JVCL Help:TJvDBImage
JVCL Help: TJvDBImage Class
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TJvDBImage
TJvDynControlJVCLDBImage
run\JvDBImage.pas
Summary
This component is a TDBImage replacement that supports other image formats than bitmap, a limitation of TDBImage since D1.
Pascal
run\JvDBImage.pas
TJvDBImage = class(TDBImage);
Description
- JVCLInfo
IMAGE FORMATS: The implementation is simple: Just register image signatures with RegisterGraphicSignature procedure and the component takes care of the correct instantiation of the TGraphic object. The signatures register at unit's initialization are: BMP, WMF, EMF, ICO, JPG. If you got some other image library (such as GIF, PCX, TIFF, ANI or PNG), just register the signature: RegisterGraphicSignature(<string value>, <offset>, <class>)
or RegisterGraphicSignature([<byte values>], <offset>, <class>)
This means: When <string value> (or byte values) found at <offset> the graphic class to use is <class>.
For example (actual code of the initialization section): RegisterGraphicSignature([$D7, $CD], 0, TMetafile); // WMF
RegisterGraphicSignature([0, 1], 0, TMetafile); // EMF
RegisterGraphicSignature('JFIF', 6, TJPEGImage);
You can also unregister signature. IF you want use TGIFImage instead of TJvGIFImage, you can unregister with: UnregisterGraphicSignature('GIF', 0);
or just UnregisterGraphicSignature(TJvGIFImage); // must add JvGIF unit in uses clause
then: RegisterGraphicSignature('GIF', 0, TGIFImage); // must add GIFImage to uses clause
If you don't like the signature registration there is a new event called OnGetGraphicClass. The event gets the following parameters: Sender: TObject;
Stream: TMemoryStream;
var GraphicClass: TGraphicClass)
The memory stream containing the blob data is sent in Stream to allow the user to inspect the contents and figure out which graphic class is.
If the component can't find the graphic class and the user doesn't provide it in the OnGetGraphicClass event no graphic object is created, the default behavior is used (Picture.Assign(Field)). This might raise an exception ('Bitmap image is not valid').
The graphic class to be used must implement LoadFromStream and SaveToStream methods in order to work properly.
SUPPORT FOR TDBCtrlGrid: You can safely put a TJvDBImage in TDBCtrlGrid.
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