C# - Calling functions from a different class

Question

I have 4 classes

Comment Class:

public class comment
    {
        public string Username { get; set; }
        public string Comment { get; set; }

        public comment(string _username, string _comment)
        {
            this.Username = _username;
            this.Comment = _comment;
        } 
    }

Pin Class:

   public class Pin : PhoneApplicationPage

        public List<comment> Comment_List;        

    public Pin(){

        this.Comment_List = new List<comment>();
    }
}

Message Page:

public partial class MessagePage : PhoneApplicationPage
{
   Pin _Pin;

   public MessagePage(Pin _pin)
 {        
    this._Pin = _pin;
 }

 public void Refresh()
 {
   this.textbox1.Text = "";
   foreach (comment c in this._Pin.List)
   {
    this.textbox1.Text += c.Username;
   }

  }

public void function()
{
     //Call static function in another class to download new pin info
}

The static function then updates a static class called PinList().

I have an event triggered in PinList() class when Its static List of Pins is updated, How to i address the object that is the current MessagePage to to call a function to update the textbox with the new values in Pin.comments.

i.e. i Have:

public class PinList
    {
        public ObservableCollection<Pin> list;
        public static ObservableCollection<Pin> MainPinList = new ObservableCollection<Pin>();
        public event PropertyChangingEventHandler PropertyChanged;

public PinList()
        {
            list = new ObservableCollection<Pin>();
            list.CollectionChanged += listChanged;            

            ((INotifyPropertyChanged)list).PropertyChanged += new PropertyChangedEventHandler(list_Property_Changed);

        }


    private void list_Property_Changed(object sender, PropertyChangedEventArgs args)
            {
                  //Need to call
                  //MessagePage.Refresh();
            }

Answer 1

From the code you've got and the way you've worded it it sounds like you're trying to access MessagePage statically as if it was a singleton but there's not a single static Property anything there. If you're dead-set on doing it that way you'll need to declare a static instance of MessagePage.

I would recommend, however, that you simply bind an ItemsControl of some sort to react to the Pin.Comment_List and make Comment_List an ObservableCollection<comment> instead of a List<comment> and make sure the comment class implements INotifyPropertyChanged - then the UI will take care of its own updates. It looks like what you're doing is trying to reinvent the wheel.

Edit: Based on your comments

public class Comment : INotifyPropertyChanged
{
    private string username;
    private string comment;

    public comment(string _username, string _comment)
    {
        this.Username = _username;
        this.Comment = _comment;
    }                 

    public string Username
    {
        get
        {
            return username;
        }

        set
        {
            if(value != username)
            {
                username = value;
                NotifyPropertyChanged("Username");
            }
        }
    }                   

    public string Comment
    {
        get
        {
            return comment;
        }

        set
        {
            if(value != comment)
            {
                comment= value;
                NotifyPropertyChanged("Comment");
            }
        }
    }       

    public event PropertyChangedEventHandler PropertyChanged;

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

Pin Class:

public class Pin
{
    private readonly ObservableCollection<Comment> commentList = new ObservableCollection<Comment>();        

    public ObservableCollection<Comment> CommentList
    {
        get
        {
            return commentList;
        }
    }
}

Message Page:

public partial class MessagePage : PhoneApplicationPage
{
    private readonly Pin pin;

    public MessagePage(Pin _pin)
    {        
        this.pin = _pin;
    }

    public Pin Pin
    {
        get
        {
            return pin;
        }
    }

And your data source

public class PinList
{
    public ObservableCollection<Pin> list;
    public static ObservableCollection<Pin> MainPinList = new ObservableCollection<Pin>();

    public void Refresh()
    {
         // Here you update the comments list of each of your Pins - The comment
         //     list is an ObservableCollection so your display will automatically
         //     update itself. If you have to change an existing comment due to
         //     an edit or something that will automatically update as well since
         //     we've implemented INotifyPropertyChanged
    }
}

Displaying a Pin's comments would look something like this as long as you implemented INotifyPropertyChanged on comment and changed Comment_List to an ObservableCollection<comment>. All you would need to do in order to update the messages is add any new messages to that pin's Comments_List and the UI will react without you having to do anything in singleton or subscribe to a bunch of events.

<ItemsControl DataContext={Binding Pin} ItemsSource="{Binding CommentList}"">
  <ItemsControl.ItemTemplate>
    <DataTemplate>
      <StackPanel Margin="0 0 0 10">
        <TextBlock Text="{Binding Username, StringFormat='{0} said:'}" FontWeight="Bold" />
        <TextBlock Text="{Binding Comment}" />
      </StackPanel>
    </DataTemplate>
  </ItemsControl.ItemTemplate>
</ItemsControl>