Direct Manipulation
A clipboard is a system-wide place for users to store data temporarily. The clipboard enables your user to move data within a single application or to exchange data among applications. Typically, a user selects data in the application using the mouse or keyboard, then initiates a cut or copy operation on the selected data. The clipboard can hold an entire object or part of that object, and it can hold any kind of object. For example, the clipboard can hold a single line of text or an entire database, a single line segment or an entire graphic.
When the user selects the paste operation, the data is transferred to the application from the clipboard.
| Note: | Only a single item of data can be stored in the clipboard at a time. Therefore, do not use the clipboard to store data unless a user requests it because you can overlay the user's data stored there. This is important: the user must always control access to the clipboard. |
While you can only store a single item of data in the clipboard, you can store this item in multiple formats. This allows an application to choose the format it supports that gives it the most information about the data. For example, a graphics application might copy a picture into the clipboard as both a metafile and a bitmap. This allows applications that support both metafiles and bitmaps to retrieve the picture as a metafile if it needs to modify the picture or as a bitmap if it only needs to display the picture.
IClipboard predefines several system clipboard formats. In addition, any application can create and register additional private formats.
Before you can write any data to, or read any data from, the clipboard, you must first open it. Only a single application at a time can open the clipboard. If an application tries to open the clipboard but another application already has it open, it waits until the clipboard is available. The default behavior of the clipboard classes minimizes the time the clipboard is open.
If you use the default behavior of IClipboard, the clipboard functions that require an open clipboard open it when needed and close it when finished. You turn off the default behavior of IClipboard when you explicitly open the clipboard by calling IClipboard::open. If you open the clipboard in this manner, functions in IClipboard will not close the clipboard when complete. If you explicitly open the clipboard, you must close the clipboard by calling IClipboard::close. You can turn off the default behavior of IClipboard to place different formats of your data on the clipboard without opening and closing it to write each format.
All clipboard operations must be associated with a window. You provide thiswindow on the IClipboard constructor. If necessary, IClipboard makes this window the owner of the clipboard. The clipboard owner is the window responsible for the data put on the clipboard. It is also the window that the operating system sends messages to for events relating to the clipboard. The IClipboard object establishes this window as the system clipboard owner when you call IClipboard::empty. If you call IClipboard::owner before calling empty, your window will not be returned because it is not yet the system clipboard owner.
The clipboard classes support an advanced concept called delayed rendering. Delayed rendering allows you to wait until another application requests the data before you put the data on the clipboard. You activate delayed rendering by supplying 0 for the data when you call the clipboard functions to place data on the clipboard.
You process clipboard events by creating and attaching an IClipboardHandler object to your clipboard owner window. In particular, if you use delayed rendering, you must attach an IClipboardHandler object to your clipboard's window (the owner window). The window dispatcher calls this handler when a request is made to the clipboard for data that has not been placed there yet.
Because the clipboard should only be kept open for a short time, create IClipboard objects as temporary objects with a short lifetime. This helps ensure that the clipboard is only open for the time necessary.
The IClipboard destructor always closes the clipboard if it is still open.
Adding Clipboard Support
Using Default Direct Manipulation
Enabling Direct
Manipulation
Adding Images
to Drag Items
