What is the easiest way to use a valueconverter with a listbox?
I'm setting the ItemSource to a List<> of objects at runtime, and it displays a textstring from the ToString() method. What I would like, though, is to pass the object through a valueconverter to get a completely different string value.
All the examples I have found makes a big deal of binding the list to something in xaml, and defining styles and templates to redesign the whole box, but I just want my values converted...
Use a data template with something like:
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter=....}" />
</...>
That's it. When you don't specify a path in your binding, it simply binds to the current object.
Related
I have this requirement, that I have a collection of items (ObservableCollection), but I only want to display the first item. The requirement comes from the fact that in most of the case, the collection only contains one item. And due to the space limit, even if there is more than one items in the collection, we'd like to display the number of the items, details of the first one (same presentation as prior situation) and a ... symbol to indicate to the user that there is more items. And when the mouse is over the UI element a popup will eventually display all items.
The first solution I can think of (please suggest others if they are better) is to bind to this collection (but not using an ItemsControl) and define a DataTemplateSelector derived class (which return either the DataTemplate to display the only one item, or the DateTemplate which has the ... and the popup for more details, based on the number of items in the collection) and use it as ContentTemplateSelector.
But now my question: how both of my DataTemplate would look like in XAML, so that they can display only the first item in the collection? Obviously I can't have a ItemsControl.
UPDATE:
Now I have managed to make it work and agree this question can be closed (I can't delete it anymore since there is already some answers).
I actually knew how to bind to one certain item in the collection, but this was not where I am confused. I felt I should use ContentControl as one answer suggests. But I thought since I need to bind to the whole collection (not to single indexed item), and use a DataTemplateSelector to select the proper DataTemplate based on the number of items in the collection. The code would look like this:
<ContentControl Content="{Binding MyCollection}"
ContentTemplateSelector="{StaticResource MyTemplateSelector}" />
And in MyTemplateSelector I wasn't sure how to use it since there is no reference to my collection because it is defined as resource and it doesn't have the information of MyCollection. However, it turned out to be very simple, the DataTemplate can refer to an indexed item without knowing the name or any other reference. Simply like this:
<DataTemplate>
<TextBlock Text="{Binding [0].PropertyName}" />
<DataTemplate />
To bind to just one item from a collection, you can use the following syntax:
{Binding Items[0]}
Or to bind to a property of a single item from the collection:
{Binding Items[0].Property}
You can find out more about property path syntax from the Binding.Path Property page at MSDN... from the linked page:
• Indexers of a property can be specified within square brackets following the property name where the indexer is applied. For instance, the clause Path=ShoppingCart[0] sets the binding to the index that corresponds to how your property's internal indexing handles the literal string "0". Multiple indexers are also supported.
Try this
<ContentControl Content="{Binding YourCollection[0]}">
<ContentControl.ContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"></TextBlock>
</DataTemplate>
</ContentControl.ContentTemplate>
</ContentControl>
Ok, late to the party but I thought I'd share my 2 cents anyway: I'd better go with a dumber (XAML-)view and a view-model closer to your presentation needs.
Translated: instead of mapping your existing view-model (or raw data) and its collection of items directly to the view, I suggest to map that to an appropriate view-model showing something like a YourItemViewModel FirstItem property and a bool HasMore property. That second view-model would be easily unit-testable to make sure it behaves propertly, and would be easily mapped to a view with less logic, so to avoid possible hard-to-test problems in view.
{Binding Items[0].SomeProperty}
{Binding [0].SomeProperty}
{Path=/SomeProperty}
I've got a Listpicker with a DataBinding on the Itemssource-Property. Binding works fine. Now I want to define a FallbackValue. My problem is, that the FallbackValue is interpreted as a list: {'S','t','a','n','d','a','r','d'}, not as a single item 'Standard'. I'm looking for a solution to solve this problem. Any idea?
<toolkit:ListPicker x:Name="listPicker" ExpansionMode="FullScreenOnly" ItemsSource="{Binding Profilelist, ElementName=userControl, FallbackValue='Standard'}" SelectedIndex="0" />
The fallback behaviour is correct as the target expects an array (and a string an usable as an array of chars). There is no easy way to specify an array for the fallback.
I would suggest binding to a ViewModel list, instead of directly to the other control, so you can specify whatever default you want in the list. It does mean an extra binding and a property on your ViewModel (or code-behind... yuk) but element binding is not designed to have a fallback array, only single values.
If you can provide more code/Xaml I will be able to be more specific.
This dialog makes no sense to me
http://img576.imageshack.us/img576/4223/50709706.gif
And I'm having trouble finding good tutorials on it. Most of the examples aren't detailed enough, or do stuff via code, but I'd like to take advantage of the IDE as much as possible.
Whats the difference between ItemsSource and DataContext?
I'd like to bind it to just a List for starters. I don't need SQL or databases or anything fancy. Where would I declare my list? In MainWindow.xaml.cs? How do I get it to appear in that dialog?
Think of "DataContext" as the default value for "Source" in a binding.
When you create a binding, you can specify the path and source, like this (I'll use TextBox as an example):
<TextBox Text="{Binding Path=Foo,Source={StaticResource Bar}}" />
So my TextBox.Text property is bound to a Foo property on an object called Bar (a resource somewhere in the application).
However, if you have a whole bunch of things that you want to bind to properties on Bar, it's easier to set Bar as the DataContext of the parent container. A Binding without a Source will just use the DataContext by default, and DataContext flows through to child controls from the parent. So:
<StackPanel DataContext="{StaticResource Bar}">
<TextBox Text="{Binding Path=Foo}" />
<TextBox Text="{Binding Path=Fizz}" />
<TextBox Text="{Binding Path=Buzz}" />
</StackPanel>
All of the TextBoxes are still binding to properties on Bar, but they're doing it without setting it as a Source explicitly.
So let's have another look at the dialog you posted. It's giving you several options for the "source" of the ItemsSource binding. When you choose "DataContext", you're telling Visual Studio that the ItemsControl doesn't need to know the source - it'll pick it up from the DataContext of the parent container (maybe even the Window itself).
If you chose one of the other options (ElementName, RelativeSource or StaticResource) then you'd be setting the binding's source explicitly for that ItemsControl.
Once you've told it that it's binding to the DataContext, you'll need to drop into the "Path" section of the dialog and tell it which property to bind the items of the control to. In the end, the markup would look something like this (assuming it's a ListBox):
<ListBox ItemsSource="{Binding Path=Foos}" />
So the items in the ListBox are coming from a property called "Foos", and that property is on an object that's set in the DataContext somewhere higher in the logical tree (perhaps on the Window itself).
You rarely need to use the data context of a control outside of the control. The most common use case for setting DataContext(DataContext = this;) is within UserControl's code-behind to make all controls within the UserControl to bind to the control's properties.
When you use a ListBox, setting ItemsSource is sufficient, unless you are doing something funky.
This is a pretty good walkthrough: http://windowsclient.net/learn/video.aspx?v=315275
Specifically, you need to set the DataContext first to tell it where to look for the ItemsSource. The easiest way is to set this on the Window through the XAML:
<Window.DataContext>
<controllers:DownloadManager />
</Window.DataContext>
I'm trying to databind to a listbox like so:
<ListBox x:Name="MyListBox" Margin="0,0,0,65">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource MyConverter}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
The reason I am binding to the whole object and not a property is because my converter will need multiple properties of the object to build the string that it returns.
This works and my string is returned. But then when I change the ObservableCollection that this is based on the value doesn't change on the screen. If I bind to just a single property and change it, then the value does change.
What can I do differently? I can't bind to a single property since I need the entire object in the converter... And the ConverterParameter is already being used.
Remember, if you bind to the "main" property and the value of the main property itself isn't changed, the binding will have no reason to refresh itself. It has no clue that your converter is actually based off of a sub-property. What you can do is use a MultiBinding where you bind not only the "main" property, but also a specific sub-property. This gives your IMultiValueConverter implementation access to the main data object, but because you're also binding to the sub-property that's changing, will also be refreshed when that sub-property's value changes.
You can try using a MultiBinding which I believe updates whenever any of its Bindings are triggered. You can also use an IMultiValueConverter or just take advantage of the StringFormat of the binding.
A templated control I'm working on uses a ValueConverter like so:
<ListBox>
<ListBox.Resources>
<Controls:CodeDescriptionValueConverter x:Key="CodeDescriptionValueConverter"/>
</ListBox.Resources>
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource CodeDescriptionValueConverter}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
This is the default look that I supply in generic.xaml. When I use this control I'll want to pass different format strings into the converter. Is there a way to make that happen without providing the full ControlTemplate?
My first thought was that I could use ConverterParameter with a TemplateBinding to a property on the control, but I discovered that ConverterParameters can't be bound to. Another option could be to get access to the control from the ConvertTo method, then pick off that property. I'm not sure how to do that. Any options that would eliminate the need to completely re-template the control each time I use it would be helpful (it's a lot of Xaml).
In these situations, I generally do one of two things:
1) Bind to an object that has access to both the property you want to bind to the format string. In the the converter you will then have access to both the property and the format string.
2) Add properties to your data object/viewmodel/etc for the format string and the formatted text. Then bind to the formatted text properties. Assuming that you are using INotifyPropertyChanged, keep in mind that you will need to fire the propertychanged event for the formatted text property whenever you change the text or format string properties