In the Universal Windows Platform API, how do I use x:Bind inside of a User Control (intended to be the layout for a GridView's ItemTemplate) to bind to instance properties of a GridView's ItemSource?
Background
I'm trying to re-create the layout found in Windows 10 stock apps like Sports, News, Money, etc.
I'm using a two GridViews for the main area of the app; one for "featured articles" (2 large photos w/ headlines) and one for all the other articles (smaller photos w/ headlines).
I'm able to bind to a data source that I supply in the code behind (a List where NewsItem is a POCO with a Image and Headline property) Here's the pertinent parts of the MainPage.xaml:
<Page ...
xmlns:data="using:NewsApp.Models" />
....
<GridView Name="FeaturedItems" Grid.Row="0">
<GridView.ItemTemplate>
<DataTemplate x:DataType="data:NewsItem">
<Grid Name="mainPanel" HorizontalAlignment="Stretch" Width="500" >
<Image Source="{x:Bind Image}" HorizontalAlignment="Stretch" />
<TextBlock Text="{x:Bind Headline}" />
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
....
The Image and Headline bind just fine (even though they've not been styled correctly). However, instead I think I need to bind to a User Control to get the styling options I want, control over resizing esp. when using Visual State Triggers and to simplify the XAML in general (at least, this was the technique suggested to me.)
So, I added a new User Control to the project (FeaturedItemControl.xaml), and copied in the DataTemplate's child Grid:
<UserControl ... >
<Grid Name="mainPanel" HorizontalAlignment="Stretch" Width="500" >
<Image Source="{x:Bind Image}" HorizontalAlignment="Stretch" />
<TextBlock Text="{x:Bind Headline}" />
</Grid>
</UserControl>
And then back in the MainPage.xaml, I change the DataTemplate to reference the new FeaturedItemControl:
<GridView Name="FeaturedItems" Grid.Row="0">
<GridView.ItemTemplate>
<DataTemplate x:DataType="data:NewsItem">
<local:FeaturedItemControl HorizontalAlignment="Stretch" VerticalAlignment="Stretch" />
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
However, I get the error message for both Image and Headline properties: Invalid binding path 'Headline': Property 'Headline' can't be found on type 'FeaturedItemControl'.
I've tried a few things but am flailing just throwing code at the problem without understanding what I'm doing. Any help would be greatly appreciated.
Thank you for your kind attention.
Using Depechie's answer, I formulated this little cheat cheat for posterity:
Do note that you MUST use this technique to utilize the VisualStateManager with items inside your data bound controls' (GridView, ListView) data templates.
1) Create a User Control.
2) Cut the content of the DataTemplate in your page and paste it into the User Control replacing the template's Grid.
3) Reference the User Control from inside the Data Template:
4) Modify the contents of the User Control changing x:Bind statements to utilize object.property notation:
<UserControl>
<StackPanel>
<Image Source="{x:Bind NewsItem.LeadPhoto}" />
<TextBlock Text="{x:Bind NewsItem.Headline}" />
<TextBlock Text="{x:Bind NewsItem.Subhead}" />
</StackPanel>
</UserControl>
5) Add this in the User Control's Code Behind:
public Models.NewsItem NewsItem { get { return this.DataContext as Models.NewsItem; } }
public ContactTemplate()
{
this.InitializeComponent();
this.DataContextChanged += (s, e) => Bindings.Update();
}
Well it's possible to use x:Bind in user controls, but you'll need to add some extra code behind.
I encountered the same problem in my project, you can see the result here : https://github.com/AppCreativity/Kliva/tree/master/src/Kliva/Controls
So what you need to do is, create a property in the code behind of your user control that points to the correct DataContext.
If you do that, you can use properties of that DataContext in the xaml of your control: for example:
Do note that in the constructor of your control you do need to add: DataContextChanged += (sender, args) => this.Bindings.Update(); because the datacontext will change depending on the page where your control is used!
Then on the page where you are placing this control, you'll also need to do the same to enable the x:bind to work.
You'll see this in my example on the MainPage.DeviceFamily-Mobile.xaml and MainPage.xaml.cs files.
Hope this helps.
x:Bind isn't really hierarchical like Binding/DataContext is. Additionally when you're not directly inside a DataTemplate (such as inside your user control) the object that x:Bind tries to use is 'this' rather than 'this.DataContext'. My current line of thinking on how to solve this sort of issue is to try not to use UserControls anywhere. Instead preferring DataTemplates contained within a ResourceDictionary. There are some pretty strong caveats to this approach though, you will for example crash the xaml compiler if you use x:Bind inside a data template that was created from the ResourceDictionary item template (add new item). you can find a pretty complete example here https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/XamlBind its important to note in the sample where they show the ResourceDictionary being used that its not actually just a ResourceDictionary.xaml its also a ResourceDictionary.xaml.cs (this is where the generated code from x:Bind ends up)
Another option is to add Headline and Image as properties on your user control and x:Bind them from the template, then inside the user control x:Bind as you are currently doing, but now the x:Bind generated path 'this.Headline' will exist. Unfortunately the order things are actually bound means that the x:Bind's you have inside your user control will have to be OneWay rather than the default OneTime. this is because x:Bind OneTime does the bind inside the InitializeComponent call, and any set of properties/DataContext stuff doesn't get done until after that has already run.
So to sum this up, you have two options, use data templates everywhere, or bind to properties that are directly on the user control.
Related
I'm trying to implement a tab control, where each item comes from an ICollectionView of my viewmodel. Each tab page, for the items from the ICollectionView will be the same. However, I would like there to be an extra tab page for configuration options.
So an example tab header 'screenshot' might be:
tabA | tabB | tabC | config
on another instance, it could be
tabA | config
or
config
I can define the header for each item using ItemTemplateSelectors, and the content using the ContentTemplateSelectors. So that bit should be okay.
I'm having trouble with adding the config page item since I do not know where to add it. I thought I could set the tab's ItemsSource to be a CompositeCollection, where the final item is the config page object. I have failed to achieve this.
In the following example, I can view the tab headers being populated correctly according to the designer sample data which I have set up - I have not yet added the config page.
<controls:MetroTabControl ItemsSource="{Binding View}">
<controls:MetroTabControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Value.siteDisplayName}" />
</DataTemplate>
</controls:MetroTabControl.ItemTemplate>
<controls:MetroTabControl.ContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding Value.siteComment}"/>
</DataTemplate>
</controls:MetroTabControl.ContentTemplate>
</controls:MetroTabControl>
As you see, I have set the ItemsSource to be {Binding View}. This "View" comes from my ViewModel and is an ICollectionView.
Ideally i'd be able to do some magic like:
<controls:MetroTabControl>
<controls:MetroTabControl.ItemsSource>
<CompositeCollection>
<CollectionContainer Collection="{Binding View}"/>
<SomeConfigPageObject/>
</CompositeCollection>
</controls:MetroTabControl.ItemsSource>
...snip...
</controls:MetroTabControl>
But the problem is that when I do the above, the designer preview of the control acts as if there are no items in the ItemsSource.
For reference, each item in the {Binding View} is a object which contains a Value property, the value property containing an object that contains, in this example, a siteDisplayName and siteComment.
For reference, the DataContext for the tab is defined the dockpanel that contains it, as follows.
<DockPanel DataContext="{Binding Source={StaticResource Configurator}}"
d:DataContext="{d:DesignInstance cfuid:ConfigSiteVMSampleData, IsDesignTimeCreatable=true}"
LastChildFill="True">
For reference, the Configurator is my viewmodel and is instantiated in the xaml as:
<UserControl.Resources>
<ResourceDictionary>
...snip...
<cfvmc:ConfigSiteVM x:Key="Configurator" />
...snip...
So, the actual question would be:
How do I add my "config page" at the end of the tab control? Preferably via using the above-hoped method of adding an extra config-page object on the CompositeCollection; however if this is not possible [1] i'm open for suggestions.
[1] I think it doesn't work because the {Binding View} is an ICollectionView and the CompositeCollection requires a "collection" and doesn't accept a "view"
Thank you.
Peter.
I decided to do it through code behind. This means that I do lose my ability to use the design-time data to preview my UI; but it works at run time.
So, in the xaml I have.
<controls:MetroTabControl Grid.Column="0" Grid.ColumnSpan="2"
Grid.Row="0" Grid.RowSpan="2"
ItemsSource="{Binding ElementName=ucMe, Path=TabSitesCollection}">
Where ucMe is the UserControl and TabSitesCollection is a
protected CollectionViewSource m_TabSitesCollectionViewSource;
protected CompositeCollection m_TabSitesComposites;
public ICollectionView TabSitesCollection
{
get { return m_TabSitesCollectionViewSource.View; }
}
That gets initialised in the constructor as follows
public ConfigSiteView()
{
m_TabSitesComposites = new CompositeCollection();
m_TabSitesCollectionViewSource = new CollectionViewSource();
m_TabSitesCollectionViewSource.Source = m_TabSitesComposites;
InitializeComponent();
}
Then, on the Loaded event I can do
m_TabSitesComposites.Add(new CollectionContainer() { Collection = GetModel.View });
m_TabSitesComposites.Add(new TabItem() { Header = "hi" });
m_TabSitesComposites.Add(new TabItem() { Header = "ho" });
This results in almost my desired UI
I now simply need to spiff up my settings tab item and i'm done.
For reference, the xaml designer does not have any preview data - Unless I change the xaml so that the preview loads up (which then breaks the actual execution)
It would have been nice to have it both work while running, and on preview, but I haven't figured out how to do that, and it's not a current priority.
I want to change my content off an AppBar dynamicly whith this code:
<Page.Resources>
<local:AppBarSelector x:Key="myAppBarSelector"/>
</Page.Resources>
<Page.BottomAppBar>
<AppBar>
<ContentControl Content="{Binding SelectedItem, ElementName=listBox}" ContentTemplateSelector="{StaticResource myAppBarSelector}">
<ContentControl.Resources>
<DataTemplate x:Key="1">
<TextBlock Text="Hallo Welt 1" Foreground="White" />
</DataTemplate>
<DataTemplate x:Key="2">
<TextBlock Text="Hallo Welt 2" Foreground="White" />
</DataTemplate>
</ContentControl.Resources>
</ContentControl>
</AppBar>
</Page.BottomAppBar>
And this is my Code behind:
public class AppBarSelector : DataTemplateSelector
{
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
Debug.WriteLine((string)item);
if (item == null) return base.SelectTemplateCore(item, container);
var contentControl = (ContentControl)container;
var templateKey = (string)item;
return (DataTemplate)contentControl.Resources[templateKey];
}
}
But this method is nerver called.Even the Debug.WriteLine function. Where is my mistake?
Just after some comments here...
(note: this is a bit general but I can't be more specific w/o some more code to reflect the issues)
This should work 'as is' - I don't see any problems that would produce that (I check with similar example fast and it works well with .ItemsSource = new List<string>{...}.
So that's not the culprit - but it doesn't hurt what I suggested - make a proper MVVM binding to properties, make the list ObservableCollection<> - and also it's always recommended to have a more higher-level objects (instead of just string) as your items (helps in many cases with binding with similar issues - that object implements INotifyPropertyChanged etc. - and you bind to a 'property' there, not the entire object).
The other error suggests some issues as well.
And lastly to bind two contentControls together - you don't normally need events as such. You can use Triggers from the style or XAML directly - but most of the time just bind both to a property in the view-model - and handle the 'change' in your property 'setter'.
You should put up a small primer that repeats this - who knows it might help you realize what you're doing wrong.
I am styling the ListPicker with a DataTemplate. All the examples I have read assume that the ListItems are bound complex objects and so can refer to properties on the objects using the usual Binding Property syntax. e.g.
this.myListPicker.Items.Add(new Profile() { Name = "Joe",
Occupation="Button pusher" });
and in the XAML,
<DataTemplate>
<StackPanel>
<TextBox Text="{Binding Name}" />
<TextBox Text="{Binding Occupation}" />
</StackPanel>
</DataTemplate>
However my ListPickers are bound to a List of simple strings and there does not seem to be a property on the string that actually refers to the string.
How do I get a handle to the string inside the DataTemplate so that I can assign them to a e.g. TextBox in the template?
In the example code you show, you do actually have a "complex" object, a Profile, and the binding you specify should work.
If you really just have strings as the items, then the binding in your ItemTemplate would look like:
<TextBox Text="{Binding }" />
The relevant detail is that all ItemsControls (and ListPicker seems to be one) set the DataContext of the view of each item to the item. The binding syntax, above, means "bind to the source itself", and, unless otherwise specified (like with Source or RelativeSource, etc.), the source of any binding is the DataContext.
MSDN has more details here.
I Have a ListBox and I am defining its ItemsTemplate using a custom control. I want the control to be displayed in different ways depending on the state of cetain properties of the object. How can I access the item that the ListBox.ItemTemplate is bound to?
<ListBox>
<ListBox.ItemTemplate>
<DataTemplate>
<custom:MyControl />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
With in the code of the custom control how would I do something like:
if((this.DataContext as SomeObject).CollectionProperty.Count() > 0)
DoAction();
I was accessing dataContext in the constructor and it was null. I accessed it in the this.Loaded event and it worked fine.
I have a windows phone 7 app with some xaml that looks like:
<Grid x:Name="ContentGrid" Grid.Row="1">
<ItemsControl x:Name="MyView" ItemTemplate="{StaticResource MyInner}"/>
</Grid>
The item template here looks like:
<DataTemplate x:Key="MyInner">
<ItemsControl ItemsSource="{Binding}" ItemTemplate="{StaticResource MyInner_Item}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</DataTemplate>
And finally, the MyInner_Item template looks like:
<DataTemplate x:Key="MyInner_Item">
<Button x:Name="MyButton">
<Button.Template>
<ControlTemplate>
<Border HorizontalAlignment="Center" VerticalAlignment="Center" x:Name="myborder">
<Image Source="{Binding Path=ImageUri}" Width="{Binding Path=Width}" Height="{Binding Path=Height}" Stretch="Fill" />
</Border>
</ControlTemplate>
</Button.Template>
</Button>
</DataTemplate>
So, it's an ItemsControl, which contains an ItemsControl, which contains buttons. This essentially creates a 2D array of buttons.
What I want to do is add an event handler to the Click event of the buttons.
Here's the catch: the code that sits behind this is written in F#. I can't, to the best of my knowledge, specify my event handler in the XAML, as F# doesn't talk to WPF in any nice way. So I need to add my event handler(s) manually in code.
Is there an easy way of doing this?
Currently, I have some F# which looks like:
let myView : ItemsControl = this?MyView
do myView.ItemsSource <- viewModel.BoardData
Here, the BoardData is a list of lists.
I was wondering if it's possible to loop through the controls in the ItemsControl, to add my event handlers? I'm having a bit of trouble doing this though. For example, in the following:
let container = myView.ItemContainerGenerator.ContainerFromItem(myView.Items.[0])
...sets container to null. In fact, all the methods I've tried from myView.ItemContainerGenerator returns null.
So, how should I go about attaching my event handler, so that I can respond to the buttons being clicked?
I have not done any Windows 7 Phone development, but I have done plenty of XAML + Silverlight development with C# and now I'm getting into doing some F# development. The approach I would take is by not using event handler's at all. Since you are using a button, make a class that derives from ICommand and add that type as a public property on your ViewModel so you could bind it to the Command property of the button. The benefits of using the ICommand interface over event handlers is that you could also have a condition on when the button is enabled to do the action.
Also, take notice that when you are doing binding expressions within (i.e. ItemTemplate) items in an ItemsControl control, the scope of what properties you can bind to are reduced to the properties of the current item. So all of the properties of the ViewModel are out of scope, unless you specify it fully i.e. <Button Command={Binding Source=ViewModel, Path=Property1.Property2.etc} />. Let me know if this helped.