QT learning 02 GUI program example analysis

Qt Study 02 GUI Program example analysis

GUI Program development overview

Modern operating systems support GUI Interface

• Modern operating system Provide native SDK Support GUI Application development
• GUI Application development It's on modern operating systems Mainstream technology
• On different operating systems GUI The principle of development is the same
• On different operating systems *GUI SDK Different

GUI The principle of program development

• GUI At run time, the program will Create a message queue
• The system kernel will The user action Translate into the corresponding Program messages
• The program is in Operation process China needs Real time processing of messages in the queue
• When there are no messages in the queue , The program will be in A state of stagnation

• Different operating systems Support the same GUI Principles of development

/*  Pseudo code  */
int main()
{
    
    fd = DefineMainWindow();
    win = CreateMainWindow(fd);
    CreateElements(win);
    DsiplayMainWindow(win);
    while (GetMessage(&msg)) {
    
        // Send msg to win
    }
    return 0;
}

GUI The essence of program development

GUI Application development ：

• Use... In code The program creates windows and window elements
• In message processing functions Make different responses according to program messages

classic GUI Program development mode ：

• Visual interface development , Through what you see is what you get “ draw ” Exit interface ; The development environment automatically generates the corresponding program code
• Message mapping , The program maps the specific message to the specified function ; When a message is triggered , Function called

GUI Examples of program development

• Most operating systems operate with C Function GUI SDK

• With Windows Operating system as an example

• Function name	function
  RegisterClass	Register with the system GUI Window style
  CreateWindow	Create a window or window element
  ShowWindow	Display the created window on the screen
  UpdateWindow	Refresh the window on the screen
  GetMessage	Get the message of the program message queue
  TranslateMessage	Translate system messages
  DispatchMessage	Send the message to the window handler

#include <windows.h>

#define STYLE_NAME L"MainForm"
#define BUTTON_ID 919

/*  Main window definition function  */
BOOL DefineMainWindow(HINSTANCE hInstance);
/*  Main window creation function  */
HWND CreateMainWindow(HINSTANCE hInstance, wchar_t* title);
/*  Main window internal element creation function  */
HWND CreateButton(HWND parent, int id, wchar_t* text);
/*  The main window shows functions  */
HWND DisplayMainWindow(HWND hWnd, int nCmdShow);
/*  Main window message handling function  */
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam);

static HWND MainWindow = NULL; //  The main window handle is marked 

BOOL WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    
    MSG Msg = {
    0};

    /* 1. Customize the main window style  */
    if( !DefineMainWindow(hInstance) )
    {
    
        return FALSE;
    }

    /* 2. Create main window  */
    MainWindow = CreateMainWindow(hInstance, STYLE_NAME);

    if( MainWindow )
    {
    
        /* 3. Create control elements in the main window  */
        CreateButton(MainWindow, BUTTON_ID, L"My Button");

        /* 4. Show the main window on the screen  */
        DisplayMainWindow(MainWindow, nCmdShow);
    }
    else
    {
    
        return FALSE;
    }

    /* 5. Enter the message loop  */
    while( GetMessage(&Msg, NULL, NULL, NULL) )
    {
    
        /* 6. Translate and convert system messages  */
        TranslateMessage(&Msg);
        /* 7. Distribute the message to the corresponding message processing function  */
        DispatchMessage(&Msg);
    }

    return TRUE;
}

BOOL DefineMainWindow(HINSTANCE hInstance)
{
    
    static WNDCLASS WndClass = {
    0}; //  System structure type 
                                    //  Used to describe window styles 
    WndClass.style         = 0;
    WndClass.cbClsExtra    = 0;
    WndClass.cbClsExtra    = 0;
    WndClass.hbrBackground = (HBRUSH)(COLOR_WINDOW);          //  Define the window background color 
    WndClass.hCursor       = LoadCursor(NULL, IDC_ARROW);     //  Define the mouse style 
    WndClass.hIcon         = LoadIcon(NULL, IDI_APPLICATION); //  Define the icon in the upper left corner of the window 
    WndClass.hInstance     = hInstance;                       //  Defining the window style belongs to the current application 
    WndClass.lpfnWndProc   = WndProc;                         //  Window message handling functions 
    WndClass.lpszClassName = STYLE_NAME;                      //  Window style name 
    WndClass.lpszMenuName  = NULL;

    /*  Register the defined window style into the system  */
    return RegisterClass(&WndClass);
}

HWND CreateMainWindow(HINSTANCE hInstance, wchar_t* title)
{
    
    HWND hwnd = NULL;

    hwnd = CreateWindow(STYLE_NAME,            //  Create the main window through the defined window style 
                        title,                 //  Main window title 
                        WS_OVERLAPPEDWINDOW,   //  The display style of the main window after creation 
                        CW_USEDEFAULT,         //  The upper left corner of the main window  x  coordinate 
                        CW_USEDEFAULT,         //  The upper left corner of the main window  y  coordinate 
                        CW_USEDEFAULT,         //  Main window width 
                        CW_USEDEFAULT,         //  Main window height 
                        NULL,                  //  The parent window 
                        NULL,                  //  Window menu bar 
                        hInstance,             //  The main window belongs to the current application 
                        NULL);                 //  Window parameters 

    return hwnd;

}

HWND DisplayMainWindow(HWND hWnd, int nCmdShow)
{
    
    ShowWindow(hWnd,nCmdShow); //  Display window 
    UpdateWindow(hWnd);        //  Refresh the window 

    return hWnd;
}

HWND CreateButton(HWND parent, int id, wchar_t* text)
{
    
    HINSTANCE hInstance = (HINSTANCE)GetWindowLong(parent, GWL_HINSTANCE);
    HWND hwnd = NULL;

    hwnd = CreateWindow(L"button",                               //  Create window elements through the predefined style of the system 
                        text,                                    //  Window element title 
                        WS_CHILD | WS_VISIBLE | BS_PUSHBUTTON,   //  Display style of window elements 
                        50,                                      //  The window element is in the upper left corner of the window  x  coordinate 
                        50,                                      //  The window element is in the upper left corner of the window  y  coordinate 
                        200,                                     //  The width of the window element 
                        60,                                      //  The height of the window element 
                        parent,                                  //  The parent window of the window element 
                        (HMENU)id,                               //  Window elements  ID  value 
                        hInstance,                               //  Window elements belong to the current application 
                        NULL);                                   //  Window element parameters 

	return hwnd;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    
    /*  Call the default message handling function provided by the system  */
    return DefWindowProc(hWnd, message, wParam, lParam);
}

Summary

• Modern operating system Provide native SDK Support GUI Application development

• On different operating systems GUI SDK Different

• On different operating systems GUI The principle of development is the same

• GUI Program development includes ：

  Use... In code The program creates windows and window elements

  In message processing functions Respond differently based on program messages