我需要扩展TFileStream,以便它可以处理不是来自0偏移量的文件,而是来自用户定义的偏移量.我的意思是它必须将用户定义的偏移解释为流开始.我的代码是：
type
TSuFileStream = class(TFileStream)
protected
FOffset : int64;
procedure SetOffset(Offset : int64);
procedure SetSize(NewSize: Longint); override;
procedure SetSize(const NewSize: Int64); override;
public
constructor Create(const AFileName: string; Mode: Word); overload;
constructor Create(const AFileName: string; Mode: Word; Rights: Cardinal); overload;
function Seek(Offset: Longint; Origin: Word): Longint; override;
function Seek(const Offset: Int64; Origin: TSeekOrigin): Int64; override;
property Offset : int64 read FOffset write SetOffset;
end;
...
constructor TSuFileStream.Create(const AFileName: string; Mode: Word);
begin
inherited Create(AFileName,Mode);
FOffset := 0;
end;
constructor TSuFileStream.Create(const AFileName: string; Mode: Word; Rights: Cardinal);
begin
inherited Create(AFileName,Mode,Rights);
FOffset := 0;
end;
procedure TSuFileStream.SetOffset(Offset : int64);
begin
FOffset := Offset;
inherited Seek(FOffset,soBeginning);
end;
procedure TSuFileStream.SetSize(NewSize: Longint);
begin
inherited SetSize(FOffset + NewSize);
end;
procedure TSuFileStream.SetSize(const NewSize: Int64);
begin
inherited SetSize(FOffset + NewSize);
end;
function TSuFileStream.Seek(Offset: Longint; Origin: Word): Longint;
begin
Result := Seek(Int64(Offset),TSeekOrigin(Origin));
end;
function TSuFileStream.Seek(const Offset: Int64; Origin: TSeekOrigin): Int64;
begin
case Origin of
soBeginning: Result := inherited Seek(FOffset + Offset,soBeginning) - FOffset;
soCurrent: Result := inherited Seek(Offset,soCurrent) - FOffset;
soEnd: Result := inherited Seek(Offset,soEnd) - FOffset;
end;
end;
但它不起作用.问题在于寻求功能,但我不知道为什么.当我将这样的流传递给第三方组件时,它仅在TSuFileStream.Offset：= 0时起作用;
解决方法
使用
TGpStreamWindow,可在
my web和
Google Code获得.
用法：
var
offsetStream: TGpStreamWindow;
begin
offsetStream := TGpStreamWindow.Create(originalStream,initialOffset,originalStream.Size - 1);
try
DoSomethingWith(offsetStream);
offsetStream.SetWindow(anotherInitialOffset,originalStream.Size - 1);
DoSomethingElseWith(offsetStream);
finally FreeAndNil(offsetStream); end;
end;