UWP Accessing content in a data bound ListView - win-universal-app

Question

I have a ListView with a ListView.ItemTemplate if it is important: the ListView is part of a Grid). I will strip it down here for the minumum:
<ListView x:Name="lstFotos" Grid.Row="2" Grid.Column="1" Height="auto" Tapped="imageControl_Tapped" >
<ListView.ItemTemplate>
<DataTemplate>
<Grid IsTapEnabled="True" >
<Grid.RowDefinitions>
<RowDefinition Height="50" />
<RowDefinition Height="50"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Image x:Name="imageControl" Width="200" Height="200" Source="{Binding DateiSoftwareBitmapSource}" IsTapEnabled="True" Grid.Column="0" Grid.Row="0" Grid.RowSpan="2" />
<TextBlock x:Name="txtImageDateDescription" Text="Aufnahmedatum: " Grid.Column="1" Grid.Row="0" />
<TextBlock x:Name="txtImageDescriptionDescription" Text="Beschreibung: " Grid.Column="1" Grid.Row="1" />
<TextBlock x:Name="txtImageDate" Text="{Binding Datum}" Grid.Column="2" Grid.Row="0" />
<TextBox x:Name="txtImageDescription" Text="{Binding Beschreibung}" Grid.Column="2" Grid.Row="1" />
<Button x:Name="btnSpeichern" Content="Speichern" Grid.Column="3" Grid.Row="1" Click="btnSpeichern_Click" />
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
In the code behing I do a
lstFotos.ItemsSource = AlleAnzeigeFotos
AlleAnzeigeFotos is a List(Of myClass), myClass contains the properties Datum, Beschreibung, DateiSoftwareBitmapSource.
What I want to do is that the user can edit the textfield, presses on the button and in the code behing I want to update the class and do some more stuff.
How can I get the appropriate instance of that class when I click the button?
UPDATE:
This is how it looks like:
"Beschreibung" (english: description) is empy after adding a foto and should be editable and stored by clicking "Speichern" (save).

Answer 1

(sender as Button).DataContext will give you the item which you clicked. Cast it to appropriate type of your class
update
Text="{Binding Beschreibung,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
var userenteredstring=((sender as Button).DataContext as your class).Beschreibung