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How to open additional files in an already running application

I am writing an MDI text editor and I was wondering how I can open all text files using my application. (If I link te * .txt to my application, I want to have every time someone double-click the txt file to open it in my application, in a new child window)

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4 answers


I The following implementation is currently implemented for this:

Dpr file

var
  PrevWindow : HWND;
  S : string;
  CData : TCopyDataStruct;

begin
  PrevWindow := 0;
  if OpenMutex(MUTEX_ALL_ACCESS, False, 'YourUniqueStringHere') <> 0 then
    begin
      PrevWindow:=FindWindow('TYourMainFormClassName', nil);

      if IsWindow(PrevWindow) then
      begin
        SendMessage(PrevWindow, WM_SYSCOMMAND, SC_RESTORE, 0);
        BringWindowToTop(PrevWindow);
        SetForegroundWindow(PrevWindow);

        if FileExists(ParamStr(1)) then
        begin
          S:=ParamStr(1);
          CData.dwData:=0;
          CData.lpData:=PChar(S);
          CData.cbData:=1+Length(S);

          SendMessage(PrevWindow, WM_COPYDATA, 0, DWORD(@CData) );
        end;
      end;
    end
  else
    CreateMutex(nil, False, 'YourUniqueStringHere');

in the main module, we handle the WM_COPYDATA message:



we declare a message handler

procedure ReceiveData_Handler ( var msg : TWMCopyData ) ; message WM_COPYDATA;


procedure TForm1.ReceiveData_Handler(var msg: TWMCopyData);
begin
  // Your file name is in the msg.CopyDataStruct.lpData
  // Cast it to PChar();
end;

Hope it works for you.

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The solution to this is also a solution to prevent more than one application from running at the same time. What you want to do is first detect that the program is already running, then pass the parameter to the running application and close.



There are several methods to determine if your application is running. After you choose the one that matches your programming settings, the next step is to submit a file to open your running program. This can be done through named pipes, messages (although messages do not work in Vista / Win7 if the application is running in a different security context), or any other IPC method .

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Review the Windows DDE documentation . I am changing the DDEExec options in the registry so the wrapper correctly directs the open file to my existing application instance. The following code makes the necessary changes to the registry. Replace "AppName" with your application name (and remove the brackets).

     // add the ddeexec key
     if not reg.OpenKey( '\Software\Classes\<AppName>.file\shell\open\ddeexec', true ) then
        raise Exception.Create( 'Error setting ddeexec key' );

     try
        reg.WriteString( '', 'FileOpen("""%1""")' );
     finally
        reg.CloseKey;
     end;

     // modify the command key to not include the parameter, as we don't use it
     if not reg.OpenKey( '\Software\Classes\<AppName>.file\shell\Open\command', true ) then
        raise Exception.Create( 'Error opening command key.' );

     try
        strTemp := reg.ReadString( '' );

        strTemp := StringReplace( strTemp, '"%1"', '', [] );
        reg.WriteString( '', strTemp );

     finally
        reg.CloseKey;
     end;
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I don't know the Delphi version you are using, but in Delphi 7, in the examples folder, you will see an example MDI editor.

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