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）。四种表格中的每一种都有一个独特的class function execute()。

现在，在formD中，我放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，我想运行相应的类函数。

我尝试通过创建TDictionary来实现此任务，其中我添加了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

您的方法存在两个问题：

您的TDictionary被声明为保存TForm个对象指针，但您的代码正在尝试插入TForm - 派生类类型。那将无法编译。
您的表单类不是从具有Execute()方法的公共基类派生的。因此，您无法直接从TDictionary检索值并直接致电Execute。您将不得不求助于使用RTTI来查找和调用Execute()。

有一些可行的方法可以解决这个问题：

从公共基类派生您的Form类，并在TDictionary中存储该基类的派生类：

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而不是基类（这只适用于对象，而不是类类型）：

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;

根本不在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;

调用不同形式的类函数

1 个答案: