How to set the selectedIndex to -1 when I click a button?

Question

I would like to see the SelectedIndex property of the dataGrid when I click a button of the same view. I am trying this code:

<DataGrid.Style>
    <Style TargetType="DataGrid">
        <Style.Triggers>
            <DataTrigger Binding="{Binding ElementName=myButton, Path=IsPressed}" Value="True">
                <Setter Property="SelectedIndex" Value="-1"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</DataGrid.Style>

Butn I click the button the selectedIndex is not update. I think that the dataTrigger, how is set in the style, it is not fired, but really I am not sure.

How can I set the selectedIndex property when I click my button?

Thanks.

Answer 1

Here is the code harness code I used to see that your code works fine. I put comments around your xaml so you can match it up with your own code. The code is just a window with a basic DataGrid, Button and TextBlock bound to the SelectedIndex of your DataGrid. You can see that when you press the button the text of the TextBlock will be set -1, which is what you are setting as the value of your SelectedIndex in your DataTrigger.

Xaml:

<Window x:Class="WpfApplication1.MainWindow"
    xmlns:local="clr-namespace:WpfApplication1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <local:IntToStringConverter x:Key="intoStringConverter"/>
    </Window.Resources>
    <StackPanel>
       <DataGrid Name="dgUsers">
       <!-- Copy and paste of your code -->
           <DataGrid.Style>
               <Style TargetType="DataGrid">
                   <Style.Triggers>
                        <DataTrigger Binding="{Binding ElementName=myButton, Path=IsPressed}" Value="True">
                            <Setter Property="SelectedIndex" Value="-1"/>
                        </DataTrigger>
                   </Style.Triggers>
               </Style>
            </DataGrid.Style>
        <!---End of copy paste-->
        </DataGrid>
        <Button Name="myButton">Reset Index</Button>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="SelectedIndex: "/>
            <TextBlock Text="{Binding ElementName=dgUsers, Path=SelectedIndex, Converter={StaticResource intoStringConverter}}"/>
        </StackPanel>
    </StackPanel>
</Window>

Code behind:

using System;
using System.Windows;
using System.Windows.Data;
using System.Globalization;
using System.Collections.Generic;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            List<Test> testList = new List<Test>();
            testList.Add(new Test() { ID = 1, Name = "first" });
            testList.Add(new Test() { ID = 2, Name = "second" });
            testList.Add(new Test() { ID = 3, Name = "third" });

            dgUsers.ItemsSource = testList;
        }
    }

    public class Test
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }

    [ValueConversion(typeof(int), typeof(string))]
    public class IntToStringConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value == null)
                return "NULL";
            return value.ToString();
        }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

In my comment where I said that Button inherits IsPressed from ButtonBase. I meant that you can access the IsPressed property through an instance of a button since a Button is a subclass of ButtonBase which implements IsPressed.