The MDI child form that encapsulates VCL in the DLL dynamic link library in Delphi

Not much said, look at the code should understand, once I encountered problems, now let everyone share!

Here is the part of the engineering document:

Encapsulating an MDI child form in a DLL requires you to override the DLL entry function, as shown in the following code:

1var
2　 DllApp: TApplication;//定义保存原DLL的TApplication对象
3　 DllScr: TScreen;//定义保存原DLL的TScreen对象
4
5procedure UnProcDll(Reason: Integer); register;
6//重新定义DLL入口函数
7begin
8　 if Reason = DLL_PROCESS_DETACH then
9　 begin
10　　　 Application := DllApp;
11　　　 Screen := DllScr;
12　 end;
13end;
14
15//初始化区
16begin
17　 DllApp := Application;//备份原DLL的TApplication对象
18　 DllScr := Screen;//备份原DLL的TScreen对象
19　 DllProc := @UnProcDll;//将重写后的入口函数地址付给DLLProc
20end.

Here is the function to be exported, written in the engineering file or in the interface section of a unit:

1function ShowForm(App: TApplication; Scr: TScreen; Owner: TForm):TForm; export; stdcall;
2begin
3　 //下面的这两个变量是必须的
4　 Application := App;//这个就是调用的时候对Application对象重新赋值
5　 Screen := Scr;//对Screen对象赋值
6　 //函数自定义代码
7　 if not Assigned(Form1) then
8　 begin
9　　　 //Application.CreateForm(TForm1, Form1);
10　　　 Form1 := TForm1.Create(Owner);
11　　　 Result := Form1;
12　 end
13　 else
14　　　 Result := Form1;
15　 //函数自定义代码结束
16end;

Finally, in the engineering file to export this function is OK.

1//最后导出这个函数
2exports
3　　 ShowForm;