Delphi - How to delete all child components at runtime? - delphi

At design time, I create a TScrollBox which will be the parent of TLayouts created at runtime.
The Layouts will also contain Tlabels and Tedits like this:
var
Layout1: TLayout;
Label1: TLabel;
Edit1: TEdit;
begin
Layout1 := TLayout.Create(self);
Layout1.Parent := ScrollBox1;
Label1 := TLabel.Create(self);
Label1.Parent := Layout1;
Label1.Text := 'abc';
end;
Now I want to delete everything out like this procedure has never been called.
I have tried the following, but the program would just crash.
var
i : integer;
Item : TControl;
begin
for i := 0 to Scrollbox1.ControlCount - 1 do
begin
Item := Scrollbox1.controls[i];
Item.Free;
end;
end;
Can anyone please give me a hint?

When you remove a control, the index of the ones behind it in the control list shifts down. I.e, you end up trying to access positions that do not exist.
You need to iterate the list downwards:
var
i : integer;
Item : TControl;
begin
for i := (Scrollbox1.ControlCount - 1) downto 0 do
begin
Item := Scrollbox1.controls[i];
Item.Free;
end;
end;
Another way is to stay always at index 0, free its control and check that you still have controls to free:
var
i : integer;
Item : TControl;
begin
while Scrollbox1.ControlCount > 0 do
begin
Item := Scrollbox1.controls[0];
Item.Free;
end;
end;
UPDATE
As #DavidHeffernan pointed out, there is nested parentage here. This means you should free your components from bottom up. One way to do it is by recursion.
Basically you would need a procedure to encapsulate the freeing of child controls. The code would be similar to following (please note this is just a small test I did and extra code may be required):
procedure freeChildControls(myControl : TControl; freeThisControl: boolean);
var
i : integer;
Item : TControl;
begin
if Assigned(myControl) then
begin
for i := (myControl.ControlsCount - 1) downto 0 do
begin
Item := myControl.controls[i];
if assigned(item) then
freeChildControls(item, childShouldBeRemoved(item));
end;
if freeThisControl then
FreeAndNil(myControl);
end;
end;
function childShouldBeRemoved(child: TControl): boolean;
begin
//consider whatever conditions you need
//in my test I just checked for the child's name to be layout1 or label1
Result := ...;
end;
In order to free the scrollbox1 child controls (but not itself) you would call it like this:
freeChildControls(scrollbox1, false);
Please note that I had to add the childShouldBeRemoved function in order to avoid this recursive function to free child controls of the label and layout that you should leave for their destructors to free.
One possible solution to implement this function would be to use an object list where you would add your created components, and then inside the function check if the passed child component has to be freed.

If you create components at runtime - use parent control as parameter of the constructor. Like Label1 := TLabel.Create(Layout1); - so that the parent is also the owner. When you destroy Layout1 the Label1 also will be destroyed.

Related

how to retain connections between controls when copying?

i want to ask how to retain controlls when im making a copy of a control. for example i have an edit box that can be controlled with a slider for value change. when i make a copy using this code i achieve a copy of the items but the slider stops controlling editbox values. how can i fix that?
TypInfo;
procedure CloneProperties(const Source: TControl; const Dest: TControl);
var
ms: TMemoryStream;
OldName: string;
begin
OldName := Source.Name;
Source.Name := ''; // needed to avoid Name collision
try
ms := TMemoryStream.Create;
try
ms.WriteComponent(Source);
ms.Position := 0;
ms.ReadComponent(Dest);
finally
ms.Free;
end;
finally
Source.Name := OldName;
end;
end;
procedure CloneEvents(Source, Dest: TControl);
var
I: Integer;
PropList: TPropList;
begin
for I := 0 to GetPropList(Source.ClassInfo, [tkMethod], #PropList) - 1 do
SetMethodProp(Dest, PropList[I], GetMethodProp(Source, PropList[I]));
end;
procedure DuplicateChildren(const ParentSource: TWinControl;
const WithEvents: Boolean = True);
var
I: Integer;
CurrentControl, ClonedControl: TControl;
begin
for I := ParentSource.ControlCount - 1 downto 0 do
begin
CurrentControl := ParentSource.Controls[I];
ClonedControl := TControlClass(CurrentControl.ClassType).Create(CurrentControl.Owner);
ClonedControl.Parent := ParentSource;
CloneProperties(CurrentControl, ClonedControl);
ClonedControl.Name := CurrentControl.Name + '_';
if WithEvents then
CloneEvents(CurrentControl, ClonedControl);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
DuplicateChildren(Panel1);
end;
Unless I'm misunderstanding you, your CloneProperties doesn't seem to have anything to do with the question you're asking. In your example of an edit control E1 and a slider S1, you can clone both of them to produce E2 and S2, but somewhere in your code there must be a statement that changes the value in E1 depending on the value of S1. However, in the way you've most likely written it, that statement doesn't apply to E2 and S2.
The simplest way around that is to write a method which takes the component instances and links the operation of the two together. e.g.
procedure TForm1.SetEditControlFromSlider(AnEdit : TEdit; ASlider : { TWhatever the slider actually is);
begin
// Set AnEdit's value from ASlider's properties
end;
Then, you can call this with Edit/Slider pairs like this
SetEditControlFromSlider(E1, S1);
[...]
SetEditControlFromSlider(E2, S2);
I can imagine you might not like having to do that.
IMO, the cleanest solution is to avoid attempting to clone components altogether and create a TFrame containing the Edit, Slider and the code that connects them, and then add to your form as many instances of the frame as you need. It's as easy as falling off a log.
type
TEditFrame = class(TFrame) // needs to be in its own unit, Used by your form
Edit1: TEdit;
TrackBar1: TTrackBar;
procedure TrackBar1Change(Sender: TObject);
private
public
end;
[...]
procedure TEditFrame.TrackBar1Change(Sender: TObject);
begin
Edit1.Text := IntToStr(TrackBar1.Position)
end;
Then, you can add clones of the frame to TForm1 by
procedure TForm1.Button1Click(Sender: TObject);
var
AFrame : TEditFrame;
begin
Inc(FrameCount); // Field of TForm1
AFrame := TEditFrame.Create(Self);
AFrame.Name := AFrame.Name + IntToStr(FrameCount);
AFrame.Parent := Self;
AFrame.Top := AFrame.Height * FrameCount;
end;
Note that because the code which links the two components, TrackBar1Change, it compiled into the frame's unit, it is automatically shared by every instance of the frame you create, without any need to "clone" the code.

Update corresponding label depending on which combobox fired the event

I have a program with n ComboBoxes and n Labels and I want to update the corresponding Label depending on the selection from the adjacent ComboBox i.e ComboBox2 would update Label2.
I am using the same event handler for every ComboBox and currently checking if Combobox1 or Combobox2 has fired the event handler. Is there a way to use the ItemIndex of the ComboBox passed to the procedure, such as Sender.ItemIndex? This is not currently an option and gives the error 'TObject' does not contain a member named 'ItemIndex'.
procedure TForm2.ComboBoxChange(Sender: TObject);
begin
if Sender = ComboBox1 then
Label1.Caption := ComboBox1.Items.Strings[ComboBox1.ItemIndex]
else
Label2.Caption := ComboBox2.Items.Strings[ComboBox2.ItemIndex];
end;
This code has the desired behavior but is obviously not scale-able.
Every component has a Tag property inherited from TComponent, where the Tag is a pointer-sized integer. As such, you can store each TLabel pointer directly in the corresponding TComboBox.Tag, eg:
procedure TForm2.FormCreate(Sender: TObject);
begin
ComboBox1.Tag := NativeInt(Label1);
ComboBox2.Tag := NativeInt(Label2);
end;
This way, ComboBoxChange() can then directly access the TLabel of the changed TComboBox, eg:
procedure TForm2.ComboBoxChange(Sender: TObject);
var
CB: TComboBox;
begin
CB := TComboBox(Sender);
if CB.Tag <> 0 then
TLabel(CB.Tag).Caption := CB.Items.Strings[CB.ItemIndex];
end;
Option 1
This is the most robust one.
Let your form have private members
private
FControlPairs: TArray<TPair<TComboBox, TLabel>>;
procedure InitControlPairs;
and call InitControlPairs when the form is created (either in its constructor, or in its OnCreate handler):
procedure TForm1.InitControlPairs;
begin
FControlPairs :=
[
TPair<TComboBox, TLabel>.Create(ComboBox1, Label1),
TPair<TComboBox, TLabel>.Create(ComboBox2, Label2),
TPair<TComboBox, TLabel>.Create(ComboBox3, Label3)
]
end;
You need to add the controls to this array manually. That's the downside of this approach. But you only need to do this once, right here. Then everything else can be done automagically.
Now, this is where it gets really nice: Let all your comboboxes share this OnChange handler:
procedure TForm1.ComboBoxChanged(Sender: TObject);
var
i: Integer;
begin
for i := 0 to High(FControlPairs) do
if FControlPairs[i].Key = Sender then
FControlPairs[i].Value.Caption := FControlPairs[i].Key.Text;
end;
Option 2
Forget about any private fields. Now instead make sure that each pair has a unique Tag. So the first combo box and label both have Tag = 1, the second pair has Tag = 2, and so on. Then you can do simply
procedure TForm1.ComboBoxChanged(Sender: TObject);
var
TargetTag: Integer;
CB: TComboBox;
i: Integer;
begin
if Sender is TComboBox then
begin
CB := TComboBox(Sender);
TargetTag := CB.Tag;
for i := 0 to ControlCount - 1 do
if (Controls[i].Tag = TargetTag) and (Controls[i] is TLabel) then
begin
TLabel(Controls[i]).Caption := CB.Text;
Break;
end;
end;
end;
as the shared combo-box event handler. The downside here is that you must be sure that you control the Tag properties of all your controls on the form (at least with the same parent as your labels). Also, they must all have the same parent control.

Hiding items in TListBox while filtering by String

Short Version: Is there any way to control or modify LisBox items individually? for example set their Visible property to False separately.
I found a TListBoxItem class in Fire Monkey when I was searching, but I don't want to use Fire Monkey and want it in VCL.
Detailed Version:
I tried to filter my ListBox using two TStringList and an Edit, one StringList is global to keep the original list (list_files_global) and another StringList to help filtering procedure (list_files_filter) and my primary list of files is my ListBox (list_files).
I created my global StringList on onCreate event while program is starting to store my original list:
procedure Tfrm_main.FormCreate(Sender: TObject);
Begin
list_files_global := TStringList.Create;
list_files_global.Assign(list_files.Items);
End;
and used Edit's onChange event for filtering:
procedure Tfrm_main.edit_files_filterChange(Sender: TObject);
Var
list_files_filter: TStringList;
i: Integer;
Begin
list_files_filter := TStringList.Create;
list_files_filter.Assign(list_files.Items);
list_files.Clear;
for i := 0 to list_files_filter.Count - 1 do
if pos(edit_files_filter.text, list_files_filter[i]) > 0 then
list_files.Items.Add(list_files_filter[i]);
End;
and for switching off the filter, just recover the list from my global list that I created at first:
list_files.Items := list_files_global;
here so far, everything works just fine, but problem is when I'm trying to edit/rename/delete items from filtered list, for example I change an item:
list_files.Items[i] := '-- Changed Item --';
list will be edited, but when I switch off the filter, the original list will be back and all changes are lost.
so I want to know is there any proper way to solve this problem? Something like hiding items individually or change items visibility, etc... so I can change the filtering algorithm and get rid of all this making extra lists.
I searched the internet and looked into Delphi's help file for a whole day and nothing useful came up.
The items of a VCL listbox, List Box in the API, does not have any visibility property. The only option for not showing an item is to delete it.
You can use the control in virtual mode however, where there are no items at all. You decide what data to keep, what to display. That's LBS_NODATA window style in the API. In VCL, set the style property to lbVirtual.
Extremely simplified example follows.
Let's keep an array of records, one record per virtual item.
type
TListItem = record
FileName: string;
Visible: Boolean;
end;
TListItems = array of TListItem;
You can extend the fields as per your requirements. Visibility is one of the main concerns in the question, I added that. You'd probably add something that represents the original name so that you know what name have been changed, etc..
Have one array per listbox. This example contains one listbox.
var
ListItems: TListItems;
Better make it a field though, this is for demonstration only.
Required units.
uses
ioutils, types;
Some initialization at form creation. Empty the filter edit. Set listbox style accordingly. Fill up some file names. All items will be visible at startup.
procedure TForm1.FormCreate(Sender: TObject);
var
ListFiles: TStringDynArray;
i: Integer;
begin
ListFiles := ioutils.TDirectory.GetFiles(TDirectory.GetCurrentDirectory);
SetLength(ListItems, Length(ListFiles));
for i := 0 to High(ListItems) do begin
ListItems[i].FileName := ListFiles[i];
ListItems[i].Visible := True;
end;
ListBox1.Style := lbVirtual;
ListBox1.Count := Length(ListFiles);
Edit1.Text := '';
end;
In virtual mode the listbox is only interested in the Count property. That will arrange how many items will show, accordingly the scrollable area.
Here's the filter part, this is case sensitive.
procedure TForm1.Edit1Change(Sender: TObject);
var
Text: string;
Cnt: Integer;
i: Integer;
begin
Text := Edit1.Text;
if Text = '' then begin
for i := 0 to High(ListItems) do
ListItems[i].Visible := True;
Cnt := Length(ListItems);
end else begin
Cnt := 0;
for i := 0 to High(ListItems) do begin
ListItems[i].Visible := Pos(Text, ListItems[i].FileName) > 0;
if ListItems[i].Visible then
Inc(Cnt);
end;
end;
ListBox1.Count := Cnt;
end;
The special case in the edit's OnChange is that when the text is empty. Then all items will show. Otherwise code is from the question. Here we also keep the total number of visible items, so that we can update the listbox accordingly.
Now the only interesting part, listbox demands data.
procedure TForm1.ListBox1Data(Control: TWinControl; Index: Integer;
var Data: string);
var
VisibleIndex: Integer;
i: Integer;
begin
VisibleIndex := -1;
for i := 0 to High(ListItems) do begin
if ListItems[i].Visible then
Inc(VisibleIndex);
if VisibleIndex = Index then begin
Data := ListItems[i].FileName;
Break;
end;
end;
end;
What happens here is that the listbox requires an item to show providing its index. We loop through the master list counting visible items to find out which one matches that index, and supply its text.
This is something I often do, but with list views instead of list boxes. The basic principles are the same, though.
I tend to store the individual items as objects, which are reference types in Delphi. And I keep them all in one main unfiltered list, which owns the objects, while I maintain a filtered list (which does not own the objects) for display purposes. Like #Sertac, I combine this with a virtual list view.
To see how this works in practice, create a new VCL application and drop a list view (lvDisplay) and an edit control (eFilter) on the main form:
Notice I have added three columns to the list view control: "Name", "Age", and "Colour". I also make it virtual (OwnerData = True).
Now define the class for the individual data items:
type
TDogInfo = class
Name: string;
Age: Integer;
Color: string;
constructor Create(const AName: string; AAge: Integer; const AColor: string);
function Matches(const AText: string): Boolean;
end;
where
{ TDogInfo }
constructor TDogInfo.Create(const AName: string; AAge: Integer;
const AColor: string);
begin
Name := AName;
Age := AAge;
Color := AColor;
end;
function TDogInfo.Matches(const AText: string): Boolean;
begin
Result := ContainsText(Name, AText) or ContainsText(Age.ToString, AText) or
ContainsText(Color, AText);
end;
And let us create the unfiltered list of dogs:
TForm1 = class(TForm)
eFilter: TEdit;
lvDisplay: TListView;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
FList, FFilteredList: TObjectList<TDogInfo>;
public
end;
where
function GetRandomDogName: string;
const
DogNames: array[0..5] of string = ('Buster', 'Fido', 'Pluto', 'Spot', 'Bill', 'Rover');
begin
Result := DogNames[Random(Length(DogNames))];
end;
function GetRandomDogColor: string;
const
DogColors: array[0..2] of string = ('Brown', 'Grey', 'Black');
begin
Result := DogColors[Random(Length(DogColors))];
end;
procedure TForm1.FormCreate(Sender: TObject);
var
i: Integer;
begin
FList := TObjectList<TDogInfo>.Create(True); // Owns the objects
// Populate with sample data
for i := 1 to 1000 do
FList.Add(
TDogInfo.Create(GetRandomDogName, Random(15), GetRandomDogColor)
);
FFilteredList := FList;
lvDisplay.Items.Count := FFilteredList.Count;
lvDisplay.Invalidate;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
if FFilteredList <> FList then
FreeAndNil(FFilteredList);
FreeAndNil(FList);
end;
The idea is that the list view control always displays the FFilteredList, which either points to the same object instance as FList, or points to a filtered (or sorted) version of it:
// The list view's OnData event handler
procedure TForm1.lvDisplayData(Sender: TObject; Item: TListItem);
begin
if FFilteredList = nil then
Exit;
if not InRange(Item.Index, 0, FFilteredList.Count - 1) then
Exit;
Item.Caption := FFilteredList[Item.Index].Name;
Item.SubItems.Add(FFilteredList[Item.Index].Age.ToString);
Item.SubItems.Add(FFilteredList[Item.Index].Color);
end;
// The edit control's OnChange handler
procedure TForm1.eFilterChange(Sender: TObject);
var
i: Integer;
begin
if string(eFilter.Text).IsEmpty then // no filter, display all items
begin
if FFilteredList <> FList then
begin
FreeAndNil(FFilteredList);
FFilteredList := FList;
end;
end
else
begin
if (FFilteredList = nil) or (FFilteredList = FList) then
FFilteredList := TObjectList<TDogInfo>.Create(False); // doesn't own the objects
FFilteredList.Clear;
for i := 0 to FList.Count - 1 do
if FList[i].Matches(eFilter.Text) then
FFilteredList.Add(FList[i]);
end;
lvDisplay.Items.Count := FFilteredList.Count;
lvDisplay.Invalidate;
end;
The result:
Notice that there always is only one in-memory object for each dog, so if you rename a dog, the changes will reflect in the list view, filtered or not. (But don't forget to invalidate it!)

Delphi - how to address a tool in after running the program

I want to know if there is a way to address a tool which I put in my form after the program is executed? For example:
Suppose there are 100 label components in a form and you put an edit box in your form and ask the user to enter a number in the edit. When the number is written in the edit, the label with the same number will change the font colour.
But you cannot code it before running the program and need sth like this:
Label[strtoint(edit1.text)].color:=clblue;
But as you know this code does not work. What should I write to do what I want?
Yes, you can do something like you demonstrate, you just need to store the form’s controls into some type of array or list.
Sorry, I currently do not have access to my Delphi IDE, but I think I can give you an overview to what you need to do. I will also provide a link that better demonstrate the concept.
Here are the steps:
First ensure your controls have a consistent naming format that includes an index number in the name.
Example: Label1, Label2, . . . .
Next you need to store the controls into some type of an array or TList.
Example:
Var
ControlList : TList
. . . .
ControlList := TList.Create;
. . . .
{ Load the controls into the list after they been created }
ControlList.Add (Label1)
ControlList.Add (Label2)
ControlList.Add (Label3)
Here an alternatives to adding the Labels to the list manually.
for I := 1 to 3 do
begin
ControlList.Add(TLabel(FindComponent('Label'+IntToStr(I)));
end;
Now designate some event handler where you will put the code to update the label. This handler routine will first convert the user inputted value to an integer. Them use that value as an index to the control array. Once you have the label designated to be updated, set whatever properties you like.
idx := StrToInt(InputBox.Text);
lbl := TLabel( ControlList[idx])
. . . .
lbl.Color := clBlue;
Check out this link Control Arrays in Delphi for a more detailed description.
-- Update --
Although my previous answer would work, Remy Lebeau comment give me an idea to a better approach. You do not need to store the controls in an array or list, just use the Findcomponent() command to locate the control. Below are two examples demonstrating this concept.
Example using an Edit box OnKeyPress event:
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
var
LabelControl : TLabel;
begin
if ord(Key) = VK_RETURN then
begin
LabelControl := TLabel(FindComponent('Label'+Edit1.Text));
if (LabelControl <> nil) then
LabelControl.Color := clblue;
Key := #0; // prevent continue processing of the WM_CHAR message
end;
end;
Another example using a Button's OnClick event:
procedure TForm1.Button1Click(Sender: TObject);
var
LabelControl : TLabel;
begin
LabelControl := TLabel(FindComponent('Label'+Edit1.Text));
if (LabelControl <> nil) then
begin
LabelControl.Color := clBlue;
end;
end;
Things to note about the code:
In the first example, for the label to be updated, the user must press the enter key after inputting the desired label number.
In the second example, the user must press a button after entering
the number of the label to be updated.
In In both examples, invalid responses are ignored.
As I understand you right, all the Labels already contain a number in their caption.
Then, you could use the Controls array, that already exists in TForm, which contains all controls that belong to the form:
type
TForm1 = class(TForm)
Label1: TLabel;
Label2: TLabel;
Label3: TLabel;
Label4: TLabel;
// ...
Edit1: TEdit;
procedure Edit1Change(Sender: TObject);
private
public
end;
// ...
{ uses
System.RegularExpressions;
}
// ...
procedure TForm1.Edit1Change(Sender: TObject);
{
// if aLabel.Name instead of aLabel.Caption
// will work for Label1, Label2, Label3, Label4 ...
function TryNameToInt(AName: string; var ANumber: Integer): boolean;
var
aRegEx: TRegEx;
aMatch: TMatch;
aStr: string;
begin
aStr := '';
ANumber := -1;
aRegEx:= TRegEx.Create('[A-Za-z_]+([0-9]+)');
aMatch:= aRegEx.Match(AName);
if aMatch.Success then begin
aStr := aMatch.Groups.Item[1].Value;
end;
Result := TryStrToInt(aStr, ANumber);
end;}
var
aControl: TControl;
aLabel: TLabel;
aNumberEdit: Integer;
aNumberLabel: Integer;
aIdx: Integer;
begin
if TryStrToInt(Edit1.Text, aNumberEdit) then begin
for aIdx := 0 to ControlCount - 1 do begin // Controls is the list of all Controls in the form, ControlCount is the length of this list
aControl := Controls[aIdx];
if aControl is TLabel then begin // this gets only TLabel controls
aLabel := TLabel(aControl);
if TryStrToInt(aLabel.Caption, aNumberLabel)
{or TryNameToInt(aLabel.Name, aNumberLabel)} then begin
if aNumberLabel = aNumberEdit then begin
aLabel.Font.Color := clBlue;
end
else begin
aLabel.Font.Color := clWindowText; // if needed
end;
end;
end;
end;
end;
end;
You can use FindComponent function to do that:
Here I dropped a TButton and TEdit on form, you type the Label number you want to change the font color in Edit and then press the Button. Write this code in OnClick event for the Button:
Var
mColor: TColor;
mLabel: Tlabel;
begin
mColor := clGreen;
mLabel := FindComponent('Label' + Edit1.Text) as TLabel;
if mLabel <> nil then
mLabel.Font.Color := mColor;
end;
or if you don't want to press the Button and want it as you type in Edit, you have to write the code in OnChange event for Edit.

How can I refer to a control whose name is determined at runtime?

As a kind of self-study exercise, I've made a form which contains six panels in a 2x3 rectangle and I want them to switch between visible and invisible one after another. I'm trying to do so by using a for loop of some kind. I could of course write something like:
Panel1.Visible := true;
Panel1.Visible := false;
Panel2.Visible := true;
Panel2.Visible := false;
Panel3.Visible := true;
etc. etc.
But this takes quite a lot of typing and is pretty inefficient when I decide I want it to wait for 100ms between each step. For example, I'd then have to edit all the six steps to wait. This is doable for six steps, but maybe another time I want to do it a hundred times! So I'm thinking there must also be a way to use a for loop for this, where a variable varies from 1 to 6 and is used in the object identifier. So it would something like this:
for variable := 1 to 6 do begin
Panel + variable.Visible := true;
Panel + variable.Visible := false;
end;
Now, this obviously doesn't work, but I hope somebody here can tell me if this is in fact possible and if yes, how. Maybe I can use a string as the identifier? My explanation is probably pretty bad because I don't know all the technical terms but I hope the code explains something.
You can loop through the panel's Owner's Components array.
var
i: Integer;
TmpPanel: TPanel;
begin
{ This example loops through all of the components on the form, and toggles the
Visible property of each panel to the value that is opposite of what it has (IOW,
if it's True it's switched to False, if it's False it's switched to True). }
for i := 0 to ComponentCount - 1 do
if Components[i] is TPanel then
begin
TmpPanel := TPanel(Components[i]);
TmpPanel.Visible := not TmpPanel.Visible; // Toggles between true and false
end;
end;
You can also use the FindComponent method, if you want a very specific type of component by name. For instance, if you have the 6 panels, and their names are Panel1, Panel2, and so forth:
var
i: Integer;
TmpPanel: TPanel;
begin
for i := 1 to 6 do
begin
TmpPanel := FindComponent('Panel' + IntToStr(i)) as TPanel;
if TmpPanel <> nil then // We found it
TmpPanel.Visible := not TmpPanel.Visible;
end;
end;
This is a situation where you want to create the controls dynamically at runtime rather than at designtime. Trying to grapple with 6 different variables is just going to be a world of pain. And when you need the grid to be 3x4 rather than 2x3, you'll regret that decision even more.
So, start with a completely blank form. And add, in the code, a two dimensional array of panels:
private
FPanels: array of array of TPanel;
Then, in the form's constructor, or an OnCreate event handler, you can initialise the array by calling a function like this:
procedure TMyForm.InitialisePanels(RowCount, ColCount: Integer);
var
Row, Col: Integer;
aLeft, aTop, aWidth, aHeight: Integer;
Panel: TPanel;
begin
SetLength(FPanels, RowCount, ColCount);
aTop := 0;
for Row := 0 to RowCount-1 do begin
aLeft := 0;
aHeight := (ClientHeight-aTop) div (RowCount-Row);
for Col := 0 to ColCount-1 do begin
Panel := TPanel.Create(Self);
FPanels[Row, Col] := Panel;
Panel.Parent := Self;
aWidth := (ClientWidth-aLeft) div (ColCount-Col);
Panel.SetBounds(aLeft, aTop, aWidth, aHeight);
inc(aLeft, aWidth);
end;
inc(aTop, aHeight);
end;
end;
And now you can refer to your panels using cartesian coordinates rather than a flat one dimensional array. Of course, you can easily enough declare a flat one dimensional array as well if you want.
The key idea is that when you are creating large numbers of control in a structured layout, you are best abandoning the designer and using code (loops and arrays).
Use FindComponent method of TComponent:
for variable := 1 to 6 do begin
pnl := FindComponent('Panel' + IntToStr(variable));
if pnl is TPanel then
begin
TPanel(pnl).Visible := true;
TPanel(pnl).Visible := false;
end;
end;
As others have answered, FindComponent is the way to go.
But if you just want to modify generic properties for the component, such as visible, position etc, it's not necessary to compare to the type.
This will work just as fine:
for i := 1 to 16 do
begin
(FindComponent( 'P' + inttostr(i) ) as TControl).Visible := false;
end;
(NOTE: this is for Delphi 6/ 7, modern versions probably do this in other ways)
Actually my answer
If you use a name convention to name your component like
"Mycomponent" + inttostr(global_int)
you can use it to find it very easily :
function getMyComponent(id:integer) : TComponent;
begin
result := {Owner.}FindConponent('MyComponent'+inttostr(id));
end;
You also can make your generated components to interact each other by using (sender as TComponent).name to know which other component are related to him.
Exemple
Following is an example of what you can do with this :
Imagine a pagecontrol where tabs are an interface you want to have multiple time
(for ex, to describe columns in a file with 1 tab = 1 col, and you want to dynamically add tabs).
For our example, we are naming button and edit this way :
Button : "C_(column_number)_btn"
Edit : "C_(column_number)_edi"
You can actually refer directly to the edit with a buttonclick, linked at runtime by calling findcomponent :
procedure TForm1.ColBtnClick(Sender:TObject);
var nr : string; Edit : TEdit;
begin
// Name of the TButton. C(col)_btn
nr := (Sender as TButton).Name;
// Name of the TEdit C_(column)_edi
nr := copy(nr,1,length(nr)-3)+'edi';
// Get the edit component.
edit := (Form1.Findcomponent(nr) as TEdit);
//play with it
Edit.Enabled := Not Edit.Enabled ;
showmessage(Edit.Text);
Edit.hint := 'this hint have been set by clicking on the button';
//...
end;
Of course, you link this procedure to every generated buttons.
If anyone wants to practice with it, you may want to know how to generate the tabsheet and components, here you go :
procedure Form1.addCol(idcol:integer, owner : TComponent); // Form1 is a great owner imo
var
pan : TPanel; // Will be align client with the new tabsheet
c: TComponent; //used to create components on the pannel
tab : TTabSheet;
begin
try
pan := TPanel.create(owner);
pan.name := format('Panel_%d',[idcol]);
pan.caption := '';
// dynamically create that button
c := TButton.create(Owner);
with c as TButton do
begin
Name := format('C%d_btn',[idcol]);
Parent := pan;
//Top := foo;
//Left := bar;
caption := 'press me';
OnClick := Form1.ColBtnClick; // <<<<<<< link procedure to event
end;
//create a Tedit the same way
c := TEdit.create(Owner);
with c as TEdit do
Name := format('C%d_edi',[idcol]);
Parent := pan;
// other properties
// create the tabsheet and put the panel in
finally
tab := TTabSheet.Create(Parent);
tab.caption := 'Column %d';
tab.PageControl := Pagecontrol1;
pan.Parent := tab;
pan.Align := alClient;
end;
end;
Generating names to get the component is actually a very good way to have a clean code.
Scrolling through parent - child components in order to find the one you want is actually inefficient and becomes hell if there is many component (in my example, if there is 3, 10 or unknown number of TEdit looping child (brother) components will be ugly.
Maybe this example is useless but It may helps someone, someday.

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