C# WPF Appending DataGrid

Question

I can only ever seem to get it to add the first line but then it stops. I want to basically use it as a way to save program history. So everytime the button clicks, a new line is added. Obviously the code would add static info except the timestamp for right now.

Thanks!!

      private void test_Click(object sender, RoutedEventArgs e)
    {

        {
            InitializeComponent();

            string nowtime = DateTime.Now.ToString("MM/dd/yyyy HH:mm");

            List<User> users = new List<User>();
            users.Add(new User() { ID = "1", Query = "John Doe", Timestamp = nowtime });

            historyData.ItemsSource = users;
        }
    }

    public class User
    {
        public string ID { get; set; }
        public string Query { get; set; }
        public string Timestamp { get; set; }
    }

Answer 1

Set this outside of the button click List<User> users = new List<User>();

On your button,

private void Button_Click(object sender, RoutedEventArgs e)
{
    string nowtime = DateTime.Now.ToString("MM/dd/yyyy HH:mm:ss");

    users.Add(new User() { ID = "1", Query = "John Doe", Timestamp = nowtime });

    // To refresh datagrid source set null first then the data.
    historyData.ItemsSource = null;
    historyData.ItemsSource = users;
}

Answer 2

There are a few things wrong with the posted code:

1. You're creating a new list everytime the click event is fired, and setting this new list as the ItemsSource. This is the reason why only one row is ever in the grid

2. You're unnecessarily calling InitializeComp.nets in the click event. This belongs in the constructor.

3. Use an ObservableCollection instead of List for a grid's ItemsSource. This will remove the need for constantly assigning a new List everytime a change has occured.

The changes will look something like this:

private readonly ObservableCollection<User> users = new ObservableCollection<User>();

....

public Form1()
{
    InitializeComponets ();
    ....
    historyData.ItemsSource = users;
}

....

private void test_Click(object sender, RoutedEventArgs e)
{
    string nowtime = DateTime.Now.ToString("MM/dd/yyyy HH:mm");

    users.Add(new User() { ID = "1", Query = "John Doe", Timestamp = nowtime });
}

Answer 3

Either add the new item directly to the Items property:

private void test_Click(object sender, RoutedEventArgs e)
{
    string nowtime = DateTime.Now.ToString("MM/dd/yyyy HH:mm");
    historyData.Items.Add(new User() { ID = "1", Query = "John Doe", Timestamp = nowtime });
}

Or set the ItemsSource once and keep a reference to the source collection:

private readonly ObservableCollection<User> _users = new ObservableCollection<User>();

public MainWindow()
{
    InitializeComponent();
    historyData.ItemsSource = _users;
}

private void test_Click(object sender, RoutedEventArgs e)
{
    string nowtime = DateTime.Now.ToString("MM/dd/yyyy HH:mm");
    _users.Add(new User() { ID = "1", Query = "John Doe", Timestamp = nowtime });
}

You need to use an ObservableCollection<T> for the control to be notified when a new item is added.