ok... this is the original code I had after updating it to SL2
List<UIElement> elements = VisualTreeHelper
.FindElementsInHostCoordinates(e.GetPosition(null), this).ToList();
for (int i = 0; i < elements.Count; i++)
{
ListBox lb = elements[i] as ListBox;
if (lb != null)
{
....
}
}
then I changed it to this
ListBox lb = (from el in VisualTreeHelper
.FindElementsInHostCoordinates(e.GetPosition(null), this)
where el.GetType().Name == "ListBox"
select el).SingleOrDefault() as ListBox;
if (lb != null)
{
....
}
and now I change the first line to this...
ListBox lb = (from el in VisualTreeHelper
.FindElementsInHostCoordinates(e.GetPosition(null), this)
select el).Where(el => el.GetType().Name ==
"ListBox").SingleOrDefault() as ListBox;
if (lb != null)
{
....
}
so which is the best way and why do you think it?
.Where(el => el.GetType().Name == "ListBox")
is this better/going to cost more than the "for" loop...?
On Wed, Oct 22, 2008 at 12:27 PM, Jordan Knight
<[EMAIL PROTECTED]>wrote:
> +1
>
> As Jeffrey Richter says:
>
> Always take the least specific and return the most specific :)
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:
> [EMAIL PROTECTED] On Behalf Of ross jempson
> Sent: Wednesday, 22 October 2008 1:20 PM
> To: listserver@ozsilverlight.com
> Subject: Re: [OzSilverlight] Drop & Drag - DataGridRow
>
> this isn't really a c# list, but i will respond.
>
> ok, to be pedantic i think the only reason it works is because you are
> lucky the method you are calling is storing the the data internally as
> List<UIElement>, or something that can be cast to List<UIElement>.
>
> but you are programming against an interface, IEnumerable<UIElement>,
> and your code will break if the implementation of the method you are
> calling changes. And you may not have control over that.
>
> consider the console app below. the first cast works, iterating over
> the IEnumerable works in the second case, but the third causes a
> runtime error because the code has assumed it knows how the
> GetStringsFromQueue() method is storing the data internally.
>
> class Program
> {
> static void Main(string[] args)
> {
> // Works by luck
> ((List<string>)GetStringsFromList()).ForEach(i =>
> Console.WriteLine(i));
> Console.ReadKey();
>
>
> // Works as designed
> foreach (string s in GetStringsFromQueue())
> {
> Console.WriteLine(s);
> }
> Console.ReadKey();
>
> // Runtime error
> ((List<string>)GetStringsFromQueue()).ForEach(i =>
> Console.WriteLine(i));
> Console.ReadKey();
>
>
> }
>
> private static IEnumerable<string> GetStringsFromQueue()
> {
> System.Collections.Generic.Queue<string> ret = new
> Queue<string>();
>
> ret.Enqueue("D");
> ret.Enqueue("E");
> ret.Enqueue("F");
>
> return ret;
>
> }
>
> private static IEnumerable<string> GetStringsFromList()
> {
> List<string> ret = new List<string>();
>
> ret.Add("A");
> ret.Add("B");
> ret.Add("C");
>
> return ret;
> }
> }
>
>
>
>
>
> On Wed, Oct 22, 2008 at 10:52 AM, .net noobie <[EMAIL PROTECTED]>
> wrote:
> > no it works
> >
> > On Wed, Oct 22, 2008 at 10:15 AM, ross jempson <[EMAIL PROTECTED]>
> > wrote:
> >>
> >> Wouldn't this option you presented create a runtime cast error anyway?
> >>
> >> List<UIElement> elements =
> >>
> >>
> (List<UIElement>)VisualTreeHelper.FindElementsInHostCoordinates(e.GetPosition(null),this);
> >>
> >> Hence .ToList() is better I would suggest.
> >>
> >> Another thing to consider is whether you actually need a List<> which
> >> forces the list to be fully populated. Leaving it as an IEnumerable<>
> >> will be more effecient in some scenarios, as the datasource may be
> >> lazy loading.
> >>
> >>
> >> On Wed, Oct 22, 2008 at 2:26 AM, .net noobie <[EMAIL PROTECTED]>
> >> wrote:
> >> > Thanks, I found this link for a ListBox version
> >> > needed to update the .HitTest to SL2 and it works fine
> >> > I only wanted a single column, I used a DataGrid because I was being
> >> > lazy
> >> > and wanted to use the DataGrid Header, but I will just make that for a
> >> > ListBox :)
> >> > changed this line for SL2
> >> > List<UIElement> elements =
> >> > (List<UIElement>)this.HitTest(e.GetPosition(null));
> >> > to
> >> > List<UIElement> elements =
> >> >
> >> >
> (List<UIElement>)VisualTreeHelper.FindElementsInHostCoordinates(e.GetPosition(null),
> >> > this);
> >> >
> >> >
> >> >
> http://cid-71b364b59919d1e8.skydrive.live.com/self.aspx/Public/blog%20files/dragdrop|_updated.zip
> >> > which is the better way to do this line?
> >> > List<UIElement> elements =
> >> >
> >> >
> (List<UIElement>)VisualTreeHelper.FindElementsInHostCoordinates(e.GetPosition(null),
> >> > this);
> >> > or
> >> > List<UIElement> elements =
> >> > VisualTreeHelper.FindElementsInHostCoordinates(e.GetPosition(null),
> >> > this).ToList();
> >> > which one takes more work under the covers to make the conversion to a
> >> > list?
> >> >
> >> > On Tue, Oct 21, 2008 at 8:57 PM, Valentin Stoychev
> >> > <[EMAIL PROTECTED]> wrote:
> >> >>
> >> >> I hope you will not treat this as an advertisement.
> >> >>
> >> >> Take a look at this example from the Telerik QuickStart Application.
> >> >> http://demos.telerik.com/silverlight/#Examples/DragAndDrop/FirstLook
> >> >>
> >> >> It is using the Telerik Drag/Drop framework that do exactly what you
> >> >> need,
> >> >> but with listboxes. Modifying the sample a little bit will do the job
> >> >> for a
> >> >> DataGrid.
> >> >>
> >> >> Regards,
> >> >> Valentin Stoychev
> >> >> Telerik
> >> >>
> >> >> On Tue, Oct 21, 2008 at 1:05 PM, Stephen Price
> >> >> <[EMAIL PROTECTED]>
> >> >> wrote:
> >> >>>
> >> >>> I got drag and drop between listboxes working in a prototype I was
> >> >>> working on few months ago.
> >> >>> I used canvas's and a method that checked for a collision/overlap
> >> >>> between
> >> >>> the two elements when you did the drop.
> >> >>> Used the standard mouse approach of move events while button down to
> >> >>> animate the dragging around part. Had to clone the image element
> >> >>> myself as
> >> >>> no clone in Silverlight. I've since had an idea of another way to
> copy
> >> >>> the
> >> >>> image but haven't been back to test out my idea. (maybe using brush
> >> >>> source -
> >> >>> you know how you can have video brushes all pointing at same source?
> >> >>> wondering if that would work with an image brush).
> >> >>> hope that makes sense...
> >> >>> cheers,
> >> >>> Stephen
> >> >>>
> >> >>> On Tue, Oct 21, 2008 at 4:00 PM, .net noobie <
> [EMAIL PROTECTED]>
> >> >>> wrote:
> >> >>>>
> >> >>>> I would like to be able to Drop & Drag a DataGridRow from one
> >> >>>> DataGrid
> >> >>>> to another...?
> >> >>>> does anyone have any tips or links on how I would do this please?
> >> >>>>
> >> >>>> --
> >> >>>> .net noobie(tm)
> >> >>>>
> >> >>>> -------------------------------------------------------------------
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