C# WPF Datagrid doesn't dynamically sort on data update

Question

I'm having some trouble with my datagrid :

When I update some data (from the model) it shows on my DataGrid, but if click on a header to sort the column it begins to go sideways when I update existing data.

Here's 2 1 example s :

• If I add a new value, it doesn't appear at the end (like it does when I don't sort the datagrid) but it shows at the wrong place (same place every time).
• If I update an existing value, the order never changes when it needs to do so.

I've seen multiple answers but some say DataGridTextColumn shouldn't be a problem... So I was wondering if it was because of the dictionary... I know that the first problem with new data had something to do with the dictionary.

Object.

    public class Player : INotifyPropertyChanged
{
    private string _id;
    private string _name;
    private int _damage;
    private int _heal;
    private int _dps;
    private int _hps;
    private int _time = 1;               

    public Player(string id, string name)
    {
        _name = name;
        _id = id;
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public string Id 
    {
        get { return _id; }
        private set
        {
            _id = value;
        }
    }

    public string Name
    {
        get { return _name; }
        private set
        {                
            _name = value;                
            NotifyPropertyChanged("Name");                
        }
    }

    public int Damage
    {
        get { return _damage; }
        set
        {
            _damage = value;                
            NotifyPropertyChanged("Damage");
            Dps = _damage / _time;
        }
    }

    public int Heal
    {
        get { return _heal; }
        set
        {
            _heal = value;
            NotifyPropertyChanged("Heal");
            Hps = _heal / _time;
        }
    }

    public int Dps
    {
        get { return _dps; }
        private set
        {
            _dps = value;
            NotifyPropertyChanged("Dps");
        }
    }

    public int Hps
    {
        get {return _hps; }
        private set
        {
            _hps = value;
            NotifyPropertyChanged("Hps");
        }
    }

    public int Time
    {
        get { return _time; }
        set
        {
            _time = value;
            Dps = _damage / _time;
            Hps = _heal / _time;
        }
    }

    private void NotifyPropertyChanged(string name)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(name));
    }

}

ObservableCollection

public sealed class ShortList
{
    private static readonly ShortList instance =  new ShortList();
    private ObservableCollection<Player> playerList = new ObservableCollection<Player>();

    private ShortList()
    {
    }

    public static ShortList getShortList
    {
        get
        {
            return instance;
        }
    }

    public ObservableCollection<Player> getPlayerList
    {
        get
        {
            return playerList;
        }
    }

    public void updatePlayer(string id, string name, int damage, int heal, int time) 
    {
        Player player;
        player = findPlayer(id);
        if (player != null)
        {                
            player.Damage = player.Damage + damage;
            player.Heal = player.Heal + heal;
            player.Time = player.Time + time;                
        }
        else
        {                
            player = new Player(id, name);
            player.Damage = damage;
            player.Heal = heal;
            player.Time = time;
            playerList.Add(player);
        }                       
    }

    public void clear()
    {
        playerList.Clear();
    }

    private Player findPlayer(string id)
    {
        foreach (Player p in playerList)
        {
            if (p.Id == id)
            {
                return p;
            }
        }
        return null;
    }

}

XAML

<DataGrid AutoGenerateColumns="False"Name="playerDataGrid" IsReadOnly="True" ItemsSource="{Binding}">
    <DataGrid.Columns>
       <DataGridTextColumn Header="Nom" Binding="{Binding Name}" MinWidth="35"/>
       <DataGridTextColumn Header="Degats" Binding="{Binding Damage}" MinWidth="45" />
       <DataGridTextColumn Header="DPS" Binding="{Binding Dps}" MinWidth="29" />
       <DataGridTextColumn Header="Soins" Binding="{Binding Heal}" MinWidth="35" />
       <DataGridTextColumn Header="HPS" Binding="{Binding Hps}" MinWidth="29" />
   </DataGrid.Columns>
</DataGrid>

Code behind the window

public partial class MiniParser : Window
{
        public MiniParser()
        {            
            InitializeComponent();
            playerDataGrid.ItemsSource = ShortList.getShortList.getPlayerList;
            temporyFill();
        }

        private void temporyFill()
        {
            ShortList.getShortList.updatePlayer("1234", "ABCD", 100, 0, 2);
            ShortList.getShortList.updatePlayer("1234", "ABCD", 100, 0, 0);
            ShortList.getShortList.updatePlayer("123", "ABC", 50, 0, 1);
            ShortList.getShortList.updatePlayer("234", "ABC", 0, 50, 1);
            ShortList.getShortList.updatePlayer("345", "BCD", 1000, 25, 25);
            ShortList.getShortList.updatePlayer("456", "CDE", 250, 0, 25);
        }

        private void startMI_Click(object sender, RoutedEventArgs e)
        {
            ShortList.getShortList.updatePlayer("5678", "BABA", 100, 100, 100);
            ShortList.getShortList.updatePlayer("1234", "ABCD", 100, 0, 0);            
        }
}

Of course most of the code behind is there for testing purpose... But the idea is that the model is being updated and the view needs to reflect the changes (Even the sorting).

Answer 1

You're not raising the PropertyChanged event when a property updates. This means that a new item which has name changed from "" to "Test" , or an existing item that changes, is not going to raise a PropertyChanged event to let the UI know a value has changed and it needs to update.

To fix it, make your properties raise the PropertyChanged event when they change.

public class Player : INotifyPropertyChanged
{
    private string _name;
    public string Name 
    {
        get { return _name; }
        set
        {
            if (_name != value)
            {
                _name = value;
                RaisePropertyChanged("Name");
            }
        }
    }

Also, I was re-reading your question and I have no idea what you're doing with ObservableDictionary , but I'd recommend changing that so your DataGrid binds directly to an ObservableCollection<Player> . I suspect that's part of your problem.

var playerCollection = new ObservableCollection<Player>();
playerCollection.Add(new Player { Name = "Test 1" });
playerCollection.Add(new Player { Name = "Test 2" });
playerCollection.Add(new Player { Name = "Test 3" });

playerDataGrid.ItemsSource = playerCollection;

Answer 2

I found a solution, so far so good :

The problem was that ObservableCollection doesn't trigger the event "CollectionChanged" when you change the value of a field in an object which is already in your ObservableCollection. (Possibly because you don't change the reference to it).

Here's an example :

ObservableCollection<MyObject> myCollection = new ObservableCollection<MyObject>();
myCollection.add("CollectionChanged","Yes");
//Let's say I had a method to find a object with the first string and to change the second string
myCollection.change("CollectionChanged", "No");

As you can guess, the second part when I changed a field of my existing object the CollectionChanged didn't trigger...

So the solution I implemented is the following :

class ObsCollection<T> : ObservableCollection<T>
    {
        public void UpdateCollection()
        {
            OnCollectionChanged(new NotifyCollectionChangedEventArgs(
                            NotifyCollectionChangedAction.Reset));
        }
    }

All you have to do is create the new type of collection and then when you change a field value of an existing object, call the UpdateCollection() method.

This solution is from Wu Xuesong.

I'd like to say Rachel as been also a big help.

Answer 3

Move any code that looks like this:

this.NotifyPropertyChanged("somepropertyname");

into the setter methods of your properties. That's what the setters are there for.

Also I second the answer suggestig you use an ObservableCollection<T> instead of your ObservableDictionary<TKey,TValue> . They are very common for WPF bindings.