recall the base class implementation, QGraphicsView::mouseReleaseEvent(), to allow the item(s) to receive the event.
I have seen these odd behaviours: It was mostly binary incompatibility - the c++ side looks correct, and the crash just does not make sense. As you stated: In your code the "selected" variable cannot be the cause. Do you might have changed the declaration and forgot the recompile all linked objects. Just clean and recompile all object files. Worked for me in 99% of the cases.