怎样获取内存？

Question

//下载
procedure DownFile;
begin
  //....
  DownMemory(Stream, ASize); //下载Stream
  SendMessage(Handle, WM_DOWN_MSG, Integer(Stream.Memory), ASize);
end;
//接受数据
procedure GetDownMsg(var Msg: TMessage);
var
  Stream: TMemoryStream;
  ASize: Int64;
begin
  Stream := TMemoryStream.Create;
  try
    //Stream.Memory := DWORD(Msg.WParam); //这个地方这么做？必须用CopyMemory吗?能不能直接指针赋值就行了？
    //ASize := Int64(Msg.LParam);
    
    //...
    _FileStream.Position := _FileStream.Size;
    FileStream.CopyFrom(Stream, Stream.Size);
  finally
    FreeAndNil(Stream);
  end;  
end

Answer 1

可以这样试一下（没测试）：TMyMemoryStream = class(TMemoryStream) 
end;procedure GetDownMsg(var Msg: TMessage);
var
  Stream: TMemoryStream;
  ASize: Int64;
begin
  Stream := TMemoryStream.Create;
  try
    TMyMemoryStream(Stream).SetPointer(DWORD(Msg.WParam), Msg.LParam);
    //Stream.Memory := DWORD(Msg.WParam); //这个地方这么做？必须用CopyMemory吗?能不能直接指针赋值就行了？
    //ASize := Int64(Msg.LParam);
    
    //...
    _FileStream.Position := _FileStream.Size;
    FileStream.CopyFrom(Stream, Stream.Size);
  finally
    FreeAndNil(Stream);
  end;  
end

Answer 2

DWORD(Msg.WParam)应该改为Pointer(Msg.WParam)

Answer 3

Stream.ReadBuffer(Pointer(Msg.WParam)^, Msg.LParam);

Answer 4

你看下VCL的源代码就知道了procedure TMemoryStream.LoadFromStream(Stream: TStream);
var
  Count: Longint;
begin
  Stream.Position := 0;
  Count := Stream.Size;
  SetSize(Count);
  if Count <> 0 then Stream.ReadBuffer(FMemory^, Count);
end;

Answer 5

提示一下，我不知道发送过来的内存是怎么分配和释放的，但是在释放Stream前应加一句：
  finally  TMyMemoryStream(Stream).SetPointer(nil, 0);  FreeAndNil(Stream);
  end; 

Answer 6

写错了
应该是
Stream.WriteBuffer(Pointer(Msg.WParam)^, Msg.LParam); 才是写到Stream

Answer 7

简单测试了下var
  T1, T2: TMemoryStream;
begin
  T1 := TMemoryStream.Create;
  T1.LoadFromFile('C:\新建 文本文档 (3).txt');  T2 := TMemoryStream.Create;
  T2.WriteBuffer(T1.Memory^, T1.Size);  
  T2.SaveToFile('C:\新建 文本文档 (4).txt');  T1.Free;
  T2.Free;
end;

Answer 8

拷贝之前要做 FileStream.Position := 0;