在运行时按需更改组件类 [英] Changing component class at run-time on demand

问题描述

我的问题类似于这里的想法:替换 delphi 中的组件类.
但我需要根据需要更改特定组件类.
这是一些伪演示代码:

My Question is similar to the idea here: Replacing a component class in delphi.
But I need to change a specific component(s) class on demand.
Here is some pseudo demo code:

unit Unit1;

TForm1 = class(TForm)
  ImageList1: TImageList;
  ImageList2: TImageList;
private
  ImageList3: TImageList;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ImageList3 := TImageList.Create(Self);
  // all instances of TImageList run as usual
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Unit2.MakeSuperImageList(ImageList2);
  Unit2.MakeSuperImageList(ImageList3);
  // from now on ONLY ImageList2 and ImageList3 are TSuperImageList
  // ImageList1 is unchanged
end;

<小时>

unit Unit2;

type
  TSuperImageList = class(Controls.TImageList)
  protected
    procedure DoDraw(Index: Integer; Canvas: TCanvas; X, Y: Integer;
      Style: Cardinal; Enabled: Boolean = True); override;
  end;

procedure TSuperImageList.DoDraw(Index: Integer; Canvas: TCanvas; X, Y: Integer;
  Style: Cardinal; Enabled: Boolean = True);
var
  Icon: TIcon;
begin
  Icon := TIcon.Create;
  try
    Self.GetIcon(Index, Icon);
    Canvas.Draw(X, Y, Icon);
  finally
    Icon.Free;
  end;
end;

procedure MakeSuperImageList(ImageList: TImageList);
begin
  // TImageList -> TSuperImageList
end;

<小时>

注意:明确地说，我想更改一些实例，但不是所有，所以中介层类不会做.

---

Note: Just to be clear, I want to change some instances, but not all, so interposer class will not do.

推荐答案

这比想象中容易(感谢 Hallvard 的博客 - Hack#14:在运行时更改对象的类):

This is easier as thought (thanks to Hallvard's Blog - Hack#14: Changing the class of an object at run-time):

procedure PatchInstanceClass(Instance: TObject; NewClass: TClass);
type
  PClass = ^TClass;
begin
  if Assigned(Instance) and Assigned(NewClass)
    and NewClass.InheritsFrom(Instance.ClassType)
    and (NewClass.InstanceSize = Instance.InstanceSize) then
  begin
    PClass(Instance)^ := NewClass;
  end;
end;

type
  TMyButton = class(TButton)
  public
    procedure Click; override;
  end;

procedure TMyButton.Click;
begin
  ShowMessage('Click!');
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  PatchInstanceClass(Button1, TMyButton);
end;

这篇关于在运行时按需更改组件类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！