How to provide file drag-and-drop functionality in a Visual C# application (307966)

SUMMARY

The step-by-step procedure that is outlined in this article demonstrates how to provide file drag-and-drop functionality in a Visual C# application. A ListBox control is used as the destination of the file drag-and-drop procedure.

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Requirements

This list outlines the recommended hardware, software, network infrastructure, and service packs that you need:

• Visual C# .NET or Visual C# 2005

This article assumes that you are familiar with the following topics:

• Windows Forms ListBox control
• Windows Forms event handling

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Steps to Build the Sample

The ListBox control provides two drag-and-drop events that you need to handle: DragEnter and DragDrop. The DragEnter event occurs when you drag an object within the bounds of the control and is used to determine whether the object that is being dragged is one that you want to allow to be dropped on the control. You handle this event for cases in which a file or files are dragged to the control. This allows the appropriate icon to be displayed when the object is dragged over the control, depending on the object that is being dragged. The DragDrop event occurs when the object that is being dragged has been released on the control. You handle this event to retrieve the object. The Data object is used to retrieve the data.

The Data object's GetData method returns an array of strings that contain the full path names of the files that were dragged to the ListBox control. You can use this file path information to perform whatever operations are needed on the files. For example, you can use classes in the System.IO namespace to open and read the files, move the files, or copy the files to a new location. In this example, you just add the full path to the files that are dragged to the ListBox control.

To provide file drag-and-drop functionality in a Visual C# application, follow these steps:

1. Create a new Windows Forms application in Visual C# .NET or Visual C# 2005. Form1 is created by default.
   
   Note The code should be changed in Visual Studio 2005. When you create a Windows Forms project, Visual C# adds one form to the project by default. This form is named Form1. The two files that represent the form are named Form1.cs and Form1.designer.cs. You write your code in Form1.cs. The Designer.cs file is where the Windows Forms Designer writes the code that implements all the actions that you performed by adding controls. For more information about the Windows Forms Designer in Visual C# 2005, visit the following Microsoft Web site:

   http://msdn2.microsoft.com/en-us/library/ms173077.aspx

2. Use the toolbox to add a ListBox control to Form1.
3. In the Properties window, change the AllowDrop property of the ListBox control to True to allow objects to be dragged onto the control.
4. In Solution Explorer, right-click Form1, and then click View Code.
5. To handle the DragEnter event, add the following method below the code section that the Windows Form Designer generates in the Form1 class:

   private void listBox1_DragEnter(object sender, System.Windows.Forms.DragEventArgs e)
   {
   	if(e.Data.GetDataPresent(DataFormats.FileDrop))
   		e.Effect = DragDropEffects.All;
   	else
   		e.Effect = DragDropEffects.None;
   }
   					

6. To handle the DragDrop event, add the following method to the Form1 class immediately following the method that you added in step 5:

   private void listBox1_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
   {
   	string[] s = (string[]) e.Data.GetData(DataFormats.FileDrop, false);
   	int i;
   	for(i = 0; i < s.Length; i++)
   		listBox1.Items.Add(s[i]);
   }
   					

7. To associate the two event handlers with the control events, add the following code in the InitializeComponent method of Form1. Be sure to add the code after ListBox1 has been instantiated:

   this.listBox1.DragDrop += new
              System.Windows.Forms.DragEventHandler(this.listBox1_DragDrop);
   this.listBox1.DragEnter += new
              System.Windows.Forms.DragEventHandler(this.listBox1_DragEnter);
   
   					

8. Build and run the project.
9. Drag one or more files from either the desktop or another folder to the ListBox control. Note that the full path of the files is added to the ListBox control.

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