IViewObject
The
IViewObject interface enables an object to display itself directly without passing a data
object to the caller. In addition, this interface can create and manage a
connection with an advise sink so the caller can be notified of changes in the view
object.
The caller can request specific representations and specific target devices.
For example, a caller can ask for either an object's content or an iconic
representation. Also, the caller can ask the object to compose a picture for a target
device that is independent of the drawing device context. As a result, the
picture can be composed for one target device and drawn on another device context.
For example, to provide a print preview operation, you can compose the drawing
for a printer target device but actually draw the representation on the
display.
The
IViewObject interface is similar to
IDataObject; except that
IViewObject places a representation of the data onto a device context while
IDataObject places the representation onto a transfer medium.
Unlike most other interfaces,
IViewObject cannot be marshaled to another process. This is because device contexts are
only effective in the context of one process.
When to Implement
Object handlers and in-process servers that manage their own presentations
implement
IViewObject for use by compound document containers. OLE provides an
IViewObject implementation for its default object handler's cache.
When to Use
You call
IViewObject from a container application if you need to draw a contained object on a
specific device context. For example, if you want to print the object to a printer,
you call the
Draw method in the
IViewObject interface.
Methods in VTable Order
IViewObject Methods
| Description
|
Draw
| Draws a representation of the object onto a device context.
|
GetColorSet
| Returns the logical palette the object uses for drawing.
|
Freeze
| Freezes the drawn representation of an object so it will not change until a
subsequent Unfreeze.
|
Unfreeze
| Unfreezes the drawn representation of an object.
|
SetAdvise
| Sets up a connection between the view object and an advise sink so that the
advise sink can receive notifications of changes in the view object.
|
GetAdvise
| Returns the information on the most recent SetAdvise.
|
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