Say I have two main classes, Application and ApplicationGUI. Application does lots of things and can happily run without any knowledge that ApplicationGUI exists. ApplicationGUI is linked to Application in many ways, it has maybe 50 or 100 different knobs that can change Application's behavior.
ApplicationGUI is a hierarchical structure such that it has many instances of ControlGroup, each containing an arbitrary number of Buttons and Knobs, or even another ControlGroup.
Current design: Upon instantiation of the ApplicationGUI (Application was already running with some set of default parameters), I pass pointers of Application's parameters to various components of the GUI. For example:
my_gui.sound_controlgroup.knob.link_to_param(&(my_application.volume));
If I need to do something more complex, say call a member function of Application, my_application.update_something(), how is this done?
The easy answer is to pass a pointer to my_application to my_gui.sound_controlgroup.knob, but if I only ever need to call one of my_application's functions, it seems like I am giving my knob an option to change all kinds of things that it should even know about (my_application.update_something_unrelated(), for instance). What is the cleanest thing to do in this case?
Additionally, this either requires making all subcomponents of ApplicationGUI public or having a function at each stage of the hierarchy to forward that pointer to the bottom level. This leads to quite a lot of functions. Is this a necessary consequence of a UI with a lot of knobs?
Quick Short Answer
In order to implement interaction between your non GUI related Application object and your GUIApplication object I suggest apply the "Property and Method and Event Handler" paradigm.
Extended Complex Answer
G.U.I. development is one of the most practical implementation of the O.O.P. theory.
What is the "Property and Method and Event Handler" paradigm ?
That means build, both Non GUI Classes, and GUI Classes, should have:
Properties
Methods
Event handlers
"Events" (Handlers) are also called "Signals", and are implemented with functions pointers. Not sure, but, I think your "knob" (s) are like Event Handlers.
It's a technique to apply the my_application.update_something_unrelated(), you have in your question.
Since, C++, like Java, does not have property syntax, you may use "getter" and "setter" methods, or use a "property" template.
For example, if your application has a Close method, you may declare something like the following examples.
Note: They are not full programs, just an idea:
// Applications.hpp
public class BaseApplicationClass
{
// ...
};
public class BaseApplicationClientClass
{
// ...
};
typedef
void (BaseApplicationClientClass::*CloseFunctor)
(BaseApplicationClass App);
public class ApplicationClass: public BaseApplicationClass
{
// ...
public:
Vector<BaseApplicationClientClass::CloseFunctor>
BeforeCloseEventHandlers;
Vector<BaseApplicationClientClass::CloseFunctor>
AfterCloseEventHandlers;
protected:
void ConfirmedClose();
public:
virtual void Close();
} Application;
// Applications.cpp
void ApplicationClass::ConfirmedClose()
{
// do close app. without releasing from memory yet.
} // void ApplicationClass::ConfirmedClose()
void ApplicationClass::Close()
{
// Execute all handlers in "BeforeCloseEventaHandlers"
this.ConfirmedClose();
// Execute all handlers in "AfterCloseEventaHandlers"
} // void ApplicationClass::Close()
// AppShells.cpp
public class AppShell: public BaseApplicationClientClass
{
// ...
};
void AppShell::CloseHandler(ApplicationClass App)
{
// close GUI
} // void AppShell.CloseHandler(ApplicationClass App)
void AppShell::setApp(ApplicationClass App)
{
App->BeforeCloseEventHandlers->add(&this.CloseHandler);
} // void AppShell.setApp(ApplicationClass App)
void main (...)
{
ApplicationClass* AppKernel = new ApplicationClass();
ApplicationGUIClass* AppShell = new ApplicationGUIClass();
AppShell.setApp(App);
// this executes "App->Run();"
AppShell->Run();
free AppShell();
free AppKernel();
}
UPDATE: Fixed type declaration from global function pointer (a.k.a. "global functor") to object function pointer (a.k.a. "method functor").
Cheers.
Do you know about the model-view-controller (MVC) paradigm? Think of the Application class as the model, the entire hierarchy of GUI controls as the view, and the ApplicationGUI class as the controller. You don't want Application to know about the controls, and you don't want the controls to know about Application; they should both talk only to the controller, ApplicationGUI.
Using ApplicationGUI as the conduit for communication between controls and Application means that you can test either Application or controls by replacing the other with a mock object, for example. More importantly, you can change either the controls or Application without impacting the other. Individual controls don't need to know anything about Application -- they only need to know where to send their value when it changes. And Application shouldn't care whether an input comes from a knob or a slider or a text field. Keeping those two areas separate will simplify each of them.
Additionally, this either requires making all subcomponents of
ApplicationGUI public or having a function at each stage of the
hierarchy to forward that pointer to the bottom level. This leads to
quite a lot of functions. Is this a necessary consequence of a UI with
a lot of knobs?
A given control shouldn't care what value it manages. It doesn't need to know whether the value determines the number of alien invaders on the screen or the coolant level in a nuclear reactor. It does needs to know things like the minimum and maximum values, label to display, scale to use (linear, log, etc.), and other things that directly impact the way the control works. It also needs to know who to tell when something changes, and it might need some way to identify itself.
With that in mind, ApplicationGUI doesn't need to expose accessors for every possible parameter of Application. Instead, it should have a general method that lets controls send it updates. When a control changes, it should send a message to ApplicationGUI containing the new value(s) along with its identifier, and ApplicationGUI takes care of mapping that identifier to some particular parameter of Application. A control's identifier could be some identifying number that's given to it, or it could just be a pointer to the control.
Of course, sometimes communication has to go the other way, too... a GUI usually has both inputs and outputs, so you'll want some means for ApplicationGUI to get updates from Application and update the state of the GUI. For the same reasons described above, Application should send those updates to ApplicationGUI and let the latter find the actual UI components that need to be changed.
Related
I have a Configuration that holds some basic information about file locations like download, install, picture, music, document etc. location.
These are currently exposed to QML using Q_PROPERTY. They all have their own accessors:
Q_PROPERTY(QUrl download_location READ download_location WRITE set_download_location NOTIFY download_location_changed)
These accessors basically do all the same stuff and I'd like to get rid of all this redundant code I have to write.
My first idea is to have a little nested class FileLocation that provides get, set and validation functions. But then, how would I connect these to the Q_PROPERTY?
Also, if I had something like a static functions which took parameters, (e.g. check_validity( QUrl location )), how would I hand over this parameter from QML side?
I think I'm on the wrong path here, so my question is how to keep redundant code in the context of Q_PROPERTY within reasonable limits, avoiding to write loads and loads of get, set and changed functions for very similar objects?
Here's some more code:
class Configuration : public QObject
{
QObject
Q_PROPERTY(QUrl download_location READ download_location WRITE set_download_location NOTIFY download_location_changed)
Q_PROPERTY(QUrl music_location READ music_location WRITE set_music_location NOTIFY music_location_changed)
...
signals:
void download_location_changed();
void music_location_changed();
...
public slots:
void set_download_location(QUrl location)
{
download_location = location;
emit download_location_changed(download_location);
}
void set_music_location(QUrl location)
{
music_location = location;
emit music_location_changed(music_location);
}
...
private:
QUrl download_location,
music_location,
...;
}
So as you see there's a lot of recurring code that does the same, and I'd like to damp that down a little. How do I do that? I was thinking about some general functions set, get, changed etc. that get the member to work on was a parameter. But then I didn't know how to hand over which member to work on from qml.
I just found out about the possibility to expose C++ classes to qml via qmlRegisterType(...) - maybe this is the way to go here?
You could go for an evil macro:
#define IMPL(data, name) \
inline decltype(data) name() const { return data; } \
inline void set_##name(decltype(data) value) { if (value != data) { data = value; emit name##Changed();} }
Of course, if you don't need any extra stuff, you can simply use a MEMBER property and have Qt auto generate accessors for you.
This will however not work if you need to do custom things in the accessors, the macro will, just add your stuff to it.
Lastly, when you declare a Q_PROPERTY, you can right-click the property, go to refactoring, and select "generate missing members...", Qt will generate the default stubs for the accessors, and you will only have to add your custom stuff in. The downside to this is it has the nasty habit of putting the generated code in the silliest place possible, so if you want your class to look neat, you have to move it by hand.
qmlRegisterType() is when you want to register a type so it can be created in QML, you generally don't have to do anything to access a QObject derived object from QML - it works for QObject derivatives, you only need to register a metatype for types which do not have meta information generated.
Last but not least - I don't see any point in having your configuration as a C++ object, you can just as well do it in QML, and use Qt.labs.settings to make your settings persistent. C++ is optimal for performance critical parts only. If you do your configuration in QML, you don't need to worry about any of that boilerplate code, as it is all automatic in QML, no need to write accessors, no need to recompile your project on every tiny change.
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 don't often have to create GUI's but today I do so I was hoping for some design input.
Basically I have a backend which I intend to add a GUI too using the MVC pattern. The issue is I feel whatever class encapsulates the main GUI window is going to have A LOT of state (all of the sub elements); and on top of that it's going to have a lot of setters, and possibly getter, clear, colour, size, position and refresh functions too.
One option is to march ahead with this idea and have a very large public interface which deals with the types the GUI uses (std::string, std::vector<std::string>...) the more control I want over the UI the more public member function I am going to need.
The other option would be to pass the program state to the GUI and have it decide how it display it, I fear doing this would mean it would give me less fine detail control and would break down the separation of concerns and would mean any changes to the representation of the program state would require changes in the GUI too.
Any input on the matter would be of great help.
If it makes any difference this is a C++ gui using an ncurses abstraction.
It sounds like to me you've thought alot about the M and the V, but not much about the C. The pattern should really be called MCV because the whole idea is that the controller IS the bridge between your model (data) and view (GUI). It sounds like you need a controller with most of the functionality you've mentioned.
Simply put though, your model obviously should know nothing about display and your display (view) should not know how to access the model. You need a controller that reads the data (model) and gives instructions to the display (view). If you have user interaction within the view, the controller can interpret that and modify the model as necessary.
The idea is that you never have to change all 3, but if you change the model or the view, you almost always have to update the controller.
Hope that helps...
There is at least one alternative to the giant interface. Instead of having a function that handles each thing (size, font, color, what-to-display, etc...) have a singular function that accepts a "role" and data that represents the role. This requires some sort of wrapper that can contain multiple data types.
QT's QAbstractItemModel Class Reference has a good example:
QVariant QAbstractItemModel::data ( const QModelIndex & index, int
role = Qt::DisplayRole ) const [pure virtual]
What that function will do is return the QVariant that represents the role indicated at the index provided.
The downside of this approach, is you have to know what roles exist, and what they do. QT's default roles are shown here.
I like to have parts of the model able to instrument themselves:
class Model {
private:
int value;
public:
void instrument(Instrumenter& instrumenter);
};
The Instrumenter manages the creation of controls. The model will tell it how it can be controlled and give it access to the data.
void Model::instrument(Instrumenter& instrumenter) {
instrumenter.addRangeController(0, 100, 5, value);
}
Then for different input devices (e.g keyboard, touchscreen) you can create appropriate controls:
class KeyboardInstrumenter : public Instrumenter {
public:
void addRangeController(int min, int max, int increments, int& controlled) {
// create 3 widgets, up arrow, down arrow, and value
}
};
class TouchscreenInstrumenter : public Instrumenter {
public:
void addRangeController(int min, int max, int increments, int& controlled) {
// create slider with min, max and increments
}
};
Instead of passing in the int directly we could have wrapped it in a controlling object, to aid encapsulation.
I wasn't really sure how to search for this question.
I'm doing an embedded system design with the following scenario.
I have a main application class that needs to create a bunch of hardware interfaces such as a keypad, display, communication ports, etc... a whole slew of stuff
Now I have all these objets in the main application that I can use which is great
The application class contains a few sub classes that it can go into and stay for a while. One example is a menu class that it enters and runs inside that class until the menu is closed
I need the menu class to also interact with a lot of a hardware objects that were created at the application level
What is the best way to go about this without using global variables? Is there a good solution to this problem?
I could pass each object into the menu class, but I don't want to create a constructor with 20 arguments. My current solution is to put all the objects into a structure and pass that structure into the sub-class constructor. That way they also have access.
The part that bugs me about this approach is that I have to define the structure outside of the application which I don't really like. Something just keeps telling me it's not the best solution.
Open to any suggestions.
Presumably, there is ONE keypad - thus only one "Keypad Interface Object", right? Similarly with Display [ok, there may be two displays, but still].
So my suggestion would be to have a registration and a "container" that holds the registered interfaces something like this:
class KeyPad
{
public:
int getKeyPressed();
};
class Display
{
public:
OutputText(std::string msg);
};
... bunch of other stuff ...
class HardwareRegistry
{
priviate:
Keypad *keypad;
Display *display;
static HardwareRegistry *myself;
public:
Keypad* GetKeypad() { return keypad; }
Display* GetDisplay() { return display; }
void RegisterKeypad(Keypad *akeypad) { keypad = akeypad; }
void RegisterDisplay(Display *adisplay) { display = adisplay; }
static HardwareRegistry* GetHwRegistry()
{
if (!myself) myself = new HardwareRegistry;
ASSERT(myself); // If we don't have a pointer now, panic!
return myself;
}
};
Then you just have a Singleton Pattern to provide your HardwareRegistry, and register the devices as you create them during hardware initialization.
Of course, if you support different kinds of Keypads, Displays, etc, then you would implement those with a "interface baseclass", and the registry returns the KeypadBase type, for example.
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.