Silverlight 3 - How to "refresh" a DataGrid content?

Question

I have the following scenery:

1    using System;
2    using System.Windows;
3    using System.Windows.Controls;
4    using System.Windows.Documents;
5    using System.Windows.Ink;
6    using System.Windows.Input;
7    using System.Windows.Media;
8    using System.Windows.Media.Animation;
9    using System.Windows.Shapes;
10   using System.Collections.Generic;
11   
12   namespace refresh
13   {
14      public partial class MainPage : UserControl
15      {
16          
17          List c = new List();
18   
19          public MainPage()
20          {
21              // Required to initialize variables
22              InitializeComponent();
23              c.Add(new Customer{ _nome = "Josimari", _idade = "29"});
24              c.Add(new Customer{_nome = "Wesley", _idade = "26"});
25              c.Add(new Customer{_nome = "Renato",_idade = "31"});    
26              
27              this.dtGrid.ItemsSource = c;
28          }
29   
30          private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
31          {
32              c.Add(new Customer{_nome = "Maiara",_idade = "18"});
33          }
34          
35      }
36      
37      public class Customer
38      {
39          public string _nome{get; set;}
40          public string _idade{get; set;}
41      }
42   }

Where, dtGrid is my DataGrid control...

The Question is: How to get the UI Updated after adding one more register to my list.

I get to solve it setting the DataGrid's Item Source to "" and then setting to the list of Customer objects again, like that:

1    private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
2    
3    {
4    
5    c.Add(new Customer{_nome = "Maiara",_idade = "18"});
6    
7    this.dtGrid.ItemsSource="";
8    
9    this.dtGrid.ItemsSource=c;
10   
11   }
12   

Is there a way to get the UI updated or the datagrid's itemsSource refreshed automatically after updating, altering or deleting an item from the list c ?

Thank you,

Josimari Martarelli

Solution

I recommend looking into binding, INotifyPropertyChanged, DataContexts and ObservableCollection.

1. Change your List into an ObservableCollection. That alone will probably solve some of your problems... as an ObservableCollection is a little more robust than a simple List

2. But, if you want to solve more problems like this, you will look into binding your DataGrid to your list of objects through Xaml <DataGrid... ItemsSource="{Binding MyList}">

3. In order to bind your DataGrid to your List, you will need to set the DataContext of the View. This can be a simple as placing in your constructor: this.DataContext = this; Setting your DataContext tells the view where to look for data when it sees Binding statements

4. Then, to solve problems like the one you have (changing something doesn't refresh the view), you will implement the INotifyPropertyChanged interface on your class. This will allow the code behind to send notifications to the view to tell it when something changes.

Here's the C# code that would implement this:

public partial class MainPage : UserControl, INotifyPropertyChanged
{
    private ObservableCollection<Customer> _MyList = 
        new ObservableCollection<Customer>();
    public ObservableCollection<Customer> MyList
    {
        get { return _MyList; }  
    } 

    public MainPage()
    {                      
        InitializeComponent();

        this.DataContext = this;

        MyList.Add(new Customer{ _nome = "Josimari", _idade = "29"});
        MyList.Add(new Customer{_nome = "Wesley", _idade = "26"});
        MyList.Add(new Customer{_nome = "Renato",_idade = "31"});

        OnPropertyChanged("MyList"); // This only works if you use bindings.
    }

    private void Button_Click(object sender, System.Windows.RoutedEventArgs e)
    {
        MyList.Add(new Customer{_nome = "Maiara",_idade = "18"});   

        OnPropertyChanged("MyList"); // This only works if you use bindings.
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged( string propertyName )
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    } 
}

Comments

[Learning Xamarin]

Jeremiah, Even using the 3º Version of Silverlight, is it still necessary using the ObservableCollection to notify property changes? Thank You, Josimari Martarelli

[Jeremiah]

According to the MSDN site ( msdn.microsoft.com/en-us/library/ms668604(VS.95).aspx ) The observable collection should notify when Items are Added or Removed... But it won't notify when items are Updated. Because of this, I always recommend the pattern of Notifying whenever the list changes. It's a good habit. Good luck!