C H A P T E R 1 2

Drag and Drop

Drag Feedback

Your application should provide drag feedback as soon as the user drags an item at least three pixels. If a user holds the mouse button down on an object or selected text, it should become draggable immediately and stay draggable as long as the mouse remains down. Typically, applications have to provide an image to drag and have to handle the receiver frame. In Aqua, dragged items are transparent.

Destination Feedback

If the user drags an item to a destination in your application, your application provides feedback that indicates whether it will accept that item. Destination feedback should not occur simply because your application is “drag-aware”; rather, it should depend on the destination’s ability to accept the type of data contained in the dragged item. For example, a text entry field that accepts only text should not be highlighted when the dragged item is a graphic.

The actual appearance of destination feedback depends on the type of destination. The Drag Manager provides some utilities for simple highlighting; if your application needs more complex highlighting, you must provide your own highlighting utilities.

Windows

The valid destination region of a document window is usually the window’s content area minus the title bar and areas used for controls (such as scroll bars, resize controls, tool palettes, rulers, and placards). When there are multiple destination regions within a window, only one destination region is highlighted at a time.

Apple Computer, Inc. June 2002

C H A P T E R 1 2

Drag and Drop

When the user drags an acceptable item from one destination region to another, your application highlights the destination region as soon as the pointer enters it, and removes the highlighting when the pointer leaves the region. You can use the Drag Manager to specify your destination regions.

If a drag-and-drop operation takes place entirely within one destination region (moving a document icon to a different location in the same folder window, for example), don’t highlight the destination region, to avoid distracting the user.

However, if the user drags an item completely out of a destination region and then drags the same item back to the same destination region, the destination region should be highlighted.

You can provide more specific destination feedback within a larger destination region. For example, when the user drags text from one document window to another, the inactive window should display an insertion point where the dragged text would go if the user releases the mouse button.

In many situations, highlighting a more narrowly defined area of a window is more appropriate than highlighting the entire content region; examples are spreadsheets, text boxes, fill-in forms, and panes. In these cases, the destination region must be tailored to more precisely indicate the specific destination.

Text

While the user is dragging an item to a text area, an insertion indicator (a vertical bar) should appear in the text where the dragged item would be inserted if the user releases the mouse button.

Multiple Dragged Items

If the user drags multiple items, the destination feedback should occur only if it can accept all of the dragged items. If the destination cannot accept all of the dragged items, the user’s attempt results in feedback as described in “Feedback for an Invalid Drop” (page 227).

When the destination can accept all of the dragged items, the destination should accept them in the order specified by the source. The source application should organize the dragged items in the order in which they were selected, except in two cases. If the dragged items come from ordered views (such as View by Date or an

224Destination Feedback

Apple Computer, Inc. June 2002