Limiting checked items of TCheckListBox on Delphi

checklistbox, delphi, delphi-xe, tchecklistbox

Solution

This method should do the job

procedure DoCheckListBox( AChkLb : TCheckListBox; AMaxCheck : Integer );
var
  LIdx : Integer;
  LCheckCount : Integer;
begin
  // counting
  LCheckCount := 0;
  for LIdx := 0 to AChkLb.Count - 1 do
  begin
    if AChkLb.Checked[LIdx] then
      if LCheckCount = AMaxCheck then
        AChkLb.Checked[LIdx] := False
      else
        Inc( LCheckCount );
  end;
  // enable/disable
  for LIdx := 0 to AChkLb.Count - 1 do
    AChkLb.ItemEnabled[LIdx] := AChkLb.Checked[LIdx] or ( LCheckCount < AMaxCheck );
end;

UPDATE

You better call this inside `TCheckListBox.OnClickCheck` event instead of `OnClick` event. A double-click can affect the check-state but `OnClick` is not called. `OnClickCheck` is called whenever the check-state changes.

Problem

I want to limit a TCheckListBox. I desire only 2 items should be checked, and all unchecked items will be disabled and grayed. Since the checked / unchecked items are dynamic, i can not use a static itemIndex. Here is what i tried, but i got "Out of chip bounds" error. On click event of my CheckListBox ; ``` var NumberOfCheckedItems, I: Integer; begin NumberOfCheckedItems := 0; for I := 0 to CkLst1.Count - 1 do begin if CkLst1.Checked[I] then NumberOfCheckedItems := NumberOfCheckedItems + 1; end; if NumberOfCheckedItems > 1 then begin CkLst1.Checked[I] := Enabled; CkLst1.Enabled := FALSE; CkLst1.AllowGrayed := TRUE; end else begin //no idea end; end; ```

Original source