In computer graphical user interface drag & drop
is the action of clicking on an object (virtual object on
the screen) and dragging itto different location (on screen)
The basic sequence involved in drag & drop is
Press and hold down the button on the mouse or the
other pointing device to “grab” the object.
Drag” the object/cursor/pointing device to
the desired location.
“Drop”the object by releasing the button.
A simple drag & drop sequence is given below.
Fig1 contains 2 columns: first column contains animal
names and second column contains small boxes where relevant
images are dropped.
Fig 1: Images before being dragged to the target
Drag and drop the relevant images
Fig2. Images after being dragged to the target
1.2. How Drag and Drop works
Drag and drop is actually the same as cutting and pasting
(or copying and pasting) using the mouse instead of keyboard.
In both cases you have source (where you are cutting or copying
from) and a target (where you are pasting to). During either
operation, a copy of the data is maintained in memory. Cut and
paste uses clipboard; drag and drop uses a data object, which
is in essence private clipboard.
1.3. Properties and methods of Drag & drop
Here is the sequence of events in drag and drop operation:
1. Dragging is initiated by calling DoDragDrop method
for source control.
The DoDragDrop method takes 2 parameters
Data, specifying the data to pass
Allowed effects, specifying which operations (copying
and/or moving) are allowed
2. A new data object is automatically created.
This in turn raises GiveFeedbackevent. In most
cases you do not need to worry about Givefeedback
event,but if you wanted to display a custom mouse pointer
during the drag, this is where you would add your code.
Any control with its AllowDropproperty is set
to true is potential drop target. AllowDrop property
can be set at design time or programmatically at Form Load
As the mouse passes over each control, the DragEnterevent
fro that control is raised. GetDatPresentmethod is
used to make sure that format of data is appropriate to
the target control and Effect property is used to
display the appropriate mouse pointer.
If the user releases the mouse button over a valid drop
target, the DragDrop event is raised. Code in the
DragDrop event handler extracts the data from the
DataObjectobject and displays it in the target control.
1.4. System Requirement
The example code given in the tutorial runs on any Windows
computer running windows7, XP, vista. Project is done in Visual
Basic. Net. VB programmers primarily intend the tutorial for
use, and you may be requiring VB.net software installed on your
computer to run the program.