Delphi: why TStreamAdapter is not suitable for IStream-based virtual files?
Hello,
One delphi programmer wrote me that he tried to create a IStream-based virtual file using a TStreamAdapter. But it doesn’t work. Why?
The reason is quite simple: TStreamAdapter doesn’t provide a correct implementation of IStream.Clone. Check Classes.pas:
function TStreamAdapter.Clone(out stm: IStream): HResult; begin Result := E_NOTIMPL; end;
IStream.Clone is important method, BoxedApp SDK uses it. But TStreamAdapter just returns E_NOTIMPL. OK, but what’s the solution?
The solution is to create a new class derived from TStreamAdapter and implement IStream.Clone.
For example, if you need a TStreamAdapter based on TFileStream, the implementation would be the following:
type
TCloneSA = class(TStreamAdapter)
public
Path: String;
public
function Clone(out stm: IStream): HResult; override; stdcall;
destructor Destroy; override;
end;
{ TCloneSA }
function TCloneSA.Clone(out stm: IStream): HResult;
var
FS: TFileStream;
S: TCloneSA;
begin
FS := TFileStream.Create(Path, fmOpenReadWrite or fmShareDenyNone);
S := TCloneSA.Create(FS, soOwned);
S.Path := Path;
result := S.QueryInterface(IStream, stm);
end;
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