I tried your method and it failed to have any effect that I could see. I
read the source to the function that you were having me somewhat override
the behavior of, eventually gave up understanding that, and came up with my
own hacked solution.
protected override function collectionChangeHandler(event: Event): void {
var oldScrollPosition: Number = this.verticalScrollPosition;
super.collectionChangeHandler(event);
// My hopes is that by only restricting downward movements I'm avoiding
potential problems with the
// list shrinking and it trying to auto-scroll UP for me. I haven't seen
it scroll up in a case I didn't want it to.
if (oldScrollPosition < this.verticalScrollPosition) {
this.verticalScrollPosition = oldScrollPosition;
}
}
This has the unfortunate side effect of not following an item that the user
really has selected, but in this particular application that feature is
secondary to sitting and watching the top of the list, which is made very
difficult with the current behavior. I think that this could be extended to
incorporate both behaviors if I dug around in the documentation for enough
internal variables. Not sure what to do about multiple selection.
Alex, can you confirm if you saw the jumping behavior with no row selected
at all? If not, it may have been fixed as a side-effect of another fix in an
update, and this hack of mine would be entirely unnecessary.
Daniel
On 4/5/07, Daniel Grace <[EMAIL PROTECTED]> wrote:
"We do try to keep the selected item in view."
The thing is though that I don't have a selected item. Do you only see it
when there is a selected item? I will look at the variables/functions you've
pointed me at tomorrow. Thanks for the help and speedy replies. I see that
the good things I've heard about Adobe's treatment of Flex were spot on.
Daniel
On 4/5/07, Alex Harui <[EMAIL PROTECTED]> wrote:
>
> I ran the test case. I see it jump, and it should if you're sorted on
> the column. We do try to keep the selected item in view. I think I saw it
> not keep it in view once or twice so that might still be a bug, but would
> expect jumping if the sorted column data is being changed.
>
> We hit the lower-level scrollposition so that's why your handler didn't
> get called.
>
> One way to block it might be to subclass, overrride
> collectionChangeHandler, and on REFRESH, set anchorBookmark to null before
> calling super and restore it afterwards.
>
> -Alex
>
> ------------------------------
> *From:* [email protected] [mailto:[EMAIL PROTECTED] *On
> Behalf Of *Daniel Grace
> *Sent:* Thursday, April 05, 2007 3:32 PM
> *To:* [email protected]
> *Subject:* Re: [flexcoders] DataGrid Jumping
>
> After more fully evaluating the problem, the simple test case that I
> wrote DOES exhibit the behavior when I follow all requisite steps:
>
> 1) Load the flash
> 2) Sort by the only field
>
> The sorting appears to be necessary. It seems to me, from watching, that
> when the first row moves off of the screen, the viewport moves to keep the
> old first row to be the first row in the viewport. After that, that
> particular row is no longer followed, but it will jump subsequent times,
> perhaps to try and follow the new first-row, when it moves away from being
> the first row? Either way, with sorting on this example using all native
> Flex components jumps around like crazy.
>
> <?xml version="1.0" encoding="utf-8"?>
> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml "
> layout="absolute" applicationComplete="appComplete();">
> <mx:DataGrid dataProvider="{ac}" width="100%" height="100%">
> <mx:columns>
> <mx:DataGridColumn headerText="Testing" dataField="timer" />
>
> </mx:columns>
> </mx:DataGrid>
> <mx:Script>
> <![CDATA[
> import mx.utils.ObjectProxy;
> import mx.collections.ArrayCollection;
> import flash.utils.Timer;
> import mx.core.Application;
>
> public var t: Timer = new Timer(1000);
> [Bindable]
> public var ac: ArrayCollection = new ArrayCollection([
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> // Repeat enough times to make this take up more than one screen... or
> just shrink your window
> new ObjectProxy({'name': 'Test 1', 'timer': 0}),
> new ObjectProxy({'name': 'Test 1', 'timer': 0})]);
>
> private function appComplete(): void {
> this.t.addEventListener("timer", this.doTick);
> this.t.start();
> }
>
> private function doTick(e: Event): void {
> for (var i: Number = 0; i <
> Application.application.ac.length; i++) {
> Application.application.ac.getItemAt(i).timer += (
> Math.random() * 10) - 5;
> }
> }
> ]]>
> </mx:Script>
> </mx:Application>
>
> Daniel
>
> On 4/5/07, Daniel Grace <[EMAIL PROTECTED]> wrote:
> >
> > Just to repay the quick reply to my email, you should know that a very
> > quck test case failed to replicate the bug without the rest of my framework
> > involved. I have also noticed a few more things about this bug. First, it
> > only happens if I have a sorted field (I don't do any custom sorting, and it
> > happens at least with String sorting, which is the most common field anyone
> > sorts on in this application) and it mostly happens when the text I am
> > sorting on has changed somewhere (unfortunately, that's common enough that I
> > can't be sure that's part of the true cause). I don't have lines selected at
> > the time. I created a function to try and find the bug (in a DataGrid
> > subclass):
> >
> > public function set veriticalScrollPosition(n: Number):
> > void {
> > Application.application.logError("Setting scroll
> > position to " + n);
> > super.verticalScrollPosition = n;
> > }
> >
> > Note that this failed to ever run, even when I saw the bug happen. Are
> > there any other functions that could trap when this bug is rearing its head?
> > I like having the source to most/all of the framework for when something
> > like this happens, but there sure is a lot of code to try and understand.
> >
> > Daniel
> >
> > On 4/5/07, Alex Harui < [EMAIL PROTECTED]> wrote:
> > >
> > > I don't remember any bugs like that. Can you build a small test
> > > case that uses regular DataGrid?
> > >
> > > ------------------------------
> > > *From:* [email protected] [mailto:[EMAIL PROTECTED]
> > > *On Behalf Of *Daniel Grace
> > > *Sent:* Thursday, April 05, 2007 12:40 PM
> > > *To:* [email protected]
> > > *Subject:* [flexcoders] DataGrid Jumping
> > >
> > > I am using a DataGrid that is mostly stock (overrode
> > > drawRowBackground
> > > and set dataProvider. This particular datagrid has a lot of
> > > information in it that changes every second. That's all fine.
> > >
> > > If there is a vertical scroll bar (common) and I am scrolled to the
> > > top, with no rows selected, it will periodically jump down to what
> > > appears to be roughly the halfway point. This seems to happen when
> > > something changes (and happened a lot less frequently before I put
> > > the
> > > timers in). There is a chance that I have messed something up, but I
> > > doubt it. I know that it happened before I overrode set
> > > dataProvider.
> > >
> > > My real question is -- is this addressed in the hotfix? I don't see
> > > specific mentioning of it on
> > > http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=kb401224 ,
> > > though there are fixes in the datagrid. After seeing a few problem
> > > reports here I'm not overly eager to install the hotfix if it is not
> > > going to fix a problem that I am having (also, the page referenced
> > > suggests this strategy).
> > >
> > > Or, does anyone know what might be causing my scroll position to
> > > jump,
> > > without overriding any functions that would logically cause such a
> > > behavior?
> > >
> > > Daniel
> > >
> >
> >
>
>
