The LA Fox Developer Newsletter

September 1997

Drag and Drop (Con’t from page 1)

(default) and Automatic. There is less control over dragging

when in Automatic mode so we’ll leave the DragMode property

for all objects set to 0-Manual (the default).

There are three components for Drag-and-Drop:

1. Theform,

2.

The source list, and

3.

The target(s).

Each has methods or properties that need to be filled in to

make Drag-and-Drop work, and with a short description 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:

Can Targetlcon (enter DRAGPAGE.CUR for this Property;

CanSourcelcon (enter DRAGYES.CUR for this Property;

NoDroplcon (enter NODROP.CUR for this Property

DragThreshold (enter 8 for this Property);

MouseX (don’t enter anything now);

MouseY (don’t enter anything now)

The first three properties give us a convenient place to store

names of cursors; the DragThreshold number will tell us how far

the left-clicked mouse needs to move before we know the user

wants to Drag-and-Drop; and the MouseX and MouseY proper-

ties are just temporary places to put the mouse location

information when we need it.

The following code goes into the INIT method of the form:

use reports

public array aReports[reccount()]

x1

scan

this.lstSource.Additem(trim(reports.desc))

aReports[x]=trim(reports.filename)\

x=x+1

endscan

use

This code reads REPORT. DBF and populates the source

Listbox (lstSource) for us. It also populates the aReports array

with the corresponding names of report files for each report

description.

So that’s it for the form.. .six properties and some INIT code.

The Drag-and-Drop Source

The Drag-and-Drop source is the object “lstSource”, a ListBox

holding the descriptions of system reports. We need to modify

three methods in this object.

1.

The DragOver method should read:

LPARAMETERS oSource, nXCoord, nYCoord, nState

*

This sets cursor shape when leaving or entering..

do case

case nState = 0 && Entering list

oSource.Draglcon = this.parent.CanSourcelcon

case nState = I && Leaving the list

oSource. Draglcon = this.parent.NoDroplcon

endcase

Remember creating the CanSourcelcon property for the form?

This is where we use it. Same for NoDroplcon. This code here

changes the cursor as the user moves it out of the ListBox,

from an arrow with a box next to it to a cirle & slash cursor like

those on No Smoking signs.. Impressive stuff for so little work.

2. The MouseDown method should read:

LPARAMETERS nButton, nShift, nXCoord, nYCoord

this.parent.MouseX = nXcoord

this.parent.MouseY = nYcoord

Remember creating the Mousex and MouseY properties for the

form? We use those now to record the starting position of the

mouse when the left mouse button is first pressed.

3. The MouseMove property should read:

LPARAMETERS nButton, nShift, nXCoord, nYCoord

if nButton = I && Left Mouse Button

if abs(nXcoord-

thls.parent.MouseX)>this.parent.DragThreshold or;

abs(nYcoord-

this.parent.MouseY)>this.parent.DragThreshold

this.drag() && start dragging

endif

endif

Remember adding DragThreshold as a property for the Form?

Remember entering “8” in this property? This code enables

Dragging of the selected item from the source ListBox if the

user holds down the left mouse button and moves the pointer

more than 8 pixels. This gives users a little leeway before the

cursor changes, but you could set the DragThreshold property

to and number you wish.

So that’s it for the Source.. .only three methods and very little

code!

The Drag-and-Drop Target(s)

Targets are even easier.. .there are only two methods in each

target that need our attention.

1.

The DragOver method should look like this:

LPARAMETERS oSource, nXCoord, nYCoord, nState

*

This sets cursor shape when leaving or entering this

(Con't, page 4)

Page 3