本文整理自网络，侵删。
方法一:
Delphi 的 TBitmap 类可以方便地操作流, 如果能让 TGPImage 和 TBitmap 沟通起来就好了;
TGPImage 有一个子类 TGPBitmap 可以和 TBitmap 沟通... ok 了!
代码如下:
uses GDIPOBJ, GDIPAPI;
procedure TForm1.FormPaint(Sender: TObject);
const
ImgPath = 'c:\temp\test.bmp';
var
img: TGPImage;
bit: TBitmap;
g: TGPGraphics;
begin
bit := TBitmap.Create;
bit.LoadFromFile(ImgPath); {因为 TBitmap 操作流特别方便, 这里就没有演示}
img := TGPBitmap.Create(bit.Handle, bit.Palette);
g := TGPGraphics.Create(Canvas.Handle);
g.DrawImage(img, 0, 0);
g.Free;
bit.Free;
img.Free;
end;
方法二:
TGPImage 需要的是 IStream 而非 TStream, 直接给它一个 IStream 参数不就完了?
那怎么实现 IStream 接口呢? Classes 单元下有一个 TStreamAdapter 类就是专门实现 IStream 接口的.
uses GDIPOBJ, GDIPAPI;
procedure TForm1.FormPaint(Sender: TObject);
const
ImgPath = 'c:\temp\test.bmp';
var
img: TGPImage;
MemStream: TMemoryStream;
MyIStream: TStreamAdapter;
g: TGPGraphics;
begin
MemStream := TMemoryStream.Create;
MemStream.LoadFromFile(ImgPath);
MyIStream := TStreamAdapter.Create(MemStream);
img := TGPImage.Create(MyIStream);
g := TGPGraphics.Create(Canvas.Handle);
g.DrawImage(img, 0, 0);
g.Free;
img.Free;
MemStream.Free;
MyIStream := nil; {注意这里}
end;
注意 TStreamAdapter 的本质还是个接口, 只能 MyIStream := nil; 而不能 MyIStream.free;
如果这样写可能会容易理解一些, 不过要多 uses 一个 ActiveX 单元:
uses GDIPOBJ, GDIPAPI, ActiveX;
procedure TForm1.FormPaint(Sender: TObject);
const
ImgPath = 'c:\temp\test.bmp';
var
img: TGPImage;
MemStream: TMemoryStream;
MyIStream: IStream; {这里和上面不同}
g: TGPGraphics;
begin
MemStream := TMemoryStream.Create;
MemStream.LoadFromFile(ImgPath);
MyIStream := TStreamAdapter.Create(MemStream);
img := TGPImage.Create(MyIStream);
g := TGPGraphics.Create(Canvas.Handle);
g.DrawImage(img, 0, 0);
g.Free;
img.Free;
MemStream.Free;
MyIStream := nil;
end;
TStreamAdapter.Create 方法还有一个 TStreamOwnership 类型的默认参数, 默认值是 soReference;
如果改为 soOwned, 那连 MyIStream := nil; 也不需要了; 因为和 MyIStream 关联的对象会一同释放它.
uses GDIPOBJ, GDIPAPI;
procedure TForm1.FormPaint(Sender: TObject);
const
ImgPath = 'c:\temp\test.bmp';
var
img: TGPImage;
MemStream: TMemoryStream;
MyIStream: TStreamAdapter;
g: TGPGraphics;
begin
MemStream := TMemoryStream.Create;
MemStream.LoadFromFile(ImgPath);
MyIStream := TStreamAdapter.Create(MemStream, soOwned);
img := TGPImage.Create(MyIStream);
g := TGPGraphics.Create(Canvas.Handle);
g.DrawImage(img, 0, 0);
g.Free;
img.Free;
MemStream.Free;
// MyIStream := nil; {此时如果有这句会出错}
end;
来源：https://www.ablanxue.com/prone_6918_1.html
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