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Failed at creating ListView in C++.

 
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Dr.Disrespect
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PostPosted: Mon Apr 10, 2017 12:39 pm    Post subject: Failed at creating ListView in C++. Reply with quote

I copied the following code from Microsoft website to create a ListView. I made some minor changes to fix compiling errors. It can be successfully compiled now, but the problem is that nothing is created, not to mention a ListView.....

PS: I did pass the handle of the main window.

Code:

HWND CreateListView(HWND hwndParent)
{
   INITCOMMONCONTROLSEX icex;           // Structure for control initialization.
   icex.dwICC = ICC_LISTVIEW_CLASSES;
   InitCommonControlsEx(&icex);

   RECT rcClient;                       // The parent window's client area.

   GetClientRect(hwndParent, &rcClient);

   // Create the list-view window in report view with label editing enabled.
   HWND hWndListView = CreateWindow(WC_LISTVIEW,
      "what",
      WS_CHILD | LVS_REPORT | LVS_EDITLABELS,
      0, 0,
      rcClient.right - rcClient.left,
      rcClient.bottom - rcClient.top,
      hwndParent,
      NULL,
      NULL,
      NULL);

   return (hWndListView);
}


And in the WinMain function, I called this:
Code:

HWND myLV = CreateListView(hwnd);  //hwnd is not NULL



But, nothing happens.

So, what did I do wrong? Sad

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atom0s
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PostPosted: Mon Apr 10, 2017 2:26 pm    Post subject: Reply with quote

Try added WS_VISIBLE to the list of flags passed to the creation.

The HMENU should have a valid ID as well and not NULL (0) since you are using WS_CHILD.

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Dr.Disrespect
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PostPosted: Mon Apr 10, 2017 3:29 pm    Post subject: Reply with quote

atom0s wrote:
Try added WS_VISIBLE to the list of flags passed to the creation.

The HMENU should have a valid ID as well and not NULL (0) since you are using WS_CHILD.


Thank you as always, atom0s. I added WS_VISIBLE, and it worked! Very Happy

With regard to "HMENU" parameter, I don't quite understand it. Is it a menu that can be defined in .rc file? I tried adding a menu and set it as the parameter, but nothing changed. Also, a menu in a ListView doesn't make sense to me neither. Can you explain a little bit?

Edit:
Actually I have two questions in the example provided by Microsoft:
Code:

HWND hWndListView = CreateWindow(WC_LISTVIEW,
                                     L"",
                                     WS_CHILD | LVS_REPORT | LVS_EDITLABELS,
                                     0, 0,
                                     rcClient.right - rcClient.left,
                                     rcClient.bottom - rcClient.top,
                                     hwndParent,
                                     (HMENU)IDM_CODE_SAMPLES,
                                     g_hInst,
                                     NULL);


The code above is used to create a ListView, I don't understand the following two parameters:
1. (HMENU)IDM_CODE_SAMPLES. I have mentioned this above.
2. g_hInst. What is this used for? "A handle to the instance of the module to be associated with the window", this explanation from MS doesn't help much. What module is it talking about?

Thanks in advance.

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atom0s
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PostPosted: Wed Apr 12, 2017 1:31 pm    Post subject: Reply with quote

With the menu HMENU param, when you use WS_CHILD that parameter becomes an identifier for the child. Not a menu id (unless specifically used as one for a child menu.)

As stated by MSDN for CreateWindow:

Code:

hMenu [in, optional]
Type: HMENU

A handle to a menu, or specifies a child-window identifier depending on the window style. For an overlapped or pop-up window, hMenu identifies the menu to be used with the window; it can be NULL if the class menu is to be used. For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.


The important part here is:
' or specifies a child-window identifier depending on the window style'
and
'For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.'

Identifiers are simply a number that is used when that child has submesssages being invoked and needs to be determined what child caused the message. For example if you have two button controls on a window, both buttons will have their own ID, such as 1000 and 10001. When you click one of the buttons WM_COMMAND will be raised and the lower word of the wParam will contain the button id to let you determine which button was pressed.

If you decide to not use ids, you will then have to sub-class the button to obtain its messages based on its hWnd instead since you will have no other way to determine which button was pressed.

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Dr.Disrespect
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PostPosted: Thu Apr 13, 2017 11:04 am    Post subject: Reply with quote

atom0s wrote:
With the menu HMENU param, when you use WS_CHILD that parameter becomes an identifier for the child. Not a menu id (unless specifically used as one for a child menu.)

As stated by MSDN for CreateWindow:

Code:

hMenu [in, optional]
Type: HMENU

A handle to a menu, or specifies a child-window identifier depending on the window style. For an overlapped or pop-up window, hMenu identifies the menu to be used with the window; it can be NULL if the class menu is to be used. For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.


The important part here is:
' or specifies a child-window identifier depending on the window style'
and
'For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.'

Identifiers are simply a number that is used when that child has submesssages being invoked and needs to be determined what child caused the message. For example if you have two button controls on a window, both buttons will have their own ID, such as 1000 and 10001. When you click one of the buttons WM_COMMAND will be raised and the lower word of the wParam will contain the button id to let you determine which button was pressed.

If you decide to not use ids, you will then have to sub-class the button to obtain its messages based on its hWnd instead since you will have no other way to determine which button was pressed.


Thanks a lot, atom0s. Very very well explained. It's good to have you around, sincerely. Smile

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