The `FeedView` control

The FeedView control is one of the main ways to consume Feeds and States within an application. The FeedView uses different visual states to control what is displayed on the screen depending on the state of the underlying feed, or state.

How to use the `FeedView` control

To use the FeedView you have to add the Uno.Extensions.Reactive.UI namespace to your XAML file as follows:

<Page 
    x:Class="MyMvuxApp.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mvux="using:Uno.Extensions.Reactive.UI">

Common properties

Here are some of the notable properties of the FeedView:

Source

The Source property is the entry point of the FeedView and it's to be set with a IFeed or IState object (or their list variant).

Example:

public partial record MainModel {
    public IFeed<Person> CurrentContact => ...
}

Then in the XAML:

<Page
    ...
    xmlns:mvux="using:Uno.Extensions.Reactive.UI">

    <mvux:FeedView Source="{Binding CurrentContact}">
        <DataTemplate>
            <TextBlock Text="{Binding Data.Name}"/>
        </DataTemplate>
    </mvux:FeedView>
</Page>

The Source property of the FeedView is data bound to the CurrentContact property on the bindable proxy (which will correlate to the IFeed property with the same name on the Model).

In the above example, Data is a property of the FeedViewState instance that the FeedView creates from the IFeed and sets as the DataContext for the various templates.

State

The State property returns a FeedViewState which exposes the current state of the FeedView's underlying data Feed. It's unlikely that you'll need to access the State property directly since the FeedViewState is automatically set as the DataContext of the various templates.

The `FeedViewState` object

The FeedViewState exposes the current state of the FeedView and its underlying data Feed.

This is also the object that is passed on to the FeedView's templates for binding. So make sure you familiarize yourself with its properties detailed here.

`FeedViewState`'s Properties

Data

The Data property provides access to the value reported by the last message received from the source Feed, in other words, the current Feed value.

<Page
    ...
    xmlns:mvux="using:Uno.Extensions.Reactive.UI">

    <mvux:FeedView Source="{Binding CurrentContact}">
        <DataTemplate>
            <TextBlock Text="{Binding Data.Name}"/>
        </DataTemplate>
    </mvux:FeedView>
</Page>

In the Text property binding Data.Name of the above example, Data is a property of the FeedViewState accessible in the template, which gets the most recent Contact from the server, and then we're binding to that Contact's Name property.

Refresh

This provides a refresh command accessible from within the template which triggers the Feed to refresh itself by reloading the data from the service.

For example:

<Page
    ...
    xmlns:mvux="using:Uno.Extensions.Reactive.UI">

    <mvux:FeedView Source="{Binding CurrentContact}">
        <DataTemplate>
            <StackPanel>
                <TextBlock Text="{Binding Data.Name}" />
                <Button Content="Refresh contact" Command="{Binding Refresh}" />
            </StackPanel>
        </DataTemplate
    </mvux:FeedView>
</Page>

The Button's Command property binds to the FeedViewState's Refresh property which exposes a special asynchronous command that when called, triggers a refresh of the parent feed (in our example CurrentContact, and the data is re-obtained from the server.

Progress

This is a boolean property indicating whether the FeedView is currently under progress requesting or refreshing data from the service, and that the current data is 'transient', meaning it's to be replaced shortly with new data once available.

Error

This property returns an Exception if any occurred during the Feed's interaction with the service.

Parent

The Parent property gets the DataContext of the FeedView itself. It provides a bypass to the FeedViewState

RefreshingState

By default, the FeedView will display a progress ring while awaiting data on load or refresh:

A running progress-ring control

However, in some scenarios, you need to disable the default visual state and progress template.

This property accepts a value of the FeedViewRefreshState enumeration, which supports one of the values below which you can set to change its behavior.

None
Default / Loading

Customizing the FeedView's templates

ValueTemplate (default Template)

The ValueTemplate defines how the FeedView would be rendered when its state has concrete data to display, as opposed to no data while loading.
As mentioned previously, the FeedView provides the FeedViewState as the data item for its ValueTemplate.

The FeedView's default content directs to this property, so anything directly added to the FeedView element's XAML, is like setting its ValueTemplate.

<FeedView ...>
    <DataTemplate ... />
</FeedView>

is the same as:

<FeedView ...>
    <FeedView.ValueTemplate>
        <DataTemplate ... />
    </FeedView.ValueTemplate>
</FeedView>

or even:

<FeedView Source="..." ValueTemplate="{StaticResource MyFeedViewTemplate}" />

ProgressTemplate

This template will display when the underlying Feed is currently awaiting the asynchronous request to finish.

Its default implementation will show a progress ring:

A running progress-ring control

But you can customize that by overriding the ProgressTemplate:

<FeedView ...>
    <DataTemplate>
        ...
    </DataTemplate>

    <ProgressTemplate>
        <TextBlock Text="Please wait while requesting data..." />
    </ProgressTemplate>
</FeedView>

NoneTemplate

If you set a template to this property, it will show if the data that was returned from the service contained no entries.
For instance, if an IFeed<T> completed its request successfully with the server returning a null result, it is not considered an Error, it's considered a successful result with no data.
Similarly, when using IListFeed<T>, the NoneTemplate will also display if the collection is empty, as well as if the result is null.

Example:

<FeedView ...>
    <DataTemplate>
        ...
    </DataTemplate>

    <NoneTemplate>
        <TextBlock Text="No results were found based on your search criteria" />
    </NoneTemplate>
</FeedView>

ErrorTemplate

The FeedView will display this template if an Exception was thrown by the underlying asynchronous operation.

UndefinedTemplate

This template is displayed when the control loads, before the underlying asynchronous operation has even been called.
As soon as the asynchronous operation is invoked and awaited, the FeedView will switch to its ProgressTemplate, until the operation has resulted in data, which it will then switch to the ValueTemplate, or NoneTemplate, depending on the data result.

Typically this template will only show for a very short period - a split second or so, depending on how long it takes for the page and its Model to load.

Other notable features

Refresh command property

The FeedView provides an asynchronous Command you can bind to, which when executed, will refresh the underlying Feed by re-requesting its data source.

Here's how to utilize it:

<FeedView
    x:Name="feedView"
    ...>
    <DataTemplate>
        ...
    </DataTemplate>
</FeedView>

<Button Content="Refresh" Command="{Binding Refresh, ElementName=feedView}" />

The FeedView control

How to use the FeedView control