I have a custom control which needs to get access to the height of the main form it is on. Since it is common for this control to be nested in a series of panels, I have written this code to try and get me to the main form:
TControl * control = this;
while( control->HasParent() )
{
control = control->ParentControl;
ShowMessage( control->Name );
}
Using the ShowMessage statement to track my progress, as I step through the code I get all the way up to "BasePanel" which in this case is the last control up the ladder before the "MainForm." However, when the call to ShowMessage happens for what should be the "MainForm" I get an access violation.
Is there some reason I am unable to access the main form of a control this way? Is there a better way to access a control's main form?
You are not checking if ParentControl returns a NULL pointer before reading its Name. When HasParent() returns true, ParentControl is NOT guaranteed to be valid. Case in point - TForm is NOT a TControl descendant in FireMonkey, so it cannot be returned by ParentControl.
The purpose of HasParent() is to report whether the component has a parent or not. TFmxObject overrides HasParent() to report whether the TFmxObject.Parent property is NULL, and overrides GetParentComponent() to return an appropriate TComponent for that parent. TFmxObject.Parent returns a TFmxObject, as parent/child relationships do not have to be visual in FireMonkey like they do in VCL, so Parent and GetParentComponent() can actually return different objects at times.
You should be using GetParentComponent() instead of ParentControl, as the documentation says:
Call HasParent to determine whether a specific component has a parent.
Derived classes override this method to implement proper handling for parenting.
Use GetParentComponent to retrieve the component reference.
For example:
TComponent * comp = this;
while( comp->HasParent() )
{
comp = comp->GetParentComponent();
ShowMessage( comp->Name );
}
However, if your intent is to find the parent TForm specifically, use your control's Root property instead:
TCommonCustomForm *form = dynamic_cast<TCommonCustomForm*>(this->Root->GetObject());
Related
In gtkmm 4, how can one get the X Window ID of type XID as defined in X11/X.h, from inside a class, that inherits from Gtk::Widget?
Not all of them have one.
Those widgets that do will implement the GtkNative interface, which provides the gtk_native_get_surface function, allowing you to obtain a GdkSurface. In gtkmm, this will correspond to casting to to Gtk::Native and calling get_surface.
To obtain a Window handle from that, you can use the GDK_SURFACE_XID macro. For that, I don’t think a C++ wrapper exists; you will have to call Gdk::Surface::gobj to obtain a GdkSurface * and use the C API.
I wanted to add two things to the accepted answer
It is of course important to check if get_surface() returned a valid nonzero object indeed. Otherwise get the ID after the Widget's signal_realize() is emitted, which is done after the widget is assigned to a surface. This can be achieved by overriding the default handler on_realize()
Instead of casting and calling ((Gtk::Native)this)->get_surface() it is also possible to call like get_native()->get_surface().
In conclusion do
void myWidget::on_realize() {
// Call default handler
Gtk::Widget::on_realize();
XID x_window = GDK_SURFACE_XID(get_native()->get_surface()->gobj());
}
to get the X window ID as early as possible.
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'd like to understand how to do a specific task. I was trying to set up event tables in wxWidgets and ran into an issue with their behaviour.
I set up some code in one class:
void TopRightPanel::OnSelChanged(wxTreeEvent& event)
{
wxTreeItemId item = event.GetItem();
TreeItemData* data = (TreeItemData *) GetItemData(item);
if(data != NULL)
{
particleSystemManager->SetSelectedParticleSystem(data->particleSystem);
}
}
This works fine and has the right values as expected. My problem with this though is that it's self contained and I want the class above it in the hierarchy to read the treeCtrl's action and make changes to all aspects of the U.I. So I tried this:
void Window::OnSelChanged(wxTreeEvent& event)
{
wxTreeItemId item = event.GetItem();
TreeItemData* data = (TreeItemData *) topRightPanel->GetItemData(item);//item.m_pItem.//m_MyTreeCtrl->GetItemData(itemId);*/
if(data != NULL)
{
particleSystemManager.SetSelectedParticleSystem(data->particleSystem);
}
}
Now I get an unhandled exception when topRightPanel->GetItemData(data) is called. The topRightPanel it uses doesn't seem to be updated and seems to be pointing to data before it's enstantuated in the class' constructor. Is there anyway I can get round this?
Edit:
I declare the event table like so:
#if USE_GENERIC_TREECTRL
BEGIN_EVENT_TABLE(TopRightPanel, wxGenericTreeCtrl)
#else
BEGIN_EVENT_TABLE(TopRightPanel, wxTreeCtrl)
#endif
EVT_TREE_SEL_CHANGED(TopRightPanel_Ctrl, Window::OnSelChanged)
END_EVENT_TABLE()
and I then declare the table in the header using DECLARE_EVENT_TABLE.
You must use the same class name in the event table macros that you used in BEGIN_EVENT_TABLE. IOW, your handler must be defined in Window event table and not in TopRightPanel event table. As tree events are wxCommandEvents, they are propagated upwards to the parent so if Window contains the tree control, this will work. Otherwise, e.g. if they are siblings, you would have to use Connect() as indicated in another answer.
(Re)reading the event handling overview would be highly recommended.
You don't show how do you connect this event handler but the problem is almost surely there and not in the code you show. If you're using Connect(), make sure that you pass the pointer to Window object as its last argument, otherwise you end up calling a method of Window class on TopRightPanel object with the unsurprisingly catastrophic consequences.
If you're sure that you do call the method on the right object, then the only other explanation I see is that you don't initialize topRightPanel before the first event of this type is generated. If this is the case, the simplest solution is to initialize the pointer to NULL and set it correctly at the end of the initialization code. And, of course, check for the pointer being non-NULL in the event handler.
Is it possible to simply indicate the change of some Qt control's property by changing value of user defined variable (perform an action on changing value). Eg. I declared int a which is frequently used by multiple functions. Now I need to construct a relation: if ( a == 0 ) then my control is inactive else my control is active. (I was inspired by C# data bindings.)
In Qt, controls are enabled/disabled with QWidget::setEnabled. What you'll need to do is create a subclass from which all your gui windows are derived, in which you define a function that sets this variable and calls setEnabled. Like this:
class Widget : public QWidget
{
...
MySetEnabled(bool b)
{
a = b;
setEnabled(b);
}
int a;
};
Signals/Slots
In your accessor methods emit a signal that connect to actions you like to happen.
For example, in an MFC program, I have my main application and a 'class'. What should I do if I want to update a control (say, a listbox) that is situated on my main application from that 'class'?
heres an example that worked for me
theApp.m_pMainWnd->GetDlgItem(IDC_BUTTON6)->SetWindowTextW(L"Run Auto Test");
Your class can be designed to trigger an event which your main application can listen for. Then, a listener/event handler/delegate can be called to handle the event and update the listbox. Typically, most event formats pass a reference of the sender, in this case your 'class', as well as an object containing event arguments. These arguments can be used to pass the list of items you want to add to your listbox.
If you have the handle to dialog object in your class, then you can use GetDlgItem(ResourceID) to get list control object.
The easiest approach is to expose the listview from your application form/window to the classes that use it. You can do this either by passing the listview object (or parent window) to the class constructor, or storing it in a static variable that is accessible by the class.
For better encapsulation, you can put a method in the application that the class can call, e.g. "AddItemToListBox()". This allows the application object to remain in control of how you access the listbox. Again you can do this as a static method, or pass the main program object's 'this' pointer into the class constructor.
i.e.
class CApplication
{
CListBox m_ListBox;
public:
static void CApplication::AddItemToListBox(CString itemText)
{
// Add the item as you wish here
}
}
class CMyClass
{
afx_msg void CMyClass::OnMouseDown(...)
{
CApplication::AddItemToListBox("This is a test");
}
}