{
I set up a file type (.myfile) to be run by my program, and everything works
okay. The program opens it fine. The problem is, if I double-click some file
on my HD, it opens a new instance of my app, rather than sending the file to
the already opened one. How can I fix this?
}
{
Example for using DDE to open files from Explorer:
http://codecentral.borland.com/codecentral/ccweb.exe/finder
and search for submission ID 17787
}
{That is the comprehensive solution . There are simpler ones but they tend
to get problems if more than one file is opened at once from Explorer. Those
problems can be handled, but it gets a bit complex to do that.
Basically you proceed like this:
In your programs main block (DPR file) you create a named global kernel
object, e.g. a Mutex or memory-mapped file, using a unique name (e.g. a GUID).
The first instance will create this object successfully and hold on to the
objects handle until it closes. All further instances will detect that the
object already exists, so know that they are not supposed to show up to the
user. But they have to pass over any command-line they may have been handed
from Explorer. They do that by sending a WM_COPYDATA message with the command
line contents to the first instances main window. For that they have to find
the windows handle, for which they use FindWindow with the main forms
classname (which should definitely be somewhat more unique than "Form1"!). The
problem is that the first instance may not have gotten around to creating its
main window yet (if more than one file has been opened from Explorer and the
program was not already running). So the second instance may have to wait in a
loop (using Sleep to suspend itself for a little bit) until the first
instances window shows up.
Bits and pieces of this process have been posted many times on the groups in
the past, but i don't remember if a solution covering all bases was among
them. So since it is Sunday and i'm a wee bit bored let's try for a generic
solution. The meat is in the PBOnceOnly unit given further down. I explain its
usage first. Note that this has been tested on Windows 2000 only, and not very
extensively either.
In the projects DPR file you have code looking like this:
}
program OneInstanceDemo;
uses
Forms,
Unit1 in 'Unit1.pas' {OneInstanceDemoMainform},
PBOnceOnly;
{$R *.res}
const
ProcessName = '{53F0DF5B-B69D-40B7-9B2C-A9E515CCFC80}';
begin
if AlreadyRunning(ProcessName, TOneInstanceDemoMainform) then
Exit;
Application.Initialize;
Application.CreateForm(TOneInstanceDemoMainform, OneInstanceDemoMainform);
Application.Run;
end.
{You can create a GUID for the processname via Ctrl-Shift-G in the IDE, just
remove the enclosing square brackets.
The main form needs a message handler for WM_COPYDATA, and also a method to
handle a command-line parameter. The example form only shows the passed
parameter in a memo.}
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
ComCtrls, Buttons, StdCtrls;
type
TOneInstanceDemoMainform = class(TForm)
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
private
procedure WMCopyData(var msg: TWMCopyData); message WM_COPYDATA;
procedure HandleParameter(const param: string);
public
{ Public declarations }
end;
var
OneInstanceDemoMainform: TOneInstanceDemoMainform;
implementation
uses PBOnceOnly;
{$R *.DFM}
procedure TOneInstanceDemoMainform.FormCreate(Sender: TObject);
begin
memo1.Text := Format('Thread ID: %x'#13#10, [GetCurrentThreadID]);
HandleCommandline(HandleParameter);
end;
procedure TOneInstanceDemoMainform.HandleParameter(const param: string);
begin
memo1.Lines.Add(param);
end;
procedure TOneInstanceDemoMainform.WMCopyData(var msg: TWMCopyData);
begin
HandleSendCommandline(msg.CopyDataStruct^, HandleParameter);
end;
end.
{The work of dissecting the passed commandline is left to the PBOnceOnly unit,
since it "knows" how it packaged the parameters in the other instance. The
technique used by the unit is rather simple: the first instance creates a
memory mapped file and stores its main threads thread ID into this file. It
cannot store the main forms handle since the form has not been created yet
when AlreadyRunning is called. It would be a bad idea anyway since a forms
handle can change over the form objects lifetime. The second instance gets
this handle, uses EnumThreadWindows to find the first instances main form
handle (doing this way avoids problems with the IDE designers form instance
during development), packages the command line and sends it over to the found
window. The second instance will then terminate since AlreadyRunning returns
true in it. It never creates any of the autocreated forms or datamodules and
never enters its message loop.}
{== PBOnceOnly ========================================================}
{: Implements a function to detect a running instance of the program and
(optionally) pass over any command line to the first instances main
window.
@author Dr. Peter Below
@desc Version 1.0 created 2003-02-23
Last modified 2003-02-23
If a command line has to be passed over we need the window handle of the
first instances main window, to send a WM_COPYDATA message to it. Since
the first instance may not have gotten around to creating its main
form window handle yet we retry a couple of times and wait a bit in
between. This process can be configured by setting the MAX_RETRIES and
RETRIES_INTERVAL variables before calling AlreadyRunning. }
{======================================================================}
{$BOOLEVAL OFF} {Unit depends on shortcut boolean evaluation}
unit PBOnceOnly;
interface
uses Windows;
var
{: Specifies how often we retry to find the first instances main
window. }
MAX_RETRIES: Integer = 10;
{: Specifies how long, in milliseconds, we sleep between retries. }
RETRIES_INTERVAL: Integer = 1000;
{-- AlreadyRunning ----------------------------------------------------}
{: Checks for another instance of the program and optionally passes over
this instances command line.
@Param aProcessName is a unique name to be used to identify this program.
@Param aMainformClass is the programs main form class, can be nil.
@Param passCommandline indicates whether to pass the command line, true
by default.
@Param allowMultiuserInstances indicates whether to allow other
instances of the program to run in another user context. Only applies
to Windows terminal server or XP. True by default.
@Returns true if there is another instance running, false if not.
@Precondition The function has not been called already. It must only
be called once per program run.
@Desc Creates a memory mapped file with the passed process name,
optionally with an added 'Global' prefix. If the MMF already existed
we know that this is a second instance. The first instance stores its
main thread ID into the MMF, the second one uses that with
EnumThreadWindows to find the first instances main window and sends
the command line via WM_COPYDATA to this window, if requested.
@Raises Exception if creation of the MMF fails for some reason.
}{ Created 2003-02-23 by P. Below
-----------------------------------------------------------------------}
function AlreadyRunning(const aProcessName: string;
aMainformClass: TClass = nil;
passCommandline: Boolean = true;
allowMultiuserInstances: Boolean = true): Boolean;
type
{: Callback type used by HandleSendCommandline. The callback will
be handed one parameter at a time. }
TParameterEvent = procedure(const aParam: string) of object;
{-- HandleSendCommandline ---------------------------------------------}
{: Dissect a command line passed via WM_COPYDATA from another instance
@Param data contains the data received via WM_COPYDATA.
@Param onParameter is a callback that will be called with every passed
parameter in turn.
@Precondition onParameter <> nil
}{ Created 2003-02-23 by P. Below
-----------------------------------------------------------------------}
procedure HandleSendCommandline(const data: TCopyDataStruct;
onParameter: TParameterEvent);
{-- HandleCommandline -------------------------------------------------}
{: This is a convenience procedure that allows handling of this
instances command line parameters to be done the same way as
a command line send over from another instance.
@Param onParameter will be called for every command line parameter in turn.
@Precondition onParameter <> nil
}{ Created 2003-02-23 by P. Below
-----------------------------------------------------------------------}
procedure HandleCommandline(onParameter: TParameterEvent);
implementation
uses Messages, Classes, Sysutils;
{ The THandledObject and TShareMem classes come from the D6 IPCDemos
demo project. }
type
THandledObject = class(TObject)
protected
FHandle: THandle;
public
destructor Destroy; override;
property Handle: THandle read FHandle;
end;
{ This class simplifies the process of creating a region of shared memory.
In Win32, this is accomplished by using the CreateFileMapping and
MapViewOfFile functions. }
TSharedMem = class(THandledObject)
private
FName: string;
FSize: Integer;
FCreated: Boolean;
FFileView: Pointer;
public
constructor Create(const Name: string; Size: Integer);
destructor Destroy; override;
property Name: string read FName;
property Size: Integer read FSize;
property Buffer: Pointer read FFileView;
property Created: Boolean read FCreated;
end;
procedure Error(const Msg: string);
begin
raise Exception.Create(Msg);
end;
{ THandledObject }
destructor THandledObject.Destroy;
begin
if FHandle <> 0 then
CloseHandle(FHandle);
end;
{ TSharedMem }
constructor TSharedMem.Create(const Name: string; Size: Integer);
begin
try
FName := Name;
FSize := Size;
{ CreateFileMapping, when called with $FFFFFFFF for the handle value,
creates a region of shared memory }
FHandle := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0,
Size, PChar(Name));
if FHandle = 0 then abort;
FCreated := GetLastError = 0;
{ We still need to map a pointer to the handle of the shared memory region
}
FFileView := MapViewOfFile(FHandle, FILE_MAP_WRITE, 0, 0, Size);
if FFileView = nil then abort;
except
Error(Format('Error creating shared memory %s (%d)', [Name,
GetLastError]));
end;
end;
destructor TSharedMem.Destroy;
begin
if FFileView <> nil then
UnmapViewOfFile(FFileView);
inherited Destroy;
end;
var
{ This object is destroyed by the unit finalization }
ProcessInfo: TSharedMem = nil;
{ Check if we are running in a terminal client session }
function IsRemoteSession: Boolean;
const
sm_RemoteSession = $1000; { from WinUser.h }
begin
Result := GetSystemMetrics(sm_RemoteSession) <> 0;
end;
{ Check if we are running on XP or a newer version. XP is Windows NT 5.1 }
function IsXP: Boolean;
begin
Result :=
(Sysutils.Win32Platform = VER_PLATFORM_WIN32_NT)
and
((Sysutils.Win32MajorVersion > 5)
or
((Sysutils.Win32MajorVersion = 5)
and
(Sysutils.Win32MinorVersion > 0)
)
);
end;
{ Check if we are running in a Windows terminal client session or on
Windows XP. }
function IsWTSOrXP: Boolean;
begin
Result := IsRemoteSession or IsXP
end;
type
{ Helper class to hold classname and found window handle for
EnumThreadWindows }
TEnumhelper = class
public
FClassname: string;
FWnd: HWND;
constructor Create(const aClassname: string);
function Matches(wnd: HWND): Boolean;
end;
constructor TEnumhelper.Create(const aClassname: string);
begin
inherited Create;
FClassname := aClassname;
end;
function TEnumhelper.Matches(wnd: HWND): Boolean;
var
classname: array[0..127] of Char;
begin
classname[0] := #0;
Windows.GetClassname(wnd, classname, sizeof(classname));
Result := AnsiSametext(Fclassname, classname);
if result then
FWnd := wnd;
end;
function EnumProc(wnd: HWND; helper: TEnumHelper): BOOL; stdcall;
begin
Result := not helper.Matches(wnd);
end;
function FindFirstInstanceMainform(const aClassname: string): HWND;
var
threadID: DWORD;
helper: TEnumHelper;
begin
threadID := PDWORD(Processinfo.FFileView)^;
helper := TEnumHelper.Create(aclassname);
try
EnumThreadWindows(threadID, @EnumProc, Integer(helper));
Result := helper.FWnd;
finally
helper.Free;
end;
end;
function AlreadyRunning(const aProcessName: string;
aMainformClass: TClass = nil;
passCommandline: Boolean = true;
allowMultiuserInstances: Boolean = true): Boolean;
function Processname: string;
begin
if not allowMultiuserInstances and IsWTSorXP then
Result := 'Global\' + aProcessName
else
Result := aProcessName;
end;
procedure StoreThreadID;
begin
PDWORD(ProcessInfo.FFileView)^ := GetCurrentThreadID;
end;
function GetCommandline: string;
var
sl: TStringlist;
i: Integer;
begin
if ParamCount = 1 then
Result := ParamStr(1)
else begin
sl := TStringlist.Create;
try
for i := 1 to ParamCount do
sl.Add(ParamStr(i));
Result := sl.Text;
finally
sl.free;
end; { Finally }
end;
end;
procedure DoPassCommandline;
var
wnd: HWND;
S: string;
copydata: TCopyDataStruct;
retries: Integer;
begin
retries := 0;
repeat
wnd := FindFirstInstanceMainform(aMainformclass.Classname);
if wnd <> 0 then
begin
S := GetCommandline;
copydata.dwData := Paramcount;
copydata.cbData := Length(S) + 1;
copydata.lpData := PChar(S);
SendMessage(wnd, WM_COPYDATA, 0, integer(@copydata));
end
else begin
Inc(retries);
Sleep(RETRIES_INTERVAL);
end;
until (wnd <> 0) or (retries > MAX_RETRIES);
end;
begin
Assert(not Assigned(ProcessInfo),
'Do not call AlreadyRunning more than once!');
ProcessInfo := TSharedMem.Create(Processname, Sizeof(DWORD));
Result := not ProcessInfo.Created;
if Result then
begin
if passCommandline and Assigned(aMainformClass) and (ParamCount > 0) then
DoPassCommandline;
end
else
StoreThreadID;
end;
procedure HandleSendCommandline(const data: TCopyDataStruct;
onParameter: TParameterEvent);
var
i: Integer;
sl: TStringlist;
begin
Assert(Assigned(onParameter), 'OnParameter cannot be nil');
if data.dwData = 1 then
onParameter(PChar(data.lpData))
else
begin
sl := TStringlist.Create;
try
sl.Text := PChar(data.lpData);
for i := 0 to sl.Count - 1 do
onParameter(sl[i]);
finally
sl.Free;
end; { Finally }
end;
end;
procedure HandleCommandline(onParameter: TParameterEvent);
var
i: Integer;
begin
Assert(Assigned(onParameter), 'OnParameter cannot be nil');
for i := 1 to ParamCount do
onParameter(ParamStr(i));
end;
initialization
finalization
ProcessInfo.Free;
end.