TUpDown bug

Posted on 2002-07-18
Last Modified: 2010-05-18
I've just discovered a strange bug in TUpDown (D5 Enterprise) -

Place a TUpDown and a two TEdits onto a form, set the TUpDown's Wrap property to true, and Associate it with Edit1. Add an OnClick event to show which button was clicked (up or down) -

procedure TForm1.UpDown1Click(Sender: TObject; Button: TUDBtnType);
  Edit2.Text :=   IntToStr(ord(Button));

At the wrap point (by default Min & Max should be 0 & 100 respectively) the Button value is reversed! When the value is 100, clicking the Prev button returns btNext, when the value is 0, clicking the Next button returns btPrev...

Anyone know of a fix?
Question by:isstorr
LVL 10

Expert Comment

by:János Szabó
ID: 7162099

this is the normal behavior of the control. You see in the Help the followings:


Specifies how the up-down control handles attempts to exceed the value of Max or Min.

property Wrap: Boolean;


Use Wrap to specify whether the up-down control treats the range determined by the Max and Min properties as a continuous loop. If Wrap is True, the value of Position becomes the value of the Min property when the user increments Position beyond the value of Max, and becomes the value of Max when the user decrements Position beyond the value of Min.

with best regards


Author Comment

ID: 7162110
Sounds like a bug to me... surely clicking the Prev button should always yield btPrev? The value wraps around correctly, it is just the reported button clicked which is wrong.
LVL 14

Expert Comment

ID: 7162203
No, it's correct behaviour. This makes sure that you can expect the value top have increased when you get a btNext event, or to have decreased when you get a btPrev even (even in the case of a wrap).
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Accepted Solution

Cynna earned 50 total points
ID: 7164188
The "fix" for this would be adding some code:

var LastPeaked: Boolean=TRUE; // Global var

//......your code

procedure TForm1.UpDown1Click(Sender: TObject; Button: TUDBtnType);
var Up: Boolean;
   if ord(Button)=0 then Up:=TRUE else Up:=FALSE;
   with UpDown1 do
        if (Position=Max) or (Position=Min) then begin
           if LastPeaked then Up:=not Up
                         else LastPeaked:=TRUE;
        else LastPeaked:=FALSE;
   // Up now containes pressed button:
   if Up then Edit2.Text :='Up' else Edit2.Text :='Down'


Author Comment

ID: 7164289
Thanks Cynna that works great :)

You have a point AvonWyss, its a sort of chicken & egg situation I guess. My argument was that clicking the up button should always yield an 'up button clicked' result, regardless of what happens to the actual value.
LVL 10

Expert Comment

by:János Szabó
ID: 7164814
Hi isstorr,

sorry for the misunderstand



Author Comment

ID: 7165086
np :)
thanks again for your input every1

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