The Clipboard: 3 Using The Clipboard

GEOS SDK TechDocs

2 Transfer Data Structures

4 Using Quick-Transfer

ClipboardQueryItem(), ClipboardRegisterItem(), ClipboardDoneWithItem()

To use the Clipboard, your application must have an Edit menu (or a GenEditControl object) and an object which can implement the Cut, Copy, and Paste operations. This object is often the application's Process object or some other coordinating object. This object must be able to do each of the things in the following list:

• Register with the Clipboard
  In a multitasking, multithreaded system, another application could change the Clipboard's contents. By registering with the Clipboard on application startup, the object will receive notification whenever the Clipboard's contents are changed (including when your application perpetrates the change). Registration is normally accomplished via the ClipboardAddToNotificationList() routine. The GCN notification list GCNSLT_TRANSFER_NOTIFICATION is used.Objects on this list can intercept MSG_META_CLIPBOARD_NOTIFY_NORMAL_TRANSFER_ITEM_CHANGED and MSG_META_CLIPBOARD_NOTIFY_TRANSFER_ITEM_FREED .
• Maintain the Edit Menu
  In order to provide the user with the Cut , Copy , and Paste features, your application must have an Edit menu. Most programmers will simply include a GenEditControl object to create and maintain the Edit menu. Your clipboard-management object must update the triggers properly whenever the contents of the Clipboard are changed.
• Handle MSG_META_CLIPBOARD_COPY, MSG_META_CLIPBOARD_CUT
When the user issues a Cut or Copy order, the object must put the proper data into the Clipboard Transfer VM File.
• Handle MSG_META_CLIPBOARD_PASTE
When the user issues a Paste order, the object must query the Clipboard to ensure a proper format is available and then copy the information from the Clipboard.
• Check out when shutting down
  Each object that registers with the Clipboard must unregister when shutting down. Otherwise, the UI might try to send notification to a defunct object or process, resulting in unpredictable behavior.

Because the Clipboard is constantly in use by many different threads, you must always gain exclusive access to the transfer VM file when you want to use it. After you're done with the transfer file, you should relinquish exclusive access so other threads can continue to use it.

For operations that involve changing the transfer item (cut and copy, for example), you must register your new transfer item with ClipboardRegisterItem() , which also allows other threads to use the file. For operations that involve looking at but not changing the transfer item, you should use ClipboardQueryItem() . Since you have no changes to register, you must later use ClipboardDoneWithItem() to give up your exclusive access to the transfer VM file.

Registering with the Clipboard

Managing the Edit Menu

The GenEditControl

Handling Cut and Copy

Handling Paste

Unregistering with the Clipboard

Implementing Undo

Transfer File Information

Undoing a Clipboard Change

GEOS SDK TechDocs

2 Transfer Data Structures

4 Using Quick-Transfer