Knowledge Base

PRB: Delete All Columns in the List Control

Article ID: 198232

Article Last Modified on 12/11/2003

APPLIES TO

This article was previously published under Q198232

SYMPTOMS

When you attempt to delete columns from the List control, you might receive unexpected results. In particular, trying to delete all the columns in the List control might not work.

CAUSE

Because of the internal design of the List control, this problem can occur when you delete all the columns from a List control through a forward iterating loop. For example, when you delete the column at index 0, Column(0), the indices of all of the remaining columns decrement by one (for example, Column(1) becomes Column(0)).

The following sample code does not delete all of the columns: 
   CListCtrl *m_pList = NULL;
   m_pList = (CListCtrl*) GetDlgItem(IDC_LIST1);
   int nColumns = 10;
   for ( int i = 0; i < nColumns; i++)

     m_pList->DeleteColumn (i);
In the first pass of the loop, Column(0) is deleted and all the column indices decrement by one. As a result, Column(1) becomes Column(0) in the first pass of the loop. In the second pass of loop, the value of i is 1, so Column(1) is deleted and the loop never gets to Column(0).

RESOLUTION

If you want to delete all the columns in a loop, you need to delete the columns in the reverse order in which they were added. So you need to have a decrementing loop instead of an incrementing loop. If the total number of columns is ten (0-9) in the List control, you need to start deleting from the last column, Column(9), instead of the first, Column(0), as in the following example: 
   CListCtrl *m_pList = NULL;
   m_pList = (CListCtrl*) GetDlgItem(IDC_LIST1);
   int nColumns = 10;
   for ( int i = nColumns-1; i >= 0; i--)
     m_pList->DeleteColumn (i);

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Add and Delete All Columns from the List Control

  1. Open Visual C++. Click New on the File menu and select MFC AppWizard in the Projects tab.
  2. Type ListCtrlTest in the Project name box and click OK.
  3. In the next step, Step 1, select Dialog based for "What type of application would you like to create?" and click Finish. Click OK on the New Project Information dialog box.
  4. Add a command button to your dialog box from the Controls bar. Right-click on the command button and then click Properties. Change the Caption of the command button to CreateColumns and change the ID to IDC_CREATECOLUMNS. Close the Properties dialog box.
  5. Add another command button. Use the Properties dialog box to change the Caption to DeleteAllColumns and change the ID to IDC_DELETEALLCOLUMNS.
  6. Add a List control to your dialog box from the Controls bar. Open the Properties dialog box. Click the Styles tab and change the View to Report. Close the Properties dialog box.
  7. Press the CTRL key and double-click the List control to add the member variable for it. Type m_listctrl in the Member variable name box and click OK.
  8. Double-click the CreateColumns command button to add a command handler to it. Click OK to open the code window and place the following code in the CListCtrlTestDlg::Oncreatecolumns() function: 
          CString str;
      for (int i = 0; i>10; i++) // Insert ten columns.
      {
         str.Format("Column#: %d", i);
         m_listctrl.InsertColumn(i, str, LVCFMT_LEFT, 75);

      }
  9. Double-click the DeleteAllColumns command button to add a command handler to it. Place the following code in the CListCtrlTestDlg::OnDeleteallcolumns() function: 
          // Delete all the columns in descending order.
      for ( int i = 9; i >=0; i--)
         m_listctrl.DeleteColumn(i);
  10. Save, compile, and run your code.

REFERENCES

LISTHDR MFC sample in VC++ Help.

CListCtrl documentation in MSDN.

Additional query words: MFC Listview CListCtrl

Keywords: kbprb kbctrl kbcode KB198232


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