why warning appears when sending bitmap frame into MemoryStream to client? - delphi

Question

Before I explain my problem, I'm sorry for my bad english.
Okay, here my problem. when my Indy server sends bitmap frame to client, always appeared warning like this :
"EAccessViolation at address 004DD42A..."
And error syntax blue highlighted on this :
Athread.Connection.WriteInteger(MemoryStream.Size);
here my source code :
SERVER
procedure TFormHome.TCPServerConnect(AThread: TIdPeerThread);
var
NewClient: PClient;
begin
GetMem(NewClient, SizeOf(TClient));
NewClient.PeerIP := AThread.Connection.Socket.Binding.PeerIP;
NewClient.HostName := GStack.WSGetHostByAddr(NewClient.PeerIP);
NewClient.Connected := Now;
NewClient.LastAction := NewClient.Connected;
NewClient.Thread := AThread;
AThread.Data := TObject(NewClient);
try
Clients.LockList.Add(NewClient);
finally
Clients.UnlockList;
end;
procedure TFormHome.TCPServerExecute(AThread: TIdPeerThread);
var
pesan:string;
begin
pesan:=Athread.Connection.ReadLn;
if pesan = 'video' then
begin
Athread.Connection.WriteLn('send');
Timer1.Enabled:=true;
FormStream.Show;
Athread.Connection.WriteInteger(MemoryStream.Size);
Athread.Connection.OpenWriteBuffer;
Athread.Connection.WriteStream(MemoryStream);
AThread.Connection.CloseWriteBuffer;
FreeAndNil(MemoryStream);
FormStream.Image1.Picture.Bitmap.Free;
end;
procedure TFormHome.Timer1Timer(Sender: TObject);
begin
pic := TBitmap.Create;
MemoryStream:=TMemoryStream.Create;
VideoGrabber.GetBitmap(FormStream.image1.Picture.Bitmap);
pic := FormStream.Image1.Picture.Bitmap;
pic.SaveToStream(MemoryStream);
//Pic.Free;
//FreeAndNil(Pic);
end;
CLIENT
procedure TFormClient.TCPClientConnected(Sender: TObject);
var
pesan : string;
begin
IncomingMessages.Lines.Insert(0,'Connected to Server');
TCPClient.WriteLn('video');
pesan := TCPClient.ReadLn;
if pesan = 'send' then Timer1.Enabled:=true;
end;
procedure TFormClient.Timer1Timer(Sender: TObject);
var
Size : integer;
ReadStream : TMemoryStream;
begin
ReadStream := TMemoryStream.Create;
Size := TCPClient.ReadInteger;
TCPClient.ReadStream(ReadStream,Size,True);
Image1.Picture.Bitmap.LoadFromStream(ReadStream);
Image1.Picture.Bitmap.Free;
FreeAndNil(ReadStream);
end;
what's wrong witha my code? i need your help.
Thank you before.. ^^

Answer 1

You are trying to send the TMemoryStream before it has even been created. You can't use TTimer or TForm in a worker thread (which OnExecute is called in). Even if you could, when TTimer is enabled, its OnTimer event is not triggered immediately, but your code is expecting it to be.
You need to re-write your code to delegate all UI work to the main thread, where it belongs. Try something more like this:
Server:
Uses
..., IdSync;
type
TVideoStartNotify = class(TIdNotify)
protected
procedure DoNotify; override;
public
Thread: TIdPeerThread;
end;
procedure TFormHome.TCPServerDisconnect(AThread: TIdPeerThread);
begin
TIdNotify.NotifyMethod(VideoStop);
end;
procedure TFormHome.TCPServerExecute(AThread: TIdPeerThread);
var
pesan: string;
begin
pesan := AThread.Connection.ReadLn;
if pesan = 'videostart' then
begin
AThread.Connection.WriteLn('send');
with TVideoStartNotify.Create do
begin
Thread := AThread;
Notify;
end;
end
else if pesan = 'videostop' then
begin
AThread.Connection.WriteLn('stop');
TIdNotify.NotifyMethod(VideoStop);
end;
end;
procedure TVideoStartNotify.DoNotify;
begin
FormHome.VideoStart(Thread);
end;
procedure TFormHome.VideoStart(AThread: TIdPeerThread);
begin
ThreadToSendTo := AThread;
Timer1.Enabled := true;
FormStream.Show;
end;
procedure TFormHome.VideoStop;
begin
ThreadToSendTo := nil;
Timer1.Enabled := false;
FormStream.Hide;
end;
procedure TFormHome.Timer1Timer(Sender: TObject);
var
pic: TBitmap;
MemoryStream: TMemoryStream;
begin
if ThreadToSendTo = nil then
begin
Timer1.Enabled := False;
Exit;
end;
pic := FormStream.Image1.Picture.Bitmap;
try
MemoryStream := TMemoryStream.Create;
try
VideoGrabber.GetBitmap(pic);
pic.SaveToStream(MemoryStream);
try
ThreadToSendTo.Connection.WriteStream(MemoryStream, True, True);
except
ThreadToSendTo := nil;
Timer1.Enabled := False;
end;
finally
MemoryStream.Free;
end;
finally
FormStream.Image1.Picture := nil;
end;
end;
Client:
Uses
..., IdSync;
type
TLogNotify = class(TIdNotify)
protected
procedure DoNotify; override;
public
Msg: String;
end;
procedure TLogNotify.DoNotify;
begin
FormClient.LogMsg(Msg);
end;
procedure TFormClient.Button1Click(Sender: TObject);
begin
TCPClient.Connect;
end;
procedure TFormClient.Button2Click(Sender: TObject);
begin
try
TCPClient.WriteLn('videostop');
finally
TCPClient.Disconnect;
end;
end;
procedure TFormClient.TCPClientConnected(Sender: TObject);
var
pesan : string;
begin
with TLogNotify.Create do
begin
Msg := 'Connected to Server';
Notify;
end;
TCPClient.WriteLn('videostart');
pesan := TCPClient.ReadLn;
if pesan = 'send' then
TIdNotify.NotifyMethod(VideoStart);
end;
procedure TFormClient.TCPClientDisconnected(Sender: TObject);
begin
with TLogNotify.Create do
begin
Msg := 'Disconnected from Server';
Notify;
end;
TIdNotify.NotifyMethod(VideoStop);
end;
procedure TFormClient.LogMsg(const AMsg: string);
begin
IncomingMessages.Lines.Insert(0, AMsg);
end;
procedure TFormClient.VideoStart;
begin
Timer1.Enabled := true;
end;
procedure TFormClient.VideoStop;
begin
Timer1.Enabled := false;
Image1.Picture := nil;
end;
procedure TFormClient.Timer1Timer(Sender: TObject);
var
ReadStream : TMemoryStream;
begin
ReadStream := TMemoryStream.Create;
try
TCPClient.ReadStream(ReadStream, -1, False);
ReadStream.Position := 0;
Image1.Picture.Bitmap.LoadFromStream(ReadStream);
finally
ReadStream.Free;
end;
end;