asked on

Accessing Dynamically Created Components At Runtime

I have created some tabsheets at runtime, and created ListBoxes to go with them:

// Does the Tab Exist?
TabFound := False;
if Length(TabName) > 0 then
begin
for j := 0 to PageControl1.PageCount - 1 do
begin
if PageControl1.Pages[j].Caption = TabName then
begin
TabFound := True;
Break;
end;
end;
if not TabFound then
begin
// Add Tab
with TTabSheet.Create(PageControl1) do
begin
PageControl := PageControl1;
TabVisible := True;
Caption := TabName;
// Add the ListBox
with TListBox.Create(PageControl1.Pages[PageControl1.PageCount -1]) do
begin
Parent := PageControl1.Pages[PageControl1.PageCount -1];
Top := 24;
Left := 16;
Width := 641;
Height := 297;
Name := StripSpaces(TabName)+'ListBox';
OnMouseUp := ProgramListBoxMouseUp;
end;
end;
end;
end;

I then need to access the individual list boxes to add items to them. If I use FindComponent or iterate through the component list it doesn't find any listboxes at all, not even the one created at design time:

// Load into the List Box
if TabName = '' then
ProgramListBox.Items.AddObject(DisplayText, p)
else
begin
ListBoxName := StripSpaces(TabName)+'ListBox';
// Test code to see if listboxes being found
for j := 0 to ComponentCount-1 do
begin
Temp := Components[i];
if Temp is TListBox then
ShowMessage(TListBox(Temp).Name); // This never fires, therefore no list boxes?
end;
// This should have found it and done the job!!
ListBox := TListBox(FindComponent(ListBoxName));
if ListBox <> NIL then
ListBox.Items.AddObject(DisplayText, p)
else
ShowMessage('Not Found');
end;
end;

Obviously I am missing something damn silly - anyone got any ideas?

chrisbray

ASKER

Typo in there - i instead of j:

// Load into the List Box
if TabName = '' then
ProgramListBox.Items.AddObject(DisplayText, p)
else
begin
ListBoxName := StripSpaces(TabName)+'ListBox';
// Test code to see if listboxes being found
for j := 0 to ComponentCount-1 do
begin
Temp := Components[j];
if Temp is TListBox then
ShowMessage(TListBox(Temp).Name); // This never fires, therefore no list boxes?
end;
// This should have found it and done the job!!
ListBox := TListBox(FindComponent(ListBoxName));
if ListBox <> NIL then
ListBox.Items.AddObject(DisplayText, p)
else
ShowMessage('Not Found');
end;
end;

Still doesn't work, though!!

Chris Bray.

esoftbg

Try this:

unit Unit1_Q_21485950;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ComCtrls, ExtCtrls, StdCtrls;

type
TForm1 = class(TForm)
PageControl1: TPageControl;
Panel1: TPanel;
Button1: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
{ Private declarations }
public
ListBox: TListBox;
function TabSheet_Exists(SName: string): Boolean;
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
I: Integer;
begin
with PageControl1 do
begin
for I := 0 to 9 do
begin
with TTabSheet.Create(Self) do
begin
PageControl := PageControl1;
TabVisible := (PageIndex mod 2 = 0);
Caption := 'PageIndex: ' + IntToStr(PageIndex) + ' TabIndex: ' + IntToStr(TabIndex);
Name := 'TabSheet' + IntToStr(I);
end;
end;
ListBox := TListBox.Create(Self);
ListBox.Parent := PageControl1.Pages[0];
ListBox.Height := 400;
ListBox.Width := 600;
end;
end;

function TForm1.TabSheet_Exists(SName: string): Boolean;
var
I: Integer;
begin
Result := False;
for I := 0 to ComponentCount-1 do
begin
if (Components[I] is TTabSheet) then
begin
if ((Components[I] as TTabSheet).Name=SName) then
begin
Result := True;
Break;
end;
end;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
I: Integer;
S: string;
begin
ListBox.Clear;
for I := 0 to 9 do
begin
S := 'TabSheet' + IntToStr(I);
if TabSheet_Exists(S) then
ListBox.Items.Add(S);
end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
ListBox.Free;
end;

end.

esoftbg

download above example from:
page: http://www.geocities.com/esoftbg/
link: Q_21485950.zip Accessing Dynamically Created Components At Runtime

chrisbray

ASKER

I am very sorry to say that your response is no help whatsoever... my code can already do all that and more!

The problem is after I create listboxes on the internal dynamically created pages. The reason this is a problem is that despite giving them a name which can be confirmed as given using a simple piece of test code FindComponent does not find them, and iterating through the list of components does not report ANY TListBoxes - not even the one that is created at designtime on the initial tabsheet.

Whilst I am sure that this is something stupid I am doing (or not doing) I would be very grateful to find out what it is!

To look at your example, I might need to create a listbox on TabSheet3, call it ListBox3, and add something to it. I need to be able to do ListBox3.Items.Add('ThisString') or whatever... but without pre-coding it.

Chris Bray.

chrisbray

ASKER

Here is another example that perhaps shows the problem more effectively. The following procedure is assigned to all the Listboxes as part of the creation routine in the original code:

procedure TMainForm.ProgramListBoxMouseUp(Sender: TObject;
Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
var
APoint: TPoint;
Index: Integer;
begin
if Button = mbRight then
begin
ShowMessage(TListBox(Sender).Name); // This reports the correct name of all the Listboxes

if FindComponent(TListBox(Sender).Name) <> NIL then // Returns NIL on all dynamic listboxes,
ShowMessage('Found It!') // even though sender name is correct...
else
ShowMessage('Couldn''t Find It ...');
end;
end;

As the comments show, the correct ListBox names is returned if you right click on it. However, if you call FindComponent using the correct name it returns NIL!

Chris Bray.

ASKER CERTIFIED SOLUTION

Member_2_248744

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Member_2_248744

sorry. . . I should have said -
in the
procedure TMainForm.ProgramListBoxMouseUp
code above

chrisbray

ASKER

Hi Slick812,

Thanks for that - said it was probably something stupid, didn't I? Must be going daft in my old age :-)

Chris Bray.

esoftbg

procedure TMainForm.ProgramListBoxMouseUp(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
begin
if Button = mbRight then
begin
ShowMessage(TListBox(Sender).Name); // This reports the correct name of all the Listboxes

if (Assigned(TListBox(Sender))) then
ShowMessage('Found It!')
else
ShowMessage('Couldn''t Find It ...');
end;
end;