调用class种不同形式的函数

Question

我有一个应用程序，其中包括 "main" 表格以及其他四种表格（formA、formB、formC、formD）。四种形式中的每一种都有唯一的 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 事件中，根据我在编辑框中传递的表单名称，我想运行适当的 class 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，但是没有成功。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：

你的 TDictionary 被声明为保存 TForm 对象指针，但你的代码试图插入 TForm 派生的 class 类型。那将无法编译。
您的表单 class 不是从具有 Execute() 方法供它们覆盖的公共基础 class 派生的。因此，您不能只从 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()。

有一些可能的方法可以解决这个问题：

从公共基础 class 中导出您的表单 classes，并将该基础 class 的派生词存储在您的 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;

做类似的事情，但使用 interface 而不是基础 class（这只适用于对象，而不适用于 class 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;

根本不要将 classes/objects 存储在您的 TDictionary 中，而是存储实际的 class 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;

调用class种不同形式的函数

Calling class functions of different forms

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