Title: Which column was clicked in a TListView?
Question: How can I know which column was click in a TListView? GetItemAt only works with the first column.
Answer:
The method GetItemAt only provides the information about which
ListItem (if any) is located at the specified coordinates passed as
parameters, but only works with the first column of the TListView.
The rest are ignored. If we needed to know if the user clicked on an
element in another column, we can declare a new method in a derived
class:
type
TListViewX = class(TListView)
public
function GetItemAtX(X, Y: integer; var Col: integer): TListItem;
end;
implementation
function TListViewX.GetItemAtX(X, Y: integer;
var Col: integer): TListItem;
var
i, n, RelativeX, ColStartX: Integer;
ListItem: TlistItem;
begin
Result := GetItemAt(X, Y);
if Result nil then begin
Col := 0; // First column
end else if (ViewStyle = vsReport)
and (TopItem nil) then begin
// First, let's try to find the row
ListItem := GetItemAt(TopItem.Position.X, Y);
if ListItem nil then begin
// Now let's try to find the Column
RelativeX := X-ListItem.Position.X-BorderWidth;
ColStartX := Columns[0].Width;
n := Columns.Count - 1;
for i := 1 to n do begin
if RelativeX if RelativeX StringWidth(ListItem.SubItems[i-1]) then
begin
Result := ListItem;
Col := i;
break;
end; //if
Inc(ColStartX, Columns[i].Width);
end; //for
end; //if
end; //if
end;
Casting to the new class
------------------------
We don't need to intall this new component and register it in the
components palette as we explained in another article ("Adding new
methods and properties without registering new components"). Instead,
any time we want to access this method, we can just cast the object
(for example ListView1) to our new class. For example in a MouseDown
event:
procedure TForm1.ListView1MouseDown(Sender: TObject;
Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
col: integer;
li: TListItem;
begin
li := TListViewX.GetItemAtX(x, y, col);
if li nil then
ShowMessage('Column #' + IntToStr(col));
end;