How to put controls into a Design State Mode just like the Form Designer does?

Question

This one has been puzzling me for some time now and maybe the answer is an easy one, or perhaps it involves much more VCL hacking or magic to accomplish what I am looking for but either way I am at a loss as to how to solve my problem.

If you look at the Delphi Form Designer you will see that none of the controls animate when the mouse moves over them, they also cannot receive focus or input (eg you cannot type into a TEdit, click a TCheckBox or move a TScrollBar etc), only at runtime do the controls behave normally and respond to user interaction.

I want to know how can I implement this type of behavior to any control at runtime, eg set controls into like a Designer State Mode? However, controls should also still respond to Mouse Events such as OnMouseDown, OnMouseMove, OnMouseUp etc so they can be moved and sized if needed for example.

This is the closest that I managed:

procedure SetControlState(Control: TWinControl; Active: Boolean);
begin
  SendMessage(Control.Handle, WM_SETREDRAW, Ord(Active), 0);
  InvalidateRect(Control.Handle, nil, True);
end;

Which could be called simply like so:

procedure TForm1.chkActiveClick(Sender: TObject);
begin
  SetControlState(Button1, chkActive.Checked);
  SetControlState(Button2, chkActive.Checked);
  SetControlState(Edit1, chkActive.Checked);
end;

Or for example, all controls on the form:

procedure TForm1.chkActiveClick(Sender: TObject);
var
  I: Integer;
  Ctrl: TWinControl;
begin
  for I := 0 to Form1.ControlCount -1 do
  begin
    if Form1.Controls[I] is TWinControl then
    begin
      Ctrl := TWinControl(Form1.Controls[I]);
      if (Ctrl <> nil) and not (Ctrl = chkActive) then
      begin
        SetControlState(Ctrl, chkActive.Checked);
      end;
    end;
  end;
end;

Two problems I have noticed with the above is that whilst the controls do appear to become Design State like, some controls such as TButton still have the animation effect painted on them. The other issue is when pressing the left Alt key when the controls are Design State like causes them to disappear.

So my question is, how do I put controls into a Design State mode at runtime just like the Delphi Form Designer does, where those controls do not animate (based on Windows Theme) and cannot receive focus or input?

To make that bit clearer, look at this sample image based off the above code sample where the controls are no longer active, but the TButton's animation paint is still active:

But should actually be:

From the two images above, only the TCheckBox control can be interacted with.

Is there a procedure hidden away somewhere that can change the state of a control? Or perhaps a more suitable approach to achieving this? The code I managed to get so far just presents more problems.

Setting the controls to Enabled := False is not an answer I am looking for either, yes the behavior is kind of the same but of course the controls paint differently to show they are disabled which is not what I am looking for.

Answer 1

What you are looking for is not a feature of the controls themselves, but rather is an implementation of the Form Designer itself. At design-time, user input is intercepted before it can be processed by any given control. The VCL defines a CM_DESIGNHITTEST message to allow each control to specify whether it wants to receive user input at design-time (for example to allow visual resizing of list/grid column headers). It is an opt-in feature.

What you can do, though, is put the desired controls onto a borderless TPanel, and then simply enable/disable the TPanel itself as needed. That will effectively enable/disable all user input and animations for its child controls. Also, when the TPanel is disabled, the child controls will not render themselves as looking disabled.

Answer 2

Remy Lebeau's answer on putting controls into a container such as a TPanel, and then setting the panel to Enabled := False does put the controls into the state I was looking for. I also discovered that overriding the controls WM_HITTEST put the controls into the same state, eg they don't receive focus and cannot be interacted with. The problem with those two is that the controls still need to be able to respond to MouseDown, MouseMove and MouseUp events etc but they no longer cannot.

Remy also suggested writing a class and implement Vcl.Forms.IDesignerHook, something I have not attempted yet as maybe it requires too much work for what I need.

Anyway, after lots of playing around I found another alternative way, it involves the use of PaintTo to draw the control onto a canvas. The steps I did are as follows:

• Create a custom TPanel with an exposed Canvas
• At FormCreate create and align the custom panel to client
• Add controls to the form at runtime (bringing the custom panel to the front)
• Call the controls PaintTo method onto the custom panels Canvas

What this is essentially doing is creating the components and using the Form as the parent with our custom panel sitting on top. The controls are then painted onto the panels canvas which makes it appear as if the control is on the panel, when actually it sits underneath on the form undisturbed.

Because the controls are underneath the panel, in order for them to respond to events such as MouseDown, MouseMove and MouseUp etc I overrided the WM_NCHitTest in the panel and set the result to HTTRANSPARENT.

In code it would look something like this:

Custom panel:

type
  TMyPanel = class(TPanel)
  protected
     procedure WMNCHitTest(var Message: TWMNCHitTest); message WM_NCHitTest;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;

    property Canvas;
  end;

{ TMyPanel }

constructor TMyPanel.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);

  Align := alClient;
  BorderStyle := bsNone;
  Caption := '';
end;

destructor TMyPanel.Destroy;
begin
  inherited Destroy;
end;

procedure TMyPanel.WMNCHitTest(var Message: TWMNCHitTest);
begin
  Message.Result := HTTRANSPARENT;
end;

Form:

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FMyPanel: TMyPanel;
    procedure ControlMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  public
    { Public declarations }
  end;

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  FMyPanel := TMyPanel.Create(nil);
  FMyPanel.Parent := Form1;
end;

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

procedure TForm1.ControlMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Sender is TWinControl then
  begin
    ShowMessage('You clicked: ' + TWinControl(Sender).Name);
  end;
end;

Example of adding a TButton to the form:

procedure TForm1.Button1Click(Sender: TObject);
var
  Button: TButton;
begin
  Button := TButton.Create(Form1);
  Button.Parent := Form1;

  FMyPanel.BringToFront;

  with Button do
  begin
    Caption := 'Button';
    Left := 25;
    Name := 'Button';
    Top  := 15;
    OnMouseDown := ControlMouseDown;

    PaintTo(FMyPanel.Canvas, Left, Top);
    Invalidate;
  end;
end;

If you try running the above, you will see that the TButton we created does not animate or receive focus, but it can respond to MouseDown events we attached in the code above, that is because we are not actually looking at the control, instead we are viewing a graphical copy of the control.

Answer 3

I'm not sure if this is what you're after or not, but Greatis has a Form Designer component. See: http://www.greatis.com/delphicb/formdes/