Inside Macintosh: Programmer's Guide to MacApp / Part 2 - Working With MacApp

Chapter 28 - Working With Drag and Drop

Overview

A MacApp application can drag and drop data within a view, between views, and between itself and other applications that support drag and drop of similar data types. MacApp's drag-and-drop support relies on the Macintosh Drag Manager. The Drag Manager is integrated into System 7.5 and later versions of the Macintosh Operating System. Releases of System 7 before version 7.5 require the addition of the Macintosh Drag and Drop extension.

A global TDragDropSession object manages communication with the Drag Manager during drag-and-drop operations. A view that supports dropping registers with its window, and the window registers with the global drag session object.

MacApp's TView class contains fields and methods that provide the building blocks for MacApp's drag-and-drop support. Several subclasses of TView support drag and drop for the data types they display:

• TEditText. You can drag selected text to another location within a TEditText view, or to another view or application that accepts text. You can drag text to create a text-clipping file on the desktop or drag text to the Trash to delete the text. A TEditText view can accept a drop that contains text data only.

  Note that MacApp "floats" a TDialogTEView object (see page 247) over a TEditText or a TNumberText view to perform data entry. It is really the TDialogTEView view that handles dragging and dropping.

• TTextListView. You can drag selected text from a TTextListView object to another view or application that accepts text, or to the desktop to create a text-clipping file. A TTextListView view cannot accept dragged data. (Two parent classes of TTextListView, the TTextGridView and TGridView classes, contain most of the drag-and-drop support.)
• TNumberText. Dragging and dropping for a TNumberText view is the same as for a TEditText view, except that a TNumberText view expects dropped text data to be numeric.
• TPicture. You can drag a selected picture from a TPicture view to another TPicture view, to another view that accepts 'PICT' data, or to another application that accepts 'PICT' data. You can drag a selected picture to create a picture-clipping file on the desktop, or drag a picture to the Trash to delete it. A TPicture view can accept a drop that contains 'PICT' data only.

  To see picture dragging in action, open two "Views by Template" views in the DemoDialogs application and try dragging a picture between them, or to the Scrapbook, desktop, or Trash. You can also drop pictures from the Scrapbook or picture clippings from the desktop onto the TPicture view.

• TStaticText. You can drag text from a TStaticText view to any destination that accepts text data. A TStaticText view does not normally accept drops.
• TTEview, TDialogTEView. The TTEView class is MacApp's specialized text-editing class. The TDialogTEView class is a subclass of TTEView that "floats" over a TEditText or TNumberText view within a dialog view to perform data entry. For objects based on these view classes, you can drag selected text within the view, or to another view or application that accepts text data. You can drag text to create a text-clipping file on the desktop or drag text to the Trash to delete the text. A TTEView or TDialogTEView view can accept a drop that contains text data only.

Your application must enable dragging or dropping for these views as it does for view subclasses you define. For more information, see "Recipe--Turning on Drag-and-Drop Support for a View," beginning on page 610.