How to know which Xamarin Forms Entry has been modified in a ListView?

Question

I'm working with Xamarin.Forms in a PCL project.

I have a page/screen where there are an ListView control. I have created a custom DataTemplate for ViewCell.

This ViewCell has different controls: some Labels, one Button and also a Entry.

<ListView x:Name="lvProducts" >
  <ListView.ItemTemplate>
    <DataTemplate>
      <ViewCell>
        <StackLayout BackgroundColor="#FFFFFF" Orientation="Vertical">
          <Grid Padding="5">
            ...
            <Button Grid.Row="0" Grid.Column="1" Text="X" 
                    CommandParameter="{Binding MarkReference}"
                    Clicked="DeleteItemClicked" />
            ...
            <StackLayout Grid.Row="2" Grid.ColumnSpan="2" Orientation="Horizontal" >
              <Label Text="Ref.: " FontSize="24" FontAttributes="Bold" TextColor="#000000" />
              <Label Text="{Binding Reference}" FontSize="24" TextColor="#000000" />
            </StackLayout>
            ...
            <Entry Grid.Row="3" Grid.Column="1" Text="{Binding NumElements}"
                   Keyboard="Numeric" Placeholder="" FontSize="24"
                   HorizontalTextAlignment="Center"  Focused="OnItemFocus"    
                   Unfocused="OnItemUnfocus" />
         </Grid>
       </StackLayout>   
      </ViewCell>
    </DataTemplate>
  </ListView.ItemTemplate>
</ListView>

I want to achieve two things with this Entry control that I'm not able achieve:

First, when I add a new item, I would like that this new item has his Entry the focus, ready to start typing.

Second, when the user ends to write a value into the Entry, I would like to change the value of the behind. I would like know which Entry of ListView has modified. I tried to use the Unfocused event, but in the params of the method that launches only has a sender param that returns the Entry object, no reference about the model that has binded.

    public void OnItemUnfocus(object sender, EventArgs e)
    {
        Entry entry = (Entry)sender;
        //Here I would like to know the model object that's binded 
        //with this Entry / CellView item
    }

How I can achieve these two points?

Regarding the second point, if you need to access the data object, you can override OnBindingContextChanged in the cell, and then obtain the object with var object = (YourClass)BindingContext. This way you can access the object in the data source whenever you need it. — papafe
Thank you @markusian, I got your idea, and I have used it. I extended the Entry control and I used into Unfocused event. Works fine. — stivex

Yehor Hromadskyi Yehor Hromadskyi · Accepted Answer · 2016-03-24T09:26:17

I'd like to suggest you to use behaviors:

public class FocusBehavior : Behavior<Entry>
{
    private Entry _entry;

    public static readonly BindableProperty IsFocusedProperty =
        BindableProperty.Create("IsFocused",
                                typeof(bool),
                                typeof(FocusBehavior),
                                default(bool),
                                propertyChanged: OnIsFocusedChanged);

    public int IsFocused
    {
        get { return (int)GetValue(IsFocusedProperty); }
        set { SetValue(IsFocusedProperty, value); }
    }

    protected override void OnAttachedTo(Entry bindable)
    {
        base.OnAttachedTo(bindable);

        _entry = bindable;
    }

    private static void OnIsFocusedChanged(BindableObject bindable, object oldValue, object newValue)
    {
        var behavior = bindable as FocusBehavior;
        var isFocused = (bool)newValue;

        if (isFocused)
        {
            behavior._entry.Focus();
        }
    }
}

<ListView x:Name="TasksListView"
          ItemsSource={Binding Tasks}
          RowHeight="200">
  <ListView.ItemTemplate>
    <DataTemplate>
      <ViewCell x:Name="ViewCell">
        <Grid x:Name="RootGrid"
              Padding="10,10,10,0"
              BindingContext="{Binding}">
          <Entry>
              <Entry.Behaviors>
                <helpers:FocusBehavior IsFocused="{Binding BindingContext.IsFocused, Source={x:Reference RootGrid}}"/>
              </Entry.Behaviors>
          </Entry>
        </Grid>
      </ViewCell>
    </DataTemplate>
  </ListView.ItemTemplate>
</ListView>

And my model:

public class TaskModel : INotifyPropertyChanged
{
    private bool _isFocused;

    public bool IsFocused
    {
        get { return _isFocused; }
        set
        {
            _isFocused = value;
            RaisePropertyChanged();
        }
    }

And in ViewModel, after adding new item, set it's IsFocused property to true.

The same thing with behavior you could use for TextChanged for Entry.

How to know which Xamarin Forms Entry has been modified in a ListView?

2 Answers