How to enforce VCL style overrides when dynamically creating components? - delphi

Question

In Delphi XE2 I have successfully created overrides for the VCL Styles for a custom component class I have created. What I have found though is that the styles do not appear to apply during runtime creation of the controls.
To be specific I have extended TPanel and am filling a TScrollBox with dynamically created Panels, setting each to a specific color. I also use the API to suspend redraws on the ScrollBox during the creation process.
When the loading is complete, I am left with TPanels set to clWindow (visually) but when I drag and drop the TPanel to another location/control the colors I set in code "kick in". So something is not letting/allowing those colors to apply... or the Panels simply are not refreshing.
So I'm not quite sure if there is a "refresh" I need to call with VCL Style overrides on dynamic component creation, or if the suspension of redraws on TScrollBox are causing interference with the color not updating on the Panel when created.. since it is a child of the suspended ScrollBox.
I'm wondering if there is just a simple & known "gotcha" I am overlooking with what I am trying to do.
I've stripped down the project to bare essentials and it still has the issue.
This is a simple extension of TPanel adding a label.
unit InfluencePanel;
interface
uses
System.SysUtils, System.Classes, Vcl.Forms, Vcl.Controls, Vcl.StdCtrls, Vcl.ExtCtrls,
Vcl.Graphics;
type
TInfluencePanel = class(TPanel)
private
{ Private declarations }
oCaptionLabel : TLabel;
FLabelCaption : String;
procedure SetLabelCaption(sCaption : String);
protected
{ Protected declarations }
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
property LabelCaption : string read FLabelCaption write SetLabelCaption;
published
{ Published declarations }
end;
procedure Register;
implementation
constructor TInfluencePanel.Create(AOwner: TComponent);
begin
inherited;
oCaptionLabel := TLabel.Create(Self);
with oCaptionLabel do
begin
Caption := 'Caption';
Top := 0;
Left := 0;
Align := alTop;
WordWrap := True;
Parent := Self;
end;
end;
procedure TInfluencePanel.SetLabelCaption(sCaption: string);
begin
FLabelCaption := sCaption;
if oCaptionLabel <> nil then oCaptionLabel.Caption := FLabelCaption;
end;
procedure Register;
begin
RegisterComponents('Influence Elements', [TInfluencePanel]);
end;
end.
This is the simple project that should show the issue. Button 1 loads five instances of the TInfluencePanel into ScrollBox1. They appear with the default windows color and no style instead of the color in code. Button2 moves the controls to ScrollBox2 where they appear with the coded colors. This has all the suspended redraws taken out, etc.
unit Unit1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants,
System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs,
Vcl.StdCtrls, Vcl.ExtCtrls, Vcl.Themes, InfluencePanel;
type
TInfluencePanelStyleHookColor = class(TEditStyleHook)
private
procedure UpdateColors;
protected
procedure WndProc(var Message: TMessage); override;
public
constructor Create(AControl: TWinControl); override;
end;
type
TForm1 = class(TForm)
ScrollBox1: TScrollBox;
ScrollBox2: TScrollBox;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
uses
Vcl.Styles;
type
TWinControlH= class(TWinControl);
constructor TInfluencePanelStyleHookColor.Create(AControl: TWinControl);
begin
inherited;
UpdateColors;
end;
procedure TInfluencePanelStyleHookColor.UpdateColors;
var
LStyle: TCustomStyleServices;
begin
if Control.Enabled then
begin
Brush.Color := TWinControlH(Control).Color;
FontColor := TWinControlH(Control).Font.Color;
end
else
begin
LStyle := StyleServices;
Brush.Color := LStyle.GetStyleColor(scEditDisabled);
FontColor := LStyle.GetStyleFontColor(sfEditBoxTextDisabled);
end;
end;
procedure TInfluencePanelStyleHookColor.WndProc(var Message: TMessage);
begin
case Message.Msg of
CN_CTLCOLORMSGBOX..CN_CTLCOLORSTATIC:
begin
UpdateColors;
SetTextColor(Message.WParam, ColorToRGB(FontColor));
SetBkColor(Message.WParam, ColorToRGB(Brush.Color));
Message.Result := LRESULT(Brush.Handle);
Handled := True;
end;
CM_ENABLEDCHANGED:
begin
UpdateColors;
Handled := False;
end
else
inherited WndProc(Message);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
iPanel, iLastPosition : Integer;
oPanel : TInfluencePanel;
begin
iLastPosition := 0;
for iPanel := 1 to 5 do
begin
oPanel := TInfluencePanel.Create(ScrollBox1);
with oPanel do
begin
Align := alLeft;
Left := iLastPosition;
Width := 90;
Parent := ScrollBox1;
Color := RGB(200,100,iPanel*10);
LabelCaption := 'My Panel ' + IntToStr(iPanel);
Margins.Right := 5;
AlignWithMargins := True;
end;
iLastPosition := iLastPosition + 90;
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
var
iPanel : Integer;
begin
for iPanel := ScrollBox1.ControlCount - 1 downto 0 do
begin
if ScrollBox1.Controls[iPanel].ClassType = TInfluencePanel then
TInfluencePanel(ScrollBox1.Controls[iPanel]).Parent := ScrollBox2;
end;
end;
initialization
TStyleManager.Engine.RegisterStyleHook(TInfluencePanel,TInfluencePanelStyleHookColor);
end.

Answer 1

Your Style hook has not effect in the paint process because The TPanel doesn't use a style hook to draw the control. you must override the paint method in your component like so.
unit InfluencePanel;
interface
uses
System.SysUtils, System.Classes, Vcl.Forms, Vcl.Controls, Vcl.StdCtrls, Vcl.ExtCtrls,
Vcl.Graphics;
type
TInfluencePanel = class(TPanel)
private
{ Private declarations }
oCaptionLabel : TLabel;
FLabelCaption : String;
procedure SetLabelCaption(sCaption : String);
protected
procedure Paint; override;
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
property LabelCaption : string read FLabelCaption write SetLabelCaption;
published
{ Published declarations }
end;
procedure Register;
implementation
uses
Winapi.Windows,
System.Types,
Vcl.Themes;
constructor TInfluencePanel.Create(AOwner: TComponent);
begin
inherited;
oCaptionLabel := TLabel.Create(Self);
with oCaptionLabel do
begin
Caption := 'Caption';
Top := 0;
Left := 0;
Align := alTop;
WordWrap := True;
Parent := Self;
end;
end;
procedure TInfluencePanel.SetLabelCaption(sCaption: string);
begin
FLabelCaption := sCaption;
if oCaptionLabel <> nil then oCaptionLabel.Caption := FLabelCaption;
end;
procedure TInfluencePanel.Paint;
const
Alignments: array[TAlignment] of Longint = (DT_LEFT, DT_RIGHT, DT_CENTER);
VerticalAlignments: array[TVerticalAlignment] of Longint = (DT_TOP, DT_BOTTOM, DT_VCENTER);
var
Rect: TRect;
LColor: TColor;
LStyle: TCustomStyleServices;
LDetails: TThemedElementDetails;
TopColor : TColor;
BottomColor : TColor;
LBaseColor : TColor;
LBaseTopColor : TColor;
LBaseBottomColor: TColor;
Flags: Longint;
procedure AdjustColors(Bevel: TPanelBevel);
begin
TopColor := LBaseTopColor;
if Bevel = bvLowered then
TopColor := LBaseBottomColor;
BottomColor := LBaseBottomColor;
if Bevel = bvLowered then
BottomColor := LBaseTopColor;
end;
begin
Rect := GetClientRect;
LBaseColor := Color;//use the color property value to get the background color.
LBaseTopColor := clBtnHighlight;
LBaseBottomColor := clBtnShadow;
LStyle := StyleServices;
if LStyle.Enabled then
begin
LDetails := LStyle.GetElementDetails(tpPanelBevel);
if LStyle.GetElementColor(LDetails, ecEdgeHighLightColor, LColor) and (LColor <> clNone) then
LBaseTopColor := LColor;
if LStyle.GetElementColor(LDetails, ecEdgeShadowColor, LColor) and (LColor <> clNone) then
LBaseBottomColor := LColor;
end;
if BevelOuter <> bvNone then
begin
AdjustColors(BevelOuter);
Frame3D(Canvas, Rect, TopColor, BottomColor, BevelWidth);
end;
if not (LStyle.Enabled and (csParentBackground in ControlStyle)) then
Frame3D(Canvas, Rect, LBaseColor, LBaseColor, BorderWidth)
else
InflateRect(Rect, -Integer(BorderWidth), -Integer(BorderWidth));
if BevelInner <> bvNone then
begin
AdjustColors(BevelInner);
Frame3D(Canvas, Rect, TopColor, BottomColor, BevelWidth);
end;
with Canvas do
begin
if not LStyle.Enabled or not ParentBackground then
begin
Brush.Color := LBaseColor;
FillRect(Rect);
end;
if ShowCaption and (Caption <> '') then
begin
Brush.Style := bsClear;
Font := Self.Font;
Flags := DT_EXPANDTABS or DT_SINGLELINE or
VerticalAlignments[VerticalAlignment] or Alignments[Alignment];
Flags := DrawTextBiDiModeFlags(Flags);
if LStyle.Enabled then
begin
LDetails := LStyle.GetElementDetails(tpPanelBackground);
if not LStyle.GetElementColor(LDetails, ecTextColor, LColor) or (LColor = clNone) then
LColor := Font.Color;
LStyle.DrawText(Handle, LDetails, Caption, Rect, TTextFormatFlags(Flags), LColor)
end
else
DrawText(Handle, Caption, -1, Rect, Flags);
end;
end;
end;
procedure Register;
begin
RegisterComponents('Influence Elements', [TInfluencePanel]);
end;
end.
Also in the runtime creation set the ParentBackground property to False
for iPanel := 1 to 5 do
begin
oPanel := TInfluencePanel.Create(ScrollBox1);
with oPanel do
begin
Align := alLeft;
Left := iLastPosition;
Width := 90;
Parent := ScrollBox1;
ParentBackground:=False;// <----
Color := RGB(200,100,iPanel*20);
LabelCaption := 'My Panel ' + IntToStr(iPanel);
Margins.Right := 5;
AlignWithMargins := True;
end;
iLastPosition := iLastPosition + 90;
end;