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Enable Your Windows Forms Applications to Drag-and-Drop Data Objects

This article demonstrates how to import files from the Windows shell and how to enhance some UI controls to make them accept input via drag-and-drop. Notable examples are the TextBox and the PictureBox controls.


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rag-and-drop doesn't fulfill requirements, but it contributes to making your application appear more professional and easy to use. In Windows Forms applications, drag-and-drop operations consist mostly of handling a series of events. By accomplishing a few mandatory steps and working with the information available in the event arguments, you can easily facilitate dragging and dropping files, text, and any other sort of serializable data objects. This article demonstrates how to import files from the Windows shell and how to enhance some UI controls to make them accept input via drag-and-drop. Notable examples are the TextBox and the PictureBox controls.
Fast Facts
To make a control or a form into a valid target for drag-and-drop operations, you must toggle on the AllowDrop Boolean property. In addition to this unavoidable first step, you must write at least a couple of event handlers, DragOver and DragDrop, to receive data.
Drag-and-drop is one of those programming features rarely listed in the user requirements document because it is perceived as secondary and minor. Sure, drag-and-drop doesn't make your application run faster, nor does it add anything to the core business of the application. Drag-and-drop is not the solution to any core business issues and doesn't add any new functionality to the application. Yet drag-and-drop is a feature that, if missing, users promptly miss and are quick to add to the wish list for the next upgrade.
The first step to enable drag-and-drop in a form or control is setting the AllowDrop property to True.
As a matter of fact, drag-and-drop greatly simplifies how people use virtually any application. It makes transferring data from one control to the next, and from and to other applications and to the Windows shell itself, into a straightforward activity. Drag-and-drop has existed for a long time in Windows and had its first fully message-based SDK available with Windows for Workgroups in an earlier software era.

The advent of OLE made the drag-and-drop transition from messages to functions and generalized the format of the data being moved. Implementing drag-and-drop, though, remained a sort of nightmare for most programmers. Things were much easier for Visual Basic developers and you'll still find that model at the root of the .NET Framework support for drag-and-drop.



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