调用不同形式的类函数

Question

我有一个应用程序，其中包括“主”表单以及其他四种表单（formA、formB、formC、formD）。四种形式中的每一种都有一个唯一的class function execute()。

现在，在 formD 中，我放置了一个编辑框和一个按钮。在按钮的OnClick事件上，根据我在编辑框中传入的表单名称，我想运行相应的类函数。

我试图通过创建一个TDictionary 来实现这个任务，我在其中添加了 3 对值，但它不起作用。具体来说，我做了以下事情：

unit FormDU;

interface

type
  TFormD = class(TForm)
  Edit1: TEdit;
  fcShapeBtn1: TfcShapeBtn;
  .............
  .............
public
  class function execute:boolean;
  ..........
  ..........
end;

var
  FormD: TFormD;
  MyList:TDictionary<string,TForm>;


implementation 

class function TFormD.execute:boolean;
  begin
    FormD:= TFormD.Create(nil);
    MyList:= TDictionary<string,TForm>.create;
    MyList.Add('FormA',TFormA);
    MyList.Add('FormB',TFormB);
    MyList.Add('FormC',TFormC);
    FormD.showmodal;
  end;

procedure TFormD.fcShapeBtn1Click(Sender: TObject); 
begin
  // Here I check whether the text in Edit1 box has the value of one of the
  // keys that are included in the MyList dictionary and if yes I want to 
  // trigger the class function execute of the appropriate form...

  if MyList.ContainsKey(Edit1.text) then  // suppose that text= formA
      MyList.Items[Edit1.text].execute // which doesn't work.... 

  // I thought that the 'Items' method of the dictionary would return back 
  // to me the appropriate form type - which is connected to the specific 
  // key - and thus I could call each form's class function execute()
end;

我不知道如何解决这个问题。

Answer 1

你的方法有两个问题：

1. 您的TDictionary 被声明为持有TForm 对象指针，但您的代码正试图插入TForm 派生类类型。那不会编译。

2. 您的 Form 类不是从一个公共基类派生的，该基类有一个 Execute() 方法供它们覆盖。所以你不能只从TDictionary 中检索一个值并直接调用Execute。您将不得不求助于使用 RTTI 来查找和调用 Execute()。

有一些可能的方法来解决这个问题：

1. 从一个公共基类派生您的 Form 类，并将该基类的派生类存储在您的 TDictionary 中：

   unit FormBaseU;
   
   interface
   
   uses
     Forms;
   
   type
     TFormBase = class(TForm)
     public
       class function Execute: Boolean; virtual;
     end;
   
     TFormBaseClass = class of TFormBase;
   
   implementation
   
   class function TFormBase.Execute: Boolean;
   begin
     Result := False;
   end;
   
   end.
   

   unit FormDU;
   
   interface
   
   uses
     ..., FormBaseU;
   
   type
     TFormD = class(TFormBase)
       Edit1: TEdit;
       fcShapeBtn1: TfcShapeBtn;
       ...
     public
       class function Execute: Boolean; override;
       ...
     end;
   
   var
     FormD: TFormD;
     MyList: TDictionary<string, TFormBaseClass>;
   
   implementation 
   
   uses
     FormAU, FormBU, FormCU;
   
   class function TFormD.Execute: Boolean;
   begin
     MyList := TDictionary<string, TFormBaseClass>.Create;
   
     // make sure TFormA, TFormB, and TFormC all derive
     // from TFormBase and override Execute() ...
     MyList.Add('FormA', TFormA);
     MyList.Add('FormB', TFormB);
     MyList.Add('FormC', TFormC);
   
     FormD := TFormD.Create(nil);
     FormD.ShowModal;
     FormD.Free;
   end;
   
   procedure TFormD.fcShapeBtn1Click(Sender: TObject); 
   var
     FormClass: TFormBaseClass;
   begin
     if MyList.TryGetValue(Edit1.Text, FormClass) then
       FormClass.Execute;
   end;
   

2. 做类似的事情，但使用interface 而不是基类（但这仅适用于对象，不适用于类类型）：

   unit MyIntfU;
   
   interface
   
   type
     IMyIntf = interface
       ['{41BEF2B6-C27F-440E-A88B-9E5CF8840034}']
       function Execute: Boolean;
     end;
   
   implementation
   
   end.
   

   unit FormDU;
   
   interface
   
   uses
     ..., MyIntfU;
   
   type
     TFormD = class(TForm, MyIntf)
       Edit1: TEdit;
       fcShapeBtn1: TfcShapeBtn;
       ...
     public
       function Execute: Boolean;
       ...
     end;
   
   var
     FormD: TFormD;
     MyList: TDictionary<string, TForm>;
   
   implementation 
   
   uses
     FormAU, FormBU, FormCU;
   
   function TFormD.Execute: Boolean;
   begin
     MyList := TDictionary<string, TForm>.Create;
   
     // make sure TFormA, TFormB, and TFormC are all
     // instantiated beforehand and implement IMyIntf ...
     MyList.Add('FormA', FormA);
     MyList.Add('FormB', FormB);
     MyList.Add('FormC', FormC);
   
     FormD := TFormD.Create(nil);
     FormD.ShowModal;
     FormD.Free;
   end;
   
   procedure TFormD.fcShapeBtn1Click(Sender: TObject); 
   var
     Form: TForm;
     Intf: IMyIntf;
   begin
     if MyList.TryGetValue(Edit1.Text, Form) then
     begin
       if Supports(Form, IMyIntf, Intf) then
         Intf.Execute;
     end;
   end;
   

3. 根本不要在TDictionary 中存储类/对象，而是存储实际的类方法：

   unit FormDU;
   
   interface
   
   uses
     ...;
   
   type
     TFormD = class(TForm)
       Edit1: TEdit;
       fcShapeBtn1: TfcShapeBtn;
       ...
     public
       class function Execute: Boolean;
       ...
     end;
   
     TMyClassMethod = function: Boolean of object;
   
   var
     FormD: TFormD;
     MyList: TDictionary<string, TMyClassMethod>;
   
   implementation 
   
   uses
     FormAU, FormBU, FormCU;
   
   class function TFormD.Execute: Boolean;
   begin
     MyList := TDictionary<string, TMyClassMethod>.Create;
   
     MyList.Add('FormA', TFormA.Execute);
     MyList.Add('FormB', TFormB.Execute);
     MyList.Add('FormC', TFormC.Execute);
   
     FormD := TFormD.Create(nil);
     FormD.ShowModal;
     FormD.Free;
   end;
   
   procedure TFormD.fcShapeBtn1Click(Sender: TObject); 
   var
     Meth: TMyClassMethod;
   begin
     if MyList.TryGetValue(Edit1.Text, Meth) then
       Meth;
   end;