How to use DragAndDrop function in Unity3D custom editor. This is just handle when user drag anything outside to THIS EditorWindow only.

using UnityEngine; using UnityEditor; using System.Collections; using System.Collections.Generic;

public class DragAndDropEditorWindow : EditorWindow { [MenuItem("Window/Drag And Drop")] public static void Open() { GetWindow(false, "DragDrop", true); }

private void OnGUI()
{
	if (Event.current.type == EventType.DragUpdated)
	{
		DragAndDrop.visualMode = DragAndDropVisualMode.Copy;
		Event.current.Use();
	}
	else if (Event.current.type == EventType.DragPerform)
	{
		// To consume drag data.
		DragAndDrop.AcceptDrag();

		// GameObjects from hierarchy.
		if (DragAndDrop.paths.Length == 0 && DragAndDrop.objectReferences.Length > 0)
		{
			Debug.Log("GameObject");
			foreach (Object obj in DragAndDrop.objectReferences)
			{
				Debug.Log("- " + obj);
			}
		}
		// Object outside project. It mays from File Explorer (Finder in OSX).
		else if (DragAndDrop.paths.Length > 0 && DragAndDrop.objectReferences.Length == 0)
		{
			Debug.Log("File");
			foreach (string path in DragAndDrop.paths)
			{
				Debug.Log("- " + path);
			}
		}
		// Unity Assets including folder.
		else if (DragAndDrop.paths.Length == DragAndDrop.objectReferences.Length)
		{
			Debug.Log("UnityAsset");
			for (int i = 0; i < DragAndDrop.objectReferences.Length; i++)
			{
				Object obj = DragAndDrop.objectReferences[i];
				string path = DragAndDrop.paths[i];
				Debug.Log(obj.GetType().Name);

				// Folder.
				if (obj is DefaultAsset)
				{
					Debug.Log(path);
				}
				// C# or JavaScript.
				else if (obj is MonoScript)
				{
					Debug.Log(path + "\n" + obj);
				}
				else if (obj is Texture2D)
				{
					
				}

			}
		}
		// Log to make sure we cover all cases.
		else
		{
			Debug.Log("Out of reach");
			Debug.Log("Paths:");
			foreach (string path in DragAndDrop.paths)
			{
				Debug.Log("- " + path);
			}

			Debug.Log("ObjectReferences:");
			foreach (Object obj in DragAndDrop.objectReferences)
			{
				Debug.Log("- " + obj);
			}
		}
	}
}

}