Programmatically select and highlight datagriditem MVVM

Question

I have trouble when I try to select some Item in DataGrid programmatically. Without using MVVM pattern all is OK. Look at XAML:

    <DataGrid 
        Name="_dataGrid"
        AutoGenerateColumns="False"
        SelectedItem="{Binding SelectedItem, Mode=TwoWay}">
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding Name}"/>
            <DataGridTextColumn Binding="{Binding SecondName}"/>
        </DataGrid.Columns>
    </DataGrid>

Code behind:

    public class GridItem
    {
        public String Name { get; set; }
        public String SecondName { get; set; }
    }

    public partial class Window1 : Window
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void RaisePropertyChanged(String propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        private GridItem _selectedItem;
        public GridItem SelectedItem
        {
            get { return _selectedItem; }
            set
            {
                _selectedItem = value;
                RaisePropertyChanged("SelectedItem");
            }
        }

        public Window1()
        {
            InitializeComponent();
            DataContext = this;

            _dataGrid.Loaded += DataGridLoaded;
            Init1();
        }

        void DataGridLoaded(object sender, RoutedEventArgs e)
        {
            Int32 rowIndex = 2;
            var selItem = _dataGrid.Items[rowIndex];

            SelectedItem = (GridItem)selItem;     <-------- Bad
            //_dataGrid.SelectedItem = selItem;   <-------- Good
        }

        private void Init1()
        {
            var source = new List<GridItem>();
            source.Add(new GridItem
            {
                Name = "pavlik",
                SecondName = "bobr"
            });
            source.Add(new GridItem
            {
                Name = "alex",
                SecondName = "ugr"
            });
            source.Add(new GridItem
            {
                Name = "den",
                SecondName = "ivanov"
            });
            source.Add(new GridItem
            {
                Name = "dima",
                SecondName = "klim"
            });
            _dataGrid.ItemsSource = source;
        }
    }

So, when I select Item like that

_dataGrid.SelectedItem = selItem; // Good

Item is selected and highlighted properly.

But when I try to select and highlight Item via Model property, Item is not highlighted!

SelectedItem = (GridItem)selItem; // Bad

What is the reason? Any idea?

Answer 1

you need to inherit your window or any viewmodel class from INotifyPropertyChanged otherwise it will not Notifies clients that a property value has changed.

for your case it could be like

public partial class Window1 : INotifyPropertyChanged
{
    // Class code goes here;
    public event PropertyChangedEventHandler PropertyChanged;
    protected void RaisePropertyChanged(String propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

Answer 2

I do this a lot, DataGrid to ViewModel, and I never have to do

SelectedItem = (GridItem)selItem;

i.e cast the item.

As you have SelectedItem on the DataGrid XAML, it knows the type you are binding too.

However, I normally use ItemSource on the gridview as well.

e.g. ItemSource = "{Bind the collection of GridItem}"

so in ViewModel, I would have Observablecollection or List as a property.

My WPF knowledge is only like 2 weeks old so I could be totally be wrong, but I think the cast and the Itemsource is where you need to look.

I could give you an example if you like.

Cheers