TCustomListBox.ItemAtPos Method

Returns the index of the list box item indicated by the coordinates of a point on the control.

Pascal

function ItemAtPos(Pos: TPoint; Existing: Boolean): Integer;

C++

__fastcall int ItemAtPos(TPoint Pos, Boolean Existing);

Description

Use ItemAtPos to detect if an item exists at a particular point in the control.

The Pos parameter is the point in the control in window coordinates. If Pos is beyond the last item in the list box, the value of the Existing variable determines the returned value. If Existing is set to true, ItemAtPos returns -1, indicating that no item exists at that point. If Existing is set to false, ItemAtPos returns the index of the last item in the list box plus one.

C++ Examples:

Copy Code

/*
For the following example, add a button, a status bar, and a
list box to the form. Set the SimplePanel property of the
status bar to true, using the object inspector. Also, populate
the OnMouseUp event handler for the list box.  The following
code fills a list box with the names of all components on the
form when the user clicks the button. References to the
components themselves are inserted along with the names. The
components are all inserted at the front of the list, so that
the last component added to the form is the first component
in the list.  When the user right-clicks the name of an
object in the list, the component’s coordinates are displayed
on the status bar. Note that because we are using the right-
click, the item need not be selected.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  for (int i = 0; i < ComponentCount; i++)
    ListBox1->Items->InsertObject(0,
                                  Components[i]->Name, 
                                  dynamic_cast<TObject *>(Components[i]));
}

void __fastcall TForm1::ListBox1MouseUp(TObject *Sender, TMouseButton Button,
      TShiftState Shift, int X, int Y)
{
  if (Button == mbRight)
  {
    TClass ClassRef;
    int Index = ListBox1->ItemAtPos(Point(X,Y), true);
    // only components that are controls have a position
    // make sure the component is a control
    for (ClassRef = ListBox1->Items->Objects[Index]->ClassType();
         ClassRef != NULL;
         ClassRef = ClassRef->ClassParent())
      if (String(ClassRef->ClassName()) == "TControl")
      {
        TControl *TheObject = dynamic_cast<TControl *>(ListBox1->Items->Objects[Index]);
        StatusBar1->SimpleText =
          TheObject->Name + " is at (" +
          IntToStr(TheObject->Left) + ", " +
          IntToStr(TheObject->Top) + ")";
         break;
      }
    if (ClassRef == NULL) // if it wasn't a control
      MessageBeep(0);
  }
}

Delphi Examples:

Copy Code

{
For the following example, add a button, a status bar, and a
list box to the form. Set the SimplePanel property of the
status bar to true, using the object inspector. Also, populate
the OnMouseUp event handler for the list box.  The following
code fills a list box with the names of all components on the
form when the user clicks the button. References to the
components themselves are inserted along with the names. The
components are all inserted at the front of the list, so that
the last component added to the form is the first component
in the list.  When the user right-clicks the name of an
object in the list, the component’s coordinates are displayed
on the status bar. Note that because we are using the right-
click, the item need not be selected.
}
procedure TForm1.Button1Click(Sender: TObject);
var
  I: Integer;
begin
  for I := 0 to Form1.ComponentCount-1 do
    ListBox1.Items.InsertObject(
      0, Form1.Components[I].Name, 
      Form1.Components[I] as TObject);
end;

procedure TForm1.ListBox1MouseUp(
  Sender: TObject; Button: TMouseButton; 
  Shift: TShiftState; X,Y: integer);
var
  APoint: TPoint;
  Index: integer;
  TheObject: TControl;
begin
  if Button = mbRight then
  begin
  APoint.X := X;
  APoint.Y := Y;
  Index := ListBox1.ItemAtPos(APoint, True);
  if (ListBox1.Items.Objects[Index] is TControl) then 
  begin
    TheObject := 
      (ListBox1.Items.Objects[Index] as TControl);
    StatusBar1.SimpleText := TheObject.Name + ' is at (' +
                           IntToStr(TheObject.Left) + ', ' +
                           IntToStr(TheObject.Top) + ') ';
  end
  else
    Beep;
  end;
end;