c# - How to set Binding Context of ListView button to the binding context of parent in Xamarin Forms

Question

Basically, I have a ListView with a DataTemplate Selector that uses a particular DataTemplate basing on the ListView item.

Now, in the DataTemplate - I have a button w/ a command that should be binded on the ViewModel of the Parent (or the ListView) itself.

Note that I only want to bind the Command property of the button as the Text and other properties would need to be binded to the current binding Context of the button.

The BindingContext of the DataTemplate is the ListView Item bindingContext (Message Model in this case) but I want to be able to bind just a specific button in the data template to the viewmodel of the parent listView.

How do I do that?

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage 
        xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
        x:Class="MobileMobile.Views.MobileMessageListView"
        Title="Message List"
        NavigationPage.BarBackgroundColor="#FF9100"
        NavigationPage.BarTextColor="White"
        xmlns:ViewSwitchers="clr-namespace:MobileMobile.ViewSwitchers;assembly=MobileMobile"
        xmlns:ViewCells="clr-namespace:MobileMobile.ViewCells;assembly=MobileMobile"
        xmlns:Extensions="clr-namespace:MobileMobile.Extensions;assembly=MobileMobile"
        >

    <ContentPage.Resources>
        <ResourceDictionary>
            <DataTemplate x:Key="botMessageDataTemplate">
                <ViewCell>
                    <Button Text="Hello!" Command="{Binding TestCommand, Source=???}" CommandParameter="Hello"/>
                </ViewCell>
            </DataTemplate>

            <ViewSwitchers:MobileMessageTemplateSwitcher x:Key="MobileMessageTemplateSwitcher" BotMessageDataTemplate="{StaticResource botMessageDataTemplate}" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <ContentPage.Content>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="Auto" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>

            <StackLayout Grid.Row="0" Orientation="Vertical" x:Name="MainViewStack">
                <ListView
                        CachingStrategy="RecycleElement"
                        BackgroundColor="Transparent"
                        ItemTemplate="{StaticResource MobileMessageTemplateSwitcher}"
                        IsPullToRefreshEnabled="true"
                        RefreshCommand="{Binding RefreshCommand}"
                        ItemsSource="{Binding Messages}"
                        HasUnevenRows="true"
                        IsRefreshing="{Binding IsLoading, Mode=OneWay}"
                        SeparatorVisibility="None">
                    <ListView.Footer/>
                </ListView>
            </StackLayout>
            <StackLayout Grid.Row="1" Orientation="Horizontal" HeightRequest="50">
                <Entry Text="{Binding CurrentMessageText}" Placeholder="{Binding MessageTextPlaceHolder}" HorizontalOptions="FillAndExpand"/>
                <Button Text="SEND" Command="{Binding SendMessageCommand}"/>
            </StackLayout>
        </Grid>
    </ContentPage.Content>
</ContentPage>

Answer 1

Try this:

<Button
    Text="Hello!"
    Command="{Binding Path=BindingContext. TestCommand, Source={x:Reference Name=MessageListPage}}"
    CommandParameter="Hello" />

You would have to give the Page an x:Name property with the value MessageListPage, so it messes with your pure MVVM a bit, but since Xamarin XAML doesn't support relative binding (as far as I know..) this is the way to go.