Accessing an element inside of a Collectionview datatemplate in Xamarin.Forms - xamarin.forms

Question

I am fairly new to Xamarin.Forms and am attempting to access a child element of a CollectionView DataTemplate.
The DataTemplate contains a horizontal StackLayout consisting of a Checkbox and a Label.
What I would like to do is to make the Checkbox's IsChecked property equal to true whenever the CollectionView element is selected, in order to show the Checkbox as checked when an element is selected.
The highest number of elements that I will ever have in this CollectionView are 2.
Here is some code to illustrate what I am trying to do:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class="CheckBoxExample.MainPage">
<StackLayout>
<!-- Place new controls here -->
<Label
Text="Welcome to Xamarin.Forms!"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<Frame>
<CollectionView
ItemsSource="{Binding Customers}">
<CollectionView.ItemTemplate>
<DataTemplate>
<StackLayout
Orientation="Horizontal">
<CheckBox
IsChecked="" />
<Label
Text="{Binding .}"
VerticalOptions="Center" />
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</Frame>
</StackLayout>
</ContentPage>

Answer 1

In order to check a CheckBox whenever it is selected, and uncheck it when it is unselected, and assuming, as you mentioned, that you will only have two items, the following code should put you on the right track:
First, We define our model in the following way
public class Costumer : INotifyPropertyChanged
{
private String _Text;
public String Text
{
get => _Text;
set
{
if (_Text != value)
{
_Text = value;
OnPropertyChanged();
}
}
}
private Boolean _Checked;
public Boolean IsChecked
{
get => _Checked;
set
{
if (_Checked != value)
{
_Checked = value;
OnPropertyChanged();
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class Costumers : List<Costumer>, INotifyPropertyChanged
{
private Costumer _CostumerSelected;
public Costumer CostumerSelected
{
get => _CostumerSelected;
set
{
if (_CostumerSelected != value)
{
if (_CostumerSelected!=null) _CostumerSelected.IsChecked = false;
_CostumerSelected = value;
OnPropertyChanged();
_CostumerSelected.IsChecked = true;
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
In the previous code, note what is going on in the CostumerSelected setter: If the selection changed, and an item is already selected, it is unchecked. After that, the new selected item is checked.
Then in the XAML
<ContentPage.Content>
<StackLayout>
<Frame >
<CollectionView ItemsSource="{Binding .}"
SelectedItem="{Binding CostumerSelected}"
SelectionMode="Single">
<CollectionView.ItemTemplate>
<DataTemplate>
<StackLayout Orientation="Horizontal">
<CheckBox IsChecked="{Binding IsChecked}" />
<Label Text="{Binding Text}"
VerticalOptions="Center" />
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</Frame>
</StackLayout>
</ContentPage.Content>
In the code above, note that i assigned the SelectionMode property, in order to allow selection! Also, i bound the SelectedItem property to the CostumerSelected in my Costumers Model.
And in the code behind, we simply populate the CollectionView:
protected override void OnAppearing()
{
BindingContext = new Costumers() { new Costumer() { Text = "James Sku" }, new Costumer() { Text = "Daniel Gomez" } };
base.OnAppearing();
}