wxPanel 和 wxFrame 之间的交互

Question

I am trying to understand how wxFrame and wxPanel work together. I am having a hard time explaining the following code behavior:

I am trying to set up the GUI for my application. I have a function that creates a form for data entry:

void MyFrame::Initialize_Project_Info() {


//Info_Panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxSize(600, 1000), wxTAB_TRAVERSAL, _T(""));

//Info_Panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxTAB_TRAVERSAL, _T(""));

Info_Box = new wxBoxSizer(wxHORIZONTAL);
Info_Staticbox = new wxStaticBoxSizer(wxHORIZONTAL, Info_Panel, _T("Project Information"));
Info_Grid = new wxFlexGridSizer(4, 2, 0, 0);


//Note wsSize(width,height).
Project_Name = new wxStaticText(Info_Panel, wxID_ANY, _T("Project:"));
Engineer_Name = new wxStaticText(Info_Panel, wxID_ANY, _T("Engineer:"));
CrossSection_Name = new wxStaticText(Info_Panel, wxID_ANY, _T("Cross Section ID:"));
Additional_Notes = new wxStaticText(Info_Panel, wxID_ANY, _T("Additional Notes:"));


Enter_PN = new wxTextCtrl(Info_Panel, ENTER_PN, wxEmptyString, wxDefaultPosition, wxDefaultSize, wxTE_PROCESS_ENTER | wxTE_PROCESS_TAB, wxDefaultValidator, _T(""));
Enter_EN = new wxTextCtrl(Info_Panel, wxID_ANY, wxEmptyString, wxDefaultPosition, wxDefaultSize, wxTE_PROCESS_ENTER | wxTE_PROCESS_TAB, wxDefaultValidator, _T(""));
Enter_CSN = new wxTextCtrl(Info_Panel, wxID_ANY, wxEmptyString, wxDefaultPosition, wxDefaultSize, wxTE_PROCESS_ENTER | wxTE_PROCESS_TAB, wxDefaultValidator, _T(""));
Enter_AN = new wxTextCtrl(Info_Panel, wxID_ANY, wxEmptyString, wxDefaultPosition, wxSize(250, 100), wxTE_PROCESS_ENTER | wxTE_PROCESS_TAB | wxTE_MULTILINE, wxDefaultValidator, _T(""));

Info_Grid->Add(Project_Name,
    wxSizerFlags().Align(wxALIGN_LEFT | wxALIGN_CENTER_VERTICAL)
    .Border(wxTOP | wxBOTTOM | wxLEFT));
Info_Grid->Add(Enter_PN, wxSizerFlags().Expand().Border(wxALL));
Info_Grid->Add(Engineer_Name,
    wxSizerFlags().Align(wxALIGN_LEFT | wxALIGN_CENTER_VERTICAL)
    .Border(wxBOTTOM | wxLEFT));
Info_Grid->Add(Enter_EN, wxSizerFlags().Expand().Border(wxBOTTOM | wxLEFT | wxRIGHT));
Info_Grid->Add(CrossSection_Name,
    wxSizerFlags().Align(wxALIGN_LEFT | wxALIGN_CENTER_VERTICAL)
    .Border(wxBOTTOM | wxLEFT));
Info_Grid->Add(Enter_CSN,
    wxSizerFlags().Expand().Border(wxBOTTOM | wxLEFT | wxRIGHT));
Info_Grid->Add(Additional_Notes,
    wxSizerFlags().Align(wxALIGN_LEFT).Border(wxBOTTOM | wxLEFT));
Info_Grid->Add(Enter_AN, wxSizerFlags().Expand().Border(wxBOTTOM | wxLEFT | wxRIGHT));

Info_Staticbox->Add(Info_Grid);
Info_Box->Add(Info_Staticbox, wxSizerFlags().Border(wxALL));
Info_Panel->SetSizer(Info_Box);

}

This code works if I append all the objects to a wxPanel when only defined in the scope of the function. If I define the wxPanel in the scope of the constructor of the wxFrame derived class, it does not work.

For example, doing this does not generate the form as intended:

MyFrame::MyFrame() : wxFrame(NULL,wxID_ANY,"Cross Sectional Beam Properties",wxDefaultPosition,wxSize(1200,600),wxDEFAULT_FRAME_STYLE & ~(wxRESIZE_BORDER | wxMAXIMIZE_BOX)) {


Info_Panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxTAB_TRAVERSAL, _T(""));


Initialize_Project_Info();

}

So, my question is how does wxPanel interface with wxFrame. Why would one moving one line of code (ie wxPanel initialization) change the outcome?

Answer 1

From the wx docs :

A frame is a window whose size and position can (usually) be changed by the user.
It usually has thick borders and a title bar, and can optionally contain a menu bar, toolbar and status bar.

A panel is a window on which controls are placed.
It is usually placed within a frame. Its main feature over its parent class wxWindow is code for handling child windows and TAB traversal.

wxWindow is a generic class used by any type of window. wxDialog is mainly used as a form where the user enters data.

Usually an application shows a frame as the main window of the app.

==> While you can place controls directly in a wxFrame, because of 'TAB traversal' and a OS's typical background features you better use a wxPanel.

This panel is a child of the main wxFrame and you can buid it at wxFrame's ctor. Because in wxWidgets if a wxFrame has an unique child then this child is expanded to fit the whole client size of the wxFrame, then you don't use wxsizers for this panel-to-frame fitting.

When you create the controls (eg at wxPanel ctor) you set this wxPanel as the parent of the controls . And use sizers to layout them into the panel.

So each control has your panel as parent; an your panel has the frame as parent. Don't forget that 'this' pointers may be used as parents, or pass the parent as a parameter in the function that creates the windows (panel, controls).

Finally, the pointers to any wxWindow-derived class are created with "new", but you don't need to delete them, wxWigets internals takes care of their deletion.