Editing Sub-Items in List Control

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Introduction

Almost every one of us who are programming in VC++ , will come across the List control. There are many cases where there is a need to represent data in List Control in multiple columns. By default it is not possible to modify the data in the List control itself. In this small article I am putting a simple way to edit any value in any column in a Report style List control. The logic here is simple, whenever user clicks on an sub-item which he wants to modify at that place I am displaying a edit box and allowing to modify the value. Once modified and by clicking the ENTER key, the updated value is set in the List control. Here I am assuming the user is familiar with VC++ and using Class Wizard

Implementation steps:

1. Using MFC AppWizard, create a Dialog Based application. Give the application name as MultipleColumns. By default the wizard adds OK and Cancel buttons to the Dialog, Remove these two buttons.
2. Now Add a List-Control and in properties change the style to Report, this style is necessary if we want multiple columns
3. Add two buttons to the Dialog and name them as OK and Exit
4. Add one Edit box and in the properties remove the Border style
5. Using the Class Wizard add the message handlers for the OK and Exit Buttons. Add the following code to those functions

void CMultipleColumnsDlg::OK() 
{
    CDialog::EndDialog (0); // Add this line
}

void CMultipleColumnsDlg::OnExit() 
{
    CDialog::EndDialog (0); // Add this line
}

6. Add a function called InsertItems() to the CMulipleColumnsDlg class.

void InsertItems();

In the function handler add the following code

// This function inserts the default values 
// into the listControl
void CMultipleColumnsDlg::InsertItems()
{
    HWND hWnd = ::GetDlgItem(m_hWnd, IDC_LIST1);

    // Set the LVCOLUMN structure with the required 
    // column information
    LVCOLUMN list;
    list.mask =  LVCF_TEXT |LVCF_WIDTH| 
        LVCF_FMT |LVCF_SUBITEM;
    list.fmt = LVCFMT_LEFT;
    list.cx = 50;
    list.pszText   = "S.No";
    list.iSubItem = 0;
    //Inserts the column
    ::SendMessage(hWnd,LVM_INSERTCOLUMN, 
        (WPARAM)0,(WPARAM)&list);

    list.cx = 100;
    list.pszText   = "Name";
    list.iSubItem = 1;
    ::SendMessage(hWnd  ,LVM_INSERTCOLUMN, 
        (WPARAM)1,(WPARAM)&list);

    list.cx = 100;
    list.pszText   = "Address";
    list.iSubItem = 2;
    ::SendMessage(hWnd  ,LVM_INSERTCOLUMN, 
        (WPARAM)1,(WPARAM)&list);

    list.cx = 100;
    list.pszText   = "Country";
    list.iSubItem = 2;
    ::SendMessage(hWnd  ,LVM_INSERTCOLUMN, 
        (WPARAM)1,(WPARAM)&list);

    // Inserts first Row with four columns .
    SetCell(hWnd,"1",0,0);
    SetCell(hWnd,"Prabhakar",0,1);
    SetCell(hWnd,"Hyderabad",0,2);
    SetCell(hWnd,"India",0,3);

    // Inserts second Row with four columns .
    SetCell(hWnd,"2",1,0);
    SetCell(hWnd,"Uday",1,1); 
    SetCell(hWnd,"Chennai",1,2);
    SetCell(hWnd,"India",1,3);

    // Inserts third Row with four columns .
    SetCell(hWnd,"3",2,0);
    SetCell(hWnd,"Saradhi",2,1); 
    SetCell(hWnd,"Bangolore",2,2);
    SetCell(hWnd,"India",2,3);

    // Inserts fourth Row with four columns .
    SetCell(hWnd,"4",3,0);
    SetCell(hWnd,"Surya",3,1); 
    SetCell(hWnd,"Calcutta",3,2);
    SetCell(hWnd,"India",3,3);
}

7. Add another function called SetCell( ) to the CMultipleColumnsDlg class

void SetCell(HWND hWnd1, CString value, int nRow, int nCol);

In the function handler add the following code

// This function set the text in the specified 
// SubItem depending on the Row and Column values
void CMultipleColumnsDlg::SetCell(HWND hWnd1, 
        CString value, int nRow, int nCol)
{
    TCHAR     szString [256];
    wsprintf(szString,value ,0);

    //Fill the LVITEM structure with the 
    //values given as parameters.
    LVITEM lvItem;
    lvItem.mask = LVIF_TEXT;
    lvItem.iItem = nRow;
    lvItem.pszText = szString;
    lvItem.iSubItem = nCol;
    if(nCol >0)
        //set the value of listItem
        ::SendMessage(hWnd1,LVM_SETITEM, 
            (WPARAM)0,(WPARAM)&lvItem);
    else
        //Insert the value into List
        ListView_InsertItem(hWnd1,&lvItem);

}

8. Add one more function called GetItemText() to the same Class

CString GetItemText(HWND hWnd, int nItem, int nSubItem) const;

Inside the function add the following code

//this function will returns the item 
//text depending on the item and SubItem Index
CString CMultipleColumnsDlg::GetItemText(
    HWND hWnd, int nItem, int nSubItem) const
{
    LVITEM lvi;
    memset(&lvi, 0, sizeof(LVITEM));
    lvi.iSubItem = nSubItem;
    CString str;
    int nLen = 128;
    int nRes;
    do
    {
        nLen *= 2;
        lvi.cchTextMax = nLen;
        lvi.pszText = str.GetBufferSetLength(nLen);
        nRes  = (int)::SendMessage(hWnd, 
            LVM_GETITEMTEXT, (WPARAM)nItem,
            (LPARAM)&lvi);
    } while (nRes == nLen-1);
    str.ReleaseBuffer();
    return str;
}

9. Also add two member variables to the CMultipleColumnsDlg class which are of type int

int nItem, nSubItem;

10. From the Class wizard add NM_CLICK notification to the List control. Inside the function handler write the following code

//This function Displays an EditBox at the position 
//where user clicks on a particular SubItem with 
//Rectangle are equal to the SubItem, thus allows to 
//modify the value
void CMultipleColumnsDlg::OnClickList(
        NMHDR* pNMHDR, LRESULT* pResult) 
{
    Invalidate();
    HWND hWnd1 =  ::GetDlgItem (m_hWnd,IDC_LIST1);
    LPNMITEMACTIVATE temp = (LPNMITEMACTIVATE) pNMHDR;
    RECT rect;
    //get the row number
    nItem = temp->iItem;
    //get the column number
    nSubItem = temp->iSubItem;
    if(nSubItem == 0 || nSubItem == -1 || nItem == -1)
        return ;
    //Retrieve the text of the selected subItem 
    //from the list
    CString str = GetItemText(hWnd1,nItem ,
        nSubItem);

    RECT rect1,rect2;
    // this macro is used to retrieve the Rectanle 
    // of the selected SubItem
    ListView_GetSubItemRect(hWnd1,temp->iItem,
        temp->iSubItem,LVIR_BOUNDS,&rect);
    //Get the Rectange of the listControl
    ::GetWindowRect(temp->hdr.hwndFrom,&rect1);
    //Get the Rectange of the Dialog
    ::GetWindowRect(m_hWnd,&rect2);

    int x=rect1.left-rect2.left;
    int y=rect1.top-rect2.top;
    
    if(nItem != -1) 
    ::SetWindowPos(::GetDlgItem(m_hWnd,IDC_EDIT1),
        HWND_TOP,rect.left+x,rect.top+4, 
        rect.right-rect.left - 3,
        rect.bottom-rect.top -1,NULL);
    ::ShowWindow(::GetDlgItem(m_hWnd,IDC_EDIT1),SW_SHOW);
    ::SetFocus(::GetDlgItem(m_hWnd,IDC_EDIT1));
    //Draw a Rectangle around the SubItem
    ::Rectangle(::GetDC(temp->hdr.hwndFrom),
        rect.left,rect.top-1,rect.right,rect.bottom);
    //Set the listItem text in the EditBox
    ::SetWindowText(::GetDlgItem(m_hWnd,IDC_EDIT1),str);
    *pResult = 0;
}

11. To handle the ENTER key we need to write the virtual function OnOk in the MultipleColumnsDlg.h, so add the following as protected member

afx_msg void OnOK();

In MultipleColumnsDlg.cpp write the following code.

// This function handles the ENTER key 
void CMultipleColumnsDlg::OnOK() 
{   
    CWnd* pwndCtrl = GetFocus();
    // get the control ID which is 
    // presently having the focus
    int ctrl_ID = pwndCtrl->GetDlgCtrlID();
    CString str;
    switch (ctrl_ID)
    {   //if the control is the EditBox 
        case IDC_EDIT1:
        //get the text from the EditBox
        GetDlgItemText(IDC_EDIT1,str);

        //set the value in the listContorl with the
        //specified Item & SubItem values
        SetCell(::GetDlgItem (m_hWnd,IDC_LIST1),
            str,nItem,nSubItem);

        ::SendDlgItemMessage(m_hWnd,IDC_EDIT1,
            WM_KILLFOCUS,0,0);
        ::ShowWindow(::GetDlgItem(m_hWnd,IDC_EDIT1),
            SW_HIDE);
            break;     
        default:
            break;
    }
}

12. The last step in the implementation is add the following code in side the OnInitDialog function

//Set the style to listControl
ListView_SetExtendedListViewStyle(::GetDlgItem 
        (m_hWnd,IDC_LIST1),LVS_EX_FULLROWSELECT | 
        LVS_EX_GRIDLINES); 

InsertItems();
::ShowWindow(::GetDlgItem(m_hWnd,IDC_EDIT1),SW_HIDE);

Conclusion

With this I will hope , it will give an idea to edit any sub items in a List control.