delphi – 如何链接“并行”类层次结构？

发布时间：2020-12-15 09:23:43 所属栏目：大数据来源：网络整理

导读：我有一个小类层次结构,其中每个类对应于某个TComponent后代(比如基类TDefaultFrobber与后代TActionFrobber和TMenuItemFrobber,分别对应于TComponent,TCustomAction和TMenuItem).现在我想要一个像这样的工厂(？)函数： function CreateFrobber(AComponent: TC

我有一个小类层次结构,其中每个类对应于某个TComponent后代(比如基类TDefaultFrobber与后代TActionFrobber和TMenuItemFrobber,分别对应于TComponent,TCustomAction和TMenuItem).现在我想要一个像这样的工厂(？)函数：

function CreateFrobber(AComponent: TComponent): IFrobber;
begin
  if AComponent is TCustomAction then
    Result := TActionFrobber.Create(TCustomAction(AComponent))
  else if AComponent is TMenuItem then
    Result := TMenuItemFrobber.Create(TMenuItem(AComponent))
  else
    Result := TDefaultFrobber.Create(AComponent);
end;

我可以以某种方式重构这个以使用虚函数或类似的东西而不是if-else级联或RTTI吗？

编辑：我现在的解决方案：

unit Frobbers;

interface

uses
  Classes;

type
  IComponentFrobber = interface
  end;

  TComponentFrobberClass = class of TComponentFrobber;

  TComponentFrobber = class(TInterfacedObject,IComponentFrobber)
  strict private
    FComponent: TComponent;
  protected
    constructor Create(AComponent: TComponent);
    property Component: TComponent read FComponent;
  public
    class function FindFrobberClass(AComponentClass: TComponentClass): TComponentFrobberClass; overload; static;
    class function FindFrobberClass(AComponent: TComponent): TComponentFrobberClass; overload; static;
    class procedure RegisterFrobber(AComponentClass: TComponentClass; AFrobberClass: TComponentFrobberClass); static;
  end;

implementation

uses
  ActnList,Menus;

type
  TComponentFrobberRegistryItem = record
    ComponentClass: TComponentClass;
    FrobberClass: TComponentFrobberClass;
  end;

var
  FComponentFrobberRegistry: array of TComponentFrobberRegistryItem;

class function TComponentFrobber.FindFrobberClass(AComponentClass: TComponentClass): TComponentFrobberClass;
var
  i: Integer;
begin
  // Search backwards,so that more specialized frobbers are found first:
  for i := High(FComponentFrobberRegistry) downto Low(FComponentFrobberRegistry) do
    if FComponentFrobberRegistry[i].ComponentClass = AComponentClass then
    begin
      Result := FComponentFrobberRegistry[i].FrobberClass;
      Exit;
    end;
  Result := nil;
end;

constructor TComponentFrobber.Create(AComponent: TComponent);
begin
  inherited Create;
  FComponent := AComponent;
end;

class function TComponentFrobber.FindFrobberClass(AComponent: TComponent): TComponentFrobberClass;
var
  i: Integer;
begin
  // Search backwards,so that more specialized frobbers are found first:
  for i := High(FComponentFrobberRegistry) downto Low(FComponentFrobberRegistry) do
    if AComponent is FComponentFrobberRegistry[i].ComponentClass then
    begin
      Result := FComponentFrobberRegistry[i].FrobberClass;
      Exit;
    end;
  Result := nil;
end;

class procedure TComponentFrobber.RegisterFrobber(AComponentClass: TComponentClass;
  AFrobberClass: TComponentFrobberClass);
var
  i: Integer;
begin
  Assert(FindFrobberClass(AComponentClass) = nil,'Duplicate Frobber class');
  i := Length(FComponentFrobberRegistry);
  SetLength(FComponentFrobberRegistry,Succ(i));
  FComponentFrobberRegistry[i].ComponentClass := AComponentClass;
  FComponentFrobberRegistry[i].FrobberClass := AFrobberClass;
end;

function CreateComponentFrobber(AComponent: TComponent): IComponentFrobber;
var
  FrobberClass: TComponentFrobberClass;
begin
  FrobberClass := TComponentFrobber.FindFrobberClass(AComponent);
  Assert(FrobberClass <> nil);
  Result := FrobberClass.Create(AComponent);
end;

type
  TActionFrobber = class(TComponentFrobber);
  TMenuItemFrobber = class(TComponentFrobber);

initialization
  TComponentFrobber.RegisterFrobber(TCustomAction,TActionFrobber);
  TComponentFrobber.RegisterFrobber(TMenuItem,TMenuItemFrobber);
end.

感谢Cesar,Gamecat和mghie.

解决方法

2意见建议：
创建类对数组,然后就可以得到索引并使用类构造函数对,

var
  ArrayItem: array[0..1] of TComponentClass = (TActionFrobber,TMenuItemFrobber);
  ArrayOwner: array[0..1] of TComponentClass = (TCustomAction,TMenuItem);

function CreateFrobber(AComponent: TComponentClass): IFrobber;
var
  Index: Integer;
begin
  Result:= nil;
  for I := Low(ArrayOwner) to High(ArrayOwner) do
    if AComponent is ArrayOwner[I] then
    begin
      Result:= ArrayItem[I].Create(AComponent);
      Break;
    end;

  if Result = nil then
    Result:= TDefaultFrobber.Create(AComponent);
end;

或使用RTTI ClassName约定,如下所示：

function CreateFrobber(AComponent: TComponentClass): IFrobber;
const 
  FrobberClassSuffix = 'Frobber';
var
  LClass: TComponentClass;
  LComponent: TComponent;
begin
  LClass:= Classes.FindClass(AComponent.ClassName + FrobberClassSuffix);
  if LClass <> nil then 
    LComponent:= LClass.Create(AComponent) 
  else
    LComponent:= TDefaultFrobber.Create(AComponent);

  if not Supports(LComponent,IFrobber,Result) then
    Result:= nil;
end;

（编辑：李大同）

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