The LA Fox Developer Newsletter

June 1995

Drag-and-Drop for Dummies

by David A. Greene, MA [Productive Solutions]

Our job as software developers is to build applica-

tions that are useable; not applications that we think

are useable, but applications that really are useable

by normal people. This involves knowing all the tools

available to us, how they work, and when to use

them. Microsoft has built so much into Visual

FoxPro that it will be years before any one of us

conquers everything this language has to offer, so

this article came about as a way to share a few

shortcuts about a tool that only a few of us have

implemented in the past.

I had my initial doubts about using drag-and-drop. It

was never clear to me why this was invented when

so many other controls are adequate, but after using

it in a few applications it became dear that users

exert more control over the computing environment

when they can both select an item and the action to

be taken using that item. There are subtle user

benefits, to be sure, but drag-and-drop is now state

of the art and our clients (and superiors) are simply

going to expect it.

The Scenario

A System Administrator (with some FoxPro training)

can add, delete, or modify reports (.FRX/.FRT) for a

particular system. There is no telling how many

reports may be in the system at a given time, and

users must be able to select whether a report is sent

to the screen or to the printer.

Two tables will be used for this demonstration - a

Reports table with two fields for report Descriptions

and for report FileNames, and an Employee table -

plagiarized from the Tasmanian Traders demo that

comes with VFP.

In the form to the right, users are presented with the

ListBox containing the report descriptions, two .BMP

pictures as drop targets, and an “OK” button to close

the form.

Building Drag-and-Drop

Microsoft gives us two ways to use Drag-and-Drop:

Manual (default) and Automatic. There is less

control over dragging when in Automatic mode so

we’ll ignore it for now and go with what works best...

There are three components for Drag-and-Drop: the

form, the source list , and the target(s) . Each has

methods or properties that need to be filled in to

make Drag-and-Drop work, and with a short descnp-

tion for each property or method, it should be easy to

apply these concepts to any application.

The Form Holding Drag-and-Drop Objects

Use the New Property.. option from the Form menu

to add the following PROPERTIES to the form:

CanTargetIcon

(enterC:\VFP\SAMPLES\GRAPHlCS\CURSORS~

BULLSEYE.CUR for this Property);

CanSourcelcon

(enter C:~VFP~SAMPLES\GRAPHlCS\CURSORS\

DRAGMOVE.CUR for this Propertyo;

NoDroplcon

(enter C:\VFP\SAMPLES\GRAPHICS\CURSORS\

NODROPOI .CUR for this Property);

DragThreshold

(enter 8 for this Property);

MouseX

(don’t enter anything now);

MouseY

(don’t enter anything now)

(Con't, page 5)

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