MQL5 - Launching a form embedded in a DLL - delphi

Question

In MetaTrader 4/MQL4 I'm able to display a non-modal form (i.e., simple window with string grid) and pass data to this form from an indicator using the DLL interface. Been doing this for a while now and it works perfectly.
Trying to accomplish the same thing in MetaTrader 5/MQL5 but having some trouble. The form displays but immediately goes into an unresponsive state (application not responding).
I did run a test using the same 64-bit DLL on a different 64-bit platform (eSignal 12) and the form loads just fine.
I am using Delphi XE5 Update 2 to build the DLLs. 32-bit for MT4 and 64-bit for MT5. MT5 build is 1881. I created a very simple MQL5 script and Delphi DLL to test it:
MQL5
#import "TestForm.dll"
int showAForm(int hwnd);
int closeAForm();
#import
void OnStart()
{
//---
int hwnd=ChartGetInteger(0,CHART_WINDOW_HANDLE,0);
showAForm(hwnd);
Sleep(5000);
closeAForm();
//---
}
Delphi
library TestForm;
uses
System.SysUtils,
System.Classes,
Windows,
Vcl.Forms, Vcl.Dialogs;
{$R *.res}
var
myForm: TForm;
function showAForm(handle: HWND): integer; stdCall;
var
myHandle: HWND;
begin
myHandle := FindWindow('MetaQuotes::MetaTrader::5.00', nil);
showMessage(IntToStr(myHandle));
try
myForm := TForm.Create(nil);
// myForm:=TForm.CreateParented(myHandle);
// Windows.SetParent(myForm.Handle, myHandle);
myForm.Show;
result := 1;
except
result := -2;
end;
end;
function closeAForm(): integer; stdCall;
begin
myForm.Close();
FreeAndNil(myForm);
result := 1;
end;
exports
showAForm,
closeAForm;
begin
IsMultiThread := true;
end.
I have tried a few different methods of creating the form (nil, parented) but it makes no difference. If I use ShowModal instead of Show the form displays correctly but of course the MT5 GUI is blocked.
No exceptions are generated, and both functions return correctly...it is just that the form itself will not display. Would be grateful if anyone could shed some light on what may be going on, and any possible workarounds.

Answer 1

This is the problem:
showAForm(hwnd);
Sleep(5000);
closeAForm();
Your Sleep(5000); blocks the GUI thread for full 5 seconds.
So you create the form showAForm(), block the GUI thread for 5 seconds, then close the form closeAForm().
The Delphi form needs a working message pump to be able to work properly,
but the Sleep(5000); blocks the thread and doesn't let the message pump to operate.
In Delphi applications, eg. "mydelphiapp.exe", the Application.ProcessMessage function handles a message, and inside the Application.Run procedure, there is code like:
repeat
try
HandleMessage;
except
HandleException(Self);
end;
until Terminated;
To solve the problem, you need to build in Delphi, a message-pumping alternative to Sleep():
procedure MessagePumpingSleep(ADelay:Longword); stdcall;
var
T1, T2, dT : Longword;
begin
T1 := GetTickCount;
repeat
Application.ProcessMessages;
Sleep(1); // this will stop this procedure from consuming 100% CPU.
T2 := GetTickCount;
dT := T2 - T1;
until dT >= ADelay;
end;
exports MessagePumpingSleep;
Then call MessagePumpingSleep(5000) instead of Sleep(5000);
Obviously, to be able to call MessagePumpingSleep(5000), you need to write the proper import code in MQL5 to import the MessagePumpingSleep() -function from the Delphi DLL.