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Last post Aug 26, 2010 04:05 AM by JoseHidalgo

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meykih

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Databinding on combobox - layout update

Nov 11, 2008 11:40 AM | LINK

I have a little problem with the combobox control: The binding of a list works absolutely well even if I change the list at runtime. My problem is that the length of the dropdown part does not change anymore after opening it for the first time. An example:

When the page is loaded the combobox contains four items. When I open it I see them all. After that I for example press a button and now the combobox contains seven items. But when I open it it I still see only the first four items and a scrollbar for the rest...

I already tried UpdateLayout but that didn't do it. Does anyone have an idea how to change the listlength at runtime everytime the number of items changes?
Thanks

Regards,
Maike Ohlig

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Ken Tucker

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Re: Databinding on combobox - layout update

Nov 11, 2008 12:05 PM | LINK
Set the combobox's MaxDropDownHeight
```
                <ComboBox x:Name="searchBox" Margin="10,10,10,10" Grid.Column="1" Grid.Row="0" Width="300" MaxDropDownHeight="150" >
```
Developer at Amovius onshore software solutions
Space Coast .Net User Group
meykih

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Re: Databinding on combobox - layout update

Nov 11, 2008 12:13 PM | LINK

Doesn't work. Still no size update after the first opening...

Regards,
Maike Ohlig

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IanBlackburn

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Re: Databinding on combobox - layout update

Nov 11, 2008 12:20 PM | LINK

ken tucker
Set the combobox's MaxDropDownHeight

Hi Ken,

Does that work for this scenario? It restricts the height, but only upto a maximum, and the initial height is set during the first binding.

Here we want the opposite - we want to expand the height of the DropDownList to fit all the added items in without using a scrollbar. MinDropDownHeight would seem to be the anser, but there is no such property!

I got this working by creating the whole thing in code like this, but it's not very satifactory:

    public partial class Page : UserControl
    {
        ObservableCollection people;
        ComboBox combo1;
        public Page()
        {
            InitializeComponent();
            people = new ObservableCollection();
            people.Add(new Person() { Id = 1, Name = "Fred" });
            people.Add(new Person() { Id = 2, Name = "John" });
            people.Add(new Person() { Id = 3, Name = "Paul" });
            people.Add(new Person() { Id = 4, Name = "Jane" });
            people.Add(new Person() { Id = 5, Name = "Julie" });
            CreateCombo();
            
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            people.Add(new Person() { Id = 6, Name = "Eileen" });
            LayoutRoot.Children.Remove(combo1);
            CreateCombo();
        }
        private void CreateCombo()
        {
            combo1 = new ComboBox();
            combo1.ItemsSource = people;
            combo1.DisplayMemberPath = "Name";
            LayoutRoot.Children.Add(combo1);
        }


    }

The combobox must be doing some work somwhere where it works out this height - we need to find out how to get it to do it again!

I'll have a look in reflector and see what I can find...

(If this has answered your question, "Mark as Answer" - many thanks)

Cheers

Ian Blackburn
SilverlightForBusiness.net

IanBlackburn

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Re: Databinding on combobox - layout update

Nov 11, 2008 12:37 PM | LINK
Ok here is the answer:
```
people.Add(new Person() { Id = 6, Name = "Eileen" });
            Rect r = new Rect();
            //rough calcuation follows!!
            r.Height = people.Count * 25;
            r.Width= combo1.ActualWidth;
            Combo2.Arrange(r);
```
The only thing left to do is work out the height of each row so you can calculate the correct Rect size.

Hope this helps.
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Ian Blackburn
SilverlightForBusiness.net
meykih

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Re: Databinding on combobox - layout update

Nov 11, 2008 12:47 PM | LINK

I'm really sorry but my combodropdown still keeps its length set at first opening...

Regards,
Maike Ohlig

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IanBlackburn

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Re: Databinding on combobox - layout update

Nov 11, 2008 01:15 PM | LINK

meykih
I'm really sorry but my combodropdown still keeps its length set at first opening...

Can you post the xaml and the code you are using so I can replicate it.

(If this has answered your question, "Mark as Answer" - many thanks)

Cheers

Ian Blackburn
SilverlightForBusiness.net
meykih

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Re: Databinding on combobox - layout update

Nov 11, 2008 01:38 PM | LINK

IanBlackburn

Can you post the xaml and the code you are using so I can replicate it.

Hi Ian,

unfortunately it's code written for my employer... And too complex to put it into a small anonymous application. So, I think I have to go on trying by myself, yes?

Regards,
Maike Ohlig

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IanBlackburn

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Re: Databinding on combobox - layout update

Nov 11, 2008 01:45 PM | LINK
Did you try increasing the value here:
```
r.Height = people.Count * 50;
```
(If this has answered your question, "Mark as Answer" - many thanks)

Cheers

Ian Blackburn
SilverlightForBusiness.net
meykih

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Re: Databinding on combobox - layout update

Nov 11, 2008 01:50 PM | LINK
IanBlackburn

Did you try increasing the value here:
```
r.Height = people.Count * 50;
```
I even tried a factor 100 and nothing happend. Also the other case that the second list is shorter than the first one makes no changes to the size. In that case I see some empty rows below the actual items. Absolutely no size update...
Regards,
Maike Ohlig

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