Develop Reference

XAML ListView: header binding not working

I can't make the {Binding Title} in the HeaderTemplate appear.
This is the class connected to the BindingContext:
class SensorGroup
{
public string Title { get; set; }
public IList<Sensor> Sensors { get; set; }
}
XAML:
<ListView Header=""
ItemsSource="{Binding Sensors}">
<ListView.HeaderTemplate>
<DataTemplate>
<Grid>
<Label Text="{Binding Title}"/>
</Grid>
</DataTemplate>
</ListView.HeaderTemplate>
<ListView.ItemTemplate>
...
</ListView>
If I replace it with <Label Text="Some static text"/>, the text appears.
I have found this related question, which links to this other question. But I could not make it work. I tried:
<ContentPage.Resources>
<Label x:Key="MyTitle"
Binding="{Title}"/>
</ContentPage.Resources>
...
<Grid>
<StaticResource ResourceKey="MyTitle"/>
</Grid>
It gives me an error saying that the binding with Title cannot be found.

Sounds you like just need to do:
<ListView Header="{Binding .}"
ItemsSource="{Binding Sensors}">
That is if your ContentPage's BindingContext is set to the SensorGroup class.
The above is telling the ListView.Header to be bound to what ever the ContentPage.BindingContext is set to. That means that the ListView.HeaderTemplate controls will also use what ever ContentPage.BindingContext is set to.
Let me know if that does not make any sense.

How can I best display this nested collection? (Can you tell me why my code isn't working?)

Can you tell me why this code isn't working?
I have a viewmodel with an observablecollection of searchresults which has an observablecollection of resultproperties. I cannot seem to display the nested collection of result properties like I want.
Here are the objects (abstracted for readability):
class ViewModel
{
public ObservableCollection<SearchResults<TDomain>> SearchResults { get; set; }
}
class SearchResults<TDomain>
{
public TDomain Result { get; set; }
public ObservableCollection<ResultProperty> ResultProperties { get; set; }
}
class ResultProperty
{
public string PropertyValue { get; set; }
}
Here is the xaml I cannot get to work. The DataContext is set to the ViewModel:
<StackPanel>
<ItemsControl ItemsSource={Binding SearchResults}>
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text={Binding Result.Id}/>
<StackPanel Orientation="Horizontal">
<ItemsControl ItemsSource={Binding ResultProperties}>
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding PropertyValue}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<TextBlock Text="PLACEHOLDER /////"/>
</StackPanel>
The outcome I am looking for is something like this:
[Stack panel to keep things orderly]
1
property1property2property3...
2
property1property2property3...
3
property1property2property3...
PLACEHOLDER /////
The results I am getting are these
[Stack panel to keep things orderly]
1
2
3
PLACEHOLDER /////
In otherwords, the binding isn't picking up the string. I have verified that the collections are populating like expected. But I can't get the xaml to work.
**ADDITION INFORMATION
Ok, so I tried some of the solutions, but they aren't working so I am going to add more details because maybe I am missing something about how the collections are getting updated.
The viewmodel has a button on it called "Search" which uses an ICommand that calls a the view model's TrySearch method which is below:
public void TrySearch()
{
var results = _model.GetAll();
foreach(var result in results)
this.SearchResults.Add(new SearchResults<TDomain>(result));
}
Could there be a reason this doesn't work because of the way the collection is updated? SearchResults is a dependency property (I know I know, it should be INPC, but its not, its dependency), but the other collections are not. Could this be a problem?

I would create the data templates as resources and refer to them elsewhere in the XAML. For example:
<Window ....>
<Window.Resources>
<DataTemplate x:Key="SearchResultTemplate" TargetType="SearchResults">
<TextBlock Text={Binding PropertyValue}"
</DataTemplate>
<DataTemplate x:Key="ViewModelTemplate" TartgetType="ViewModel">
<StackPanel>
<TextBlock Text={Binding Result.Id}/>
<StackPanel Orientation="Horizontal">
<ItemsControl ItemsSource={Binding ResultProperties} ItemTemplate="{StaticResource SearchResultTemplate}" />
</StackPanel>
</StackPanel
</DataTemplate>
</Window.Resources>
<StackPanel>
<ItemsControl ItemsSource={Binding SearchResults} ItemTemplate="{StaticResource ViewModelTemplate}" />
</Window>
I'm not sure, but I think that the bindings you're using are telling the XAML parser to look for properties of the ViewModel class called ResultProperties and PropertyValue. The XAML parser doesn't see that they're properties of the object bound to that instance of the collection. Splitting it up like this should make it plain that the properties belong to the instance that the template is being applied to.

Your code is somehow correct but according to what you want it has a flow. The StackPanel has to be the ItemsPanel. Change it like this:
<StackPanel>
<ItemsControl ItemsSource="{Binding SearchResults}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Result.Id}"/>
<ItemsControl ItemsSource="{Binding ResultProperties}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" IsItemsHost="True"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding PropertyValue}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<TextBlock Text="PLACEHOLDER /////"/>
</StackPanel>

The answer is that my SearchResults class was not hooked up properly. I made it a dependency object with dependency properties and it works fine. I am assuming that would translate similarly if it was INotifyPropertyChanged. Thank you for the responses.

WPF Binding to parent ItemsControl from inside of child ItemsControl data template

I need to be able to bind to a parent ItemsControl's properties from inside of a child ItemsControl data template:
<ItemsControl ItemsSource="{Binding Path=MyParentCollection, UpdateSourceTrigger=PropertyChanged}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ItemsControl ItemsSource="{Binding Path=MySubCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=MyParentCollection.Value, UpdateSourceTrigger=PropertyChanged}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Let's assume that MyParentCollection (the outer collection) is of the following type:
public class MyObject
{
public String Value { get; set; }
public List<MyChildObject> MySubCollection { get; set;
}
And let's assume that MyChildObject from the above class is of the following type:
public class MyChildObject
{
public String Name { get; set; }
}
How can I bind to MyParentCollection.Value from inside of the inner data template? I can't really use a FindAncestor by type because they both all levels use the same types. I thought maybe I could put a name on the outer collection and use an ElementName tag in the inner binding, but that still couldn't resolve the property.
Any thoughts?

saving the parent item in the tag of the child itemscontrol could work
<DataTemplate>
<ItemsControl ItemsSource="{Binding Path=MySubCollection}" Tag="{Binding .}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Tag.Value, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>
its not tested but give you a hint in the right direction :)

Binding for Tag, as suggested in the other answer, is not required. All data can be obtained from DataContext of ItemControl (and this markup Tag="{Binding}" just copies DataContext into Tag property, which is redundant).
<ItemsControl ItemsSource="{Binding Path=MyParentCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ItemsControl ItemsSource="{Binding Path=MySubCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=DataContext.Value, RelativeSource={RelativeSource AncestorType=ItemsControl}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>

Nested databinding with WPF and C#

I'm trying to make a budget program. Where I need to have groupboxes with a list of textblocks inside.
<ItemsControl DataContext="{Binding}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<GroupBox Header="{Binding}">
<ItemsControl DataContext="{Binding}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Text}" />
<TextBlock Text="{Binding Value}" />
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</GroupBox>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
I need somehow to databind a list (perhaps?) with groupboxes so I'd create a list of group boxes, with some lines inside that would be a text with a currency value. So that I could create a group called "Apartment", with two lines "Rent $3000" and "Maintenance $150". Then I could have a second group called "Car" with lines "Insurance", "Loan" and "Maintenance" for instance.
But how would I databind this? And how would I need in C# to perform this. I'm at a loss.

Building off of Jay's comment, you would want to create a Hierarchical data model. Note I have left implementing INotifyPropertyChanged on the properties to you
public class BudgetLineItem : INotifyPropertyChanged
{
public string Name { get; set; }
public decimal Cost { get; set; }
}
public class BudgetGroup : INotifyPropertyChanged
{
public string GroupName { get; set; }
public ObservableCollection<BudgetLineItem> LineItems { get; set; }
}
public class BudgetViewModel : INotifyPropertyChanged
{
public ObservableCollection<BudgetGroup> BudgetGroups { get; set; }
}
Then your data-template would look like this:
<ItemsControl DataContext="{Binding ViewModel}"
ItemsSource="{Binding BudgetGroups}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<GroupBox Header="{Binding GroupName}">
<ItemsControl ItemsSource="{Binding LineItems}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}" />
<TextBlock Text="{Binding Cost}" />
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</GroupBox>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>

I could be off base here, but it sounds like you want to change the DataTemplate based on the type of object that is being bound from a list of heterogeneous objects.
If that's the case, you want to look into DataTemplateSelectors or create DataTemplates for each of the types you want to support in the list.
For example, for an Apartment you might have:
<DataTemplate DataType="local:ApartmentBudget">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Text}" />
<TextBlock Text="{Binding Value}" />
</StackPanel>
</DataTemplate>
a Car may look like:
<DataTemplate DataType="local:CarBudget">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Insurance}" />
<TextBlock Text="{Binding Loan}" />
<TextBlock Text="{Binding Maintenance}" />
</StackPanel>
</DataTemplate>
Then your ItemsControl can be set like:
<ItemsControl ItemSource="{Binding BudgetItems}">
The correct DataTemplate will be picked based on the data type. You can have even more control by creating a custom DataTemplateSelector.
See https://msdn.microsoft.com/en-us/library/ms742521(v=vs.100).aspx for more information.

How to achieve hierarchical data binding?

Learning WPF here and I'm trying to get my head around hierarchical data binding.
This is my situation:
public class A
{
public int Id { ... }
public IEnumerable<B> Children { ... }
}
public class B
{
public string SomeValue { ... }
}
I want to use a ItemsControl to display a collection of A and for each occurance of A I want an inner ItemsControl to display A.Children.
I thought this would do the trick but, apparently, I have much to learn yet...
<ItemsControl x:Name="icCollectionOfAs" ItemsSource="{Binding}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid Width="auto" Height="auto">
<TextBlock Text="{Binding Id}" />
<ItemsControl ItemsSource="{Binding Children}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding SomeValue}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Then, in code-behind...
icCollectionOfAs.ItemsSource = createSomeAsWithChildBsInThem();
The result of all this is nothing gets shown. Why?
Thanks

You should not specify the ItemsSource both in XAML (ItemsSource="{Binding}") and code behind (icCollectionOfAs.ItemsSource = createSomeAsWithChildBsInThem();) the XAML might have been called later.
The rest seems fine to me except that the TextBlock for the ID will probably be hidden behind the ItemsControl for the children as you use a Grid without rows or columns rather than a StackPanel.