Binding with Prism Navigation - xaml

Question

I'm trying to bind string path in XAML using prism navigateto extension method from a button in ListView.
Apparently the BindingContext isn't recognized to be the same as in the ListView
Here's the sample code of what i'm trying to achieve.
<ListView
x:Name="MainMenu"
CachingStrategy="RetainElement"
HasUnevenRows="True"
ItemsSource="{Binding MenuItems}"
Margin="20,0,0,0"
SeparatorVisibility="Default">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<buttons:SfButton
Style="{StaticResource BaseButtonStyle}"
HeightRequest="70"
TextColor="{StaticResource MenuTextColor}"
Text="{Binding Title}"
HorizontalTextAlignment="Start"
VerticalOptions="CenterAndExpand"
HorizontalOptions="FillAndExpand"
ImageSource="{Binding MenuItemType, Converter={StaticResource MenuItemTypeConverter}}"
ShowIcon="True"
Command="{prism:NavigateTo Name={Binding Item.View}}"
/>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Any ideas how to set the binding in this situations?
Regards.

Answer 1

Within any sort of ListView, CollectionView, etc where you are binding an ItemsSource and then have some sort of DataTemplate to display an individual item in that collection, the Binding Context within that DataTemplate is the individual item in the collection not the ViewModel that that provides the Binding Context of both your Page and the ListView.
There are technically a couple parts to this that you will want to understand. Let's say that your model looks like:
public class FooModel
{
public string Text { get; set; }
public string NavigationPath { get; set; }
}
And let's say that you have a collection of FooModel like:
public ObservableCollection<FooModel> FooItems { get; }
In XAML you might have something like:
<ListView ItemsSource="{Binding FooItems}">
However when you go to reference properties of FooItem you will just reference them like:
<ListView.DataTemplate>
<DataTemplate>
<ViewCell>
<Button Text="{Binding Text}"
Command="{prism:NavigateTo Name={Binding NavigationPath}" />
</ViewCell>
</DataTemplate>
</ListView.DataTemplate>
Now assuming that the issue isn't that you're just adding Item erroneously, let's look at some other possible issues/solutions. To start let's look at the start of our page.
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:prism="http://prismlibrary.com"
x:Name="page"
x:Class="HelloWorld.Views.ViewA">
The big thing to notice here is that I've added the x:Name attribute so that I can reference the page itself later. In general within the context of something like a ListView if I need to access say the FooCommand property within my ViewModel I might would change my XAML markup from:
<Button Command="{Binding FooCommand}" />
To instead look at the Page's BindingContext like this:
<Button Command="{Binding BindingContext.FooCommand, Source={x:Reference page}}" />
While this will help you in general within your ListView it still doesn't necessarily help you with the issue of using Prism's Navigation Extensions. For this you may need to pass in the SourcePage like the following:
<Button Command="{prism:NavigateTo 'Foo', SourcePage={x:Reference page}}" />
In the event this doesn't work for some reason then you may be possible that the BindingContext isn't getting set properly on the Navigation Extension itself. To work around this you would want to update your command as follows:
<Button x:Name="cellButton"
Command="{prism:NavigateTo Name={Binding View},
BindingContext={x:Reference cellButton}}" />
Note that if you need to reference the SourcePage or add the BindingContext to resolve your issue, please provide a sample that reproduces the issue and open an issue on GitHub.