TREESCRL Scrolls in a Tree Control During Drag-and-Drop (162159)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 2.1
- Microsoft Visual C++, 32-bit Editions 2.2
- Microsoft Visual C++, 32-bit Editions 4.0
- Microsoft Visual C++, 32-bit Editions 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition 4.2
- Microsoft Visual C++, 32-bit Professional Edition 4.2
This article was previously published under Q162159 SUMMARY A TreeView control is one capable of displaying items in a
tree-like hierarchical fashion. The control supports drag-and-drop. When an
item is dragged to the top or bottom of the control, the control does not
automatically scroll vertically. Treescrl.exe shows how to add
scrolling functionality to a tree control during drag-and-drop.
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MORE INFORMATION TREESCRL uses the CTreeView view class that encapsulates
the functionality of a view and a tree control. The sample's drag-and-drop
functionality is similar to the one demonstrated in CMNCTRLS, a sample shipped
with the Visual C++ product. When TREESCRL is built and run, an SDI window with
a CTreeView comes up. When you grab a tree control item (parent or child), and
drag it above/below the top/bottom of the view window, the tree control starts
scrolling upward/downward.
The idea behind TREESCRL is to install a
timer when a drag-and-drop operation starts. In the handler for the WM_TIMER
message, it is first determined if scrolling is needed. If it is, then the
appropriate scroll message is sent to the control. When the drag-and-drop
operation terminates, the timer is killed. The sample shows how to draw the
drag image and how to select the drop site during the dragging phase.
The tree control can scroll in different modes. During the drag
phase, when the mouse cursor is close to the top or the bottom border of the
view, scrolling is slow. The control scrolls at this slow speed when the
horizontal distance between the mouse and the corresponding view border
(top/bottom) is less than the width of a horizontal scrollbar. Scrolling speeds
up when the mouse is taken further away from either border.
SLOWSCROLL_FREQUENCY is a macro symbol in the view's .cpp file. This symbol
determines the relative speeds of normal and slow scrolling. Normal scrolling
occurs approximately every 75 milliseconds (the frequency of the timer). In the
sample, SLOWSCROLL_FREQUENCY is defined to be three (3), which means slow
scrolling is three times slower than normal scrolling. To change the slow
scrolling speed, modify this value to a positive integer.
| Modification Type: | Minor | Last Reviewed: | 8/5/2004 |
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| Keywords: | kbdownload kbcode kbfile kbinfo kbSample kbTreeView KbUIDesign KB162159 kbAudDeveloper |
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