This 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.
At a Glance
| Header file: | Oleidl.h |
| Windows CE versions: | 2.0 and later |
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.
| Method | Description |
| IViewObject::Draw | Draws a representation of an object onto the specified device context. |
| IViewObject::Freeze | Freezes a certain aspect of the object’s presentation so that it does not change until the IViewObject::Unfreeze method is called. |
| IViewObject::GetAdvise | Retrieves the existing advisory connection on the object if there is one and returns the parameters used in the most recent call to the IViewObject::SetAdvise method. |
| IViewObject::GetColorSet | Returns the logical palette that the object uses for drawing in its IViewObject::Draw method with the corresponding parameters. |
| IViewObject::SetAdvise | Establishes a connection between the view object and an advise sink so that the advise sink can be notified about changes in the object’s view. |
| IViewObject::Unfreeze | Releases a previously frozen drawing. |