Such as: I use delphi10.2.3 wrote a DLL, the DLL, brought a form, and deduced two culvert number for external calls,
One of them is initialized,
One is the call function,
Now found in any other language development program, if it is a simple demo, such as: the window of the application is a simple, call the number two culvert on the form, 90% is no problem, but the call number is much, occasionally appear the situation of the program crashes,
But if it is in a fully functional application calls the DLL is 100%, the second call, the DLL can cause collapse of the main program,
May I express a little mess, I directly with the code below, exclude pleaded:
DLL, I use the form, also use the multithreading, because on the DLL requires interface display effect,

DLL code is as follows:

 
The library leshua. 

USES the 
System. The SysUtils, 
System. Classes, 
Unit1 in 'Unit1. Pas, 
Unit2 in 'Unit2. Pas' {Form2}; 

{$R *. Res} 
Exports 
InitLeshua, 
LeshuaPay; 

The begin 
End. 

Unit 1 code is as follows:

 
The unit Unit1; 

Interface 

USES the 
Winapi. Windows System. SysUtils, System. Classes, System. The Hash, Vcl. 
 Controls,The Vcl. Forms, Vcl. ExtCtrls IdHTTP, IdSSLOpenSSL, IdGlobal, XMLDoc, XMLIntf, 
StrUtils, messages, unit2, IniFiles; 

Type 
Str_thread_date=record 
Ls_djno: string; 
Ls_amount: string; 
Ls_paycode: string; 
end; 

Type 
TMyThread=class (TThread) 
Private 
{Private declarations} 
Protected 
Procedure the Execute; Override. {performed} 
Procedure Run; {statement more than a process, write functional code here again to call the Execute} 
end; 

The function initLeshua (as_shh: PAnsiChar; As_t0: PAnsiChar; Handle: THandle) : Integer; Stdcall; 

The function LeshuaPay (as_djno: PAnsiChar; As_amount: PAnsiChar; As_paycode: PAnsiChar; As_error: PAnsiChar) : Integer; Stdcall; 

The function GetDllPath: string; 

Procedure writeLog (logstr: string); 

Var 
Form2: TForm2; 
Gs_error: string;//error content 
Gi_return: Integer;//return the result & lt; 0 for failure, & gt; Success as a=0 
Lstr_thread_data: str_thread_date; 
AppHandle: THandle; 
OldHandle: THandle; 
Gs_url: string;//request address 
Gs_key: string;//KEY 
Gs_shh: string; No.//merchants 

Implementation 

Var 
MyThread: TMyThread; {statement a thread class object} 

Procedure TMyThread. Execute; 
The begin 
{Place thread code here} 
WriteLog (' start executing thread); 
FreeOnTerminate:=True; {and ran out of the thread automatically annotation} 
WriteLog (' ready to run thread number of culvert run '); 
Run; 
end; 

Procedure TMyThread. Run; 
Var 
I: integer; 
Ls_showtext: string; 
Ls_shh: string; 
Myinifile: TIniFile;//configuration file 
The begin 
WriteLog (' thread number of culvert run start); 

Myinifile:=Tinifile. Create (ExtractFilePath (GetDllPath ()) + 'leshuapay. Ini'); 
Ls_shh:=myinifile Readstring (' system ', 'business_no', '); 
Myinifile. Destroy; 
WriteLog (='+' thread number of culvert run for SHH ls_shh); 

For I:=1 to 10 do 
The begin 
WriteLog (' thread culvert for the run: the first '+ IntToStr (I) +' cycles'); 
The Lock; Form2. Canvas. 
Form2. Panel1. Caption:='first' + IntToStr (I) + 'loops; 
Form2. Canvas. Unlock; 
WriteLog (' thread number of culvert run: delay 1 seconds'); 
Sleep (1000); 
end; 
WriteLog (' thread number of culvert run: ready to close the Form2); 
Form2. Close; 
WriteLog (' end of thread number of culvert run: '); 
end; 

The function initLeshua (as_shh: PAnsiChar; As_t0: PAnsiChar; Handle: THandle) : Integer; Stdcall; 
Var 
Ls_shh: PAnsiChar; 
Myinifile: TIniFile;//configuration file 
The begin 
If (appHandle=0) then 
AppHandle:=handle; 

Myinifile:=Tinifile. Create (ExtractFilePath (GetDllPath ()) + 'leshuapay. Ini'); 
Myinifile. Writestring (' system ', 'business_no as_shh); 
Myinifile. Destroy; 

Gs_key:='ADB8145F4D8A820D30B20B1930'; 
Gs_url:='https://paygate.shuazf.com/cgi-bin/pay_gateway.cgi'; 
WriteLog (' initialization: merchant number=[' + as_shh +], request address=[' + gs_url + '] '); 
Result:=1; 
end; 

The function LeshuaPay (as_djno: PAnsiChar; As_amount: PAnsiChar; As_paycode: PAnsiChar; As_error: PAnsiChar) : Integer; Stdcall; 
Var 
Ls_error: string; 
The begin 
WriteLog (' begin paying culvert number); 
MyThread:=TMyThread. Create (False); {instantiation thread class, run immediately when False and True can add MyThread. When Resume to start the} 
WriteLog (' open the thread end '); 
OldHandle:=Application. Handle; 
Application. Handle:=appHandle; 
WriteLog (' form instance China); 
Application CreateForm (TForm2, Form2); 
Try 
WriteLog (' display form); 
Form2. ShowModal; 
The finally 
WriteLog (' ready to release resources'); 
Form2. Free; 
WriteLog (' form released all '); 
Application. Handle:=oldHandle; 
WriteLog (' handle reduction); 
end; 

Ls_error:='WXZF | 0000290005619263'; 
WriteLog (' copy to return information); 
StrPCopy (as_error, AnsiString (ls_error)); 
WriteLog (' pay culvert for return); 
Result:=1; 
end; 

The function GetDllPath: string; 
Var 
ModuleName: string; 
The begin 
SetLength (ModuleName, 255); 
//Dll's own path 
GetModuleFileName (HInstance, PChar (ModuleName), Length (ModuleName)); 
Result:=PChar (ModuleName); 
end; 

Procedure writeLog (logstr: string); 
Var 
Filev: TextFile; 
Path, name, logfile: string; 
The begin 
//write log 
Path:=ExtractFilePath (GetDllPath ()) + 'log \'; 
If not FileExists ((path)) then 
ForceDirectories (path); 

Name:='LESHUA_ + FormatDateTime (' yyyymmdd', now);//date 
The logfile: path + name +='. TXT ';//log access path 
Name:=logfile; 

If FileExists (logfile) then 
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