Winapi edit controls disappear when moving window outside of the screen

Question

I'm creating several EDIT elements with a for loop. When I move the window outside the screen and then back inside, the EDIT controls disappear, along with a line in the WM_PAINT event.

The "create" event:

case WM_CREATE:
    for( int i =0; i < 4; i++ ){
        text = CreateWindow("EDIT","text",WS_VISIBLE | WS_CHILD , 0,i*40+100,100,10, hwnd , NULL, NULL, NULL);
    }

    // Other elements
    break;

The "paint" event:

case WM_PAINT:
    {
        hdc = GetDC(hwnd);
        SetRect(&secondbackground, 0, 70, 800, 500);
        FillRect(hdc, &secondbackground, CreateSolidBrush(RGB(0,200,200)) );
        ReleaseDC(hwnd, hdc);

        hdc = GetDC(hwnd);
        SetRect(&secondbackground, 0, 0, 800, 20);
        FillRect(hdc, &secondbackground, CreateSolidBrush(RGB(0,100,200)) );
        ReleaseDC(hwnd, hdc);

        hdc = BeginPaint( hwnd, &ps );
        MoveToEx(hdc,1,52,NULL);
        LineTo(hdc,100,200);
        EndPaint( hwnd, &ps );

        hdc = GetDC(hwnd);
        SetPixel(hdc,300,300,RGB(255,255,255));
        EndPaint( hwnd, &ps );
    }
    break;

Answer 1

处理WM_PAINT时使用BeginPaint / EndPaint，这将强制执行背景绘制，而GetDC则不执行。