Delphi中Class of 第二篇

---开发环境Delphi7

----Class of 第一篇 https://www.cnblogs.com/dmqhjp/p/15155742.html

--Unit开始

 1 unit Unit1;
 2 
 3 interface
 4 
 5 uses
 6   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 7   Dialogs, StdCtrls;
 8 
 9 type
10   TForm1 = class(TForm)
11     Button1: TButton;
12     procedure Button1Click(Sender: TObject);
13   private
14     { Private declarations }
15   public
16     { Public declarations }
17   end;
18 
19 var
20   Form1: TForm1;
21 
22 implementation
23 
24 var
25   SerialNumber:Integer=1;
26 {$R *.dfm}
27 
28 procedure TForm1.Button1Click(Sender: TObject);
29 var
30   vButton:TButton;
31 begin
32   //这个是不是很神奇？
33   {
34    CreateForm这个不是创建窗体的吗？为啥可以创建按钮！？
35    //TComponentClass= class of TComponent;(在Classes中就有这样的声明)
36    //结合第一篇中说到的，子类型不管第几代，父类都能创建，通过类引用(类的类)达到目的
37    //TButton也是TComponent的N代子类啊！所以这个也可以建立TButton的实例
38 
39     procedure TApplication.CreateForm(InstanceClass: TComponentClass; var Reference);
40     var
41       Instance: TComponent;
42     begin
43       Instance := TComponent(InstanceClass.NewInstance);
44       TComponent(Reference) := Instance;
45       try
46         Instance.Create(Self);
47       except
48         TComponent(Reference) := nil;
49         raise;
50       end;
51       if (FMainForm = nil) and (Instance is TForm) then
52       begin
53         TForm(Instance).HandleNeeded;
54         FMainForm := TForm(Instance);
55       end;
56     end;
57 
58   }
59   Application.CreateForm(TButton,vButton);
60   vButton.Parent:=Self;
61   vButton.Height:=20;
62   vButton.Width:=80;
63   vButton.Left:=100;
64   vButton.Top:=10+30*(SerialNumber-1);
65   vButton.Name:='Button_'+inttostr(SerialNumber);
66   Inc(SerialNumber);
67 end;
68 
69 end.

------unit结束

----Form开始

 1 object Form1: TForm1
 2   Left = 757
 3   Top = 557
 4   Width = 381
 5   Height = 416
 6   Caption = 'Form1'
 7   Color = clBtnFace
 8   Font.Charset = DEFAULT_CHARSET
 9   Font.Color = clWindowText
10   Font.Height = -11
11   Font.Name = 'MS Sans Serif'
12   Font.Style = []
13   OldCreateOrder = False
14   PixelsPerInch = 96
15   TextHeight = 13
16   object Button1: TButton
17     Left = 8
18     Top = 16
19     Width = 75
20     Height = 25
21     Caption = 'Button1'
22     TabOrder = 0
23     OnClick = Button1Click
24   end
25 end

----Form结束