Cannot resolve symbol T

Question

I have a problem with ObservableCollection Class. I cant resolve this.

using System.Collections.ObjectModel;

    #region ViewModelProperty: CustomerList
    private ObservableCollection<T> _customerList = new ObservableCollection<T>();
    public ObservableCollection<T> CustomerList
    {
      get
      {
        return _customerList;
      }

      set
      {
        _customerList = value;
        OnPropertyChanged("CustomerList");
      }
    }
    #endregion

My class with the ObservableCollection inherits ViewModelBase:

  public abstract class ViewModelBase : INotifyPropertyChanged
  {
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
      PropertyChangedEventHandler handler = PropertyChanged;

      if (handler != null)
      {
        handler(this, new PropertyChangedEventArgs(propertyName));
      }
    }
  }

any idea, where is the problem?

Answer 1

T is just a placeholder. You need to supply an actual type somewhere for T.

E.g. if you have List<T>, you could make a List<int> or List<string> (T is any other type which fits the given constraints). I.e. T is int in the first case and string in the second.

Answer 2

As previously posted, T is a placeholder. You probably want something like:

private ObservableCollection<T> _customerList = new ObservableCollection < ClassYouWantObserved > ();

Answer 3

I think that it will become clear to you when you read up a bit on Generics

You could do it like this:

ObservableCollection<Customer> customerList = new ObservableCollection<Customer>()

Then, you have a typed collection which will be able to store instances of the Customer class (and also instances of subclasses that inherit from Customer). So, if you want to have a collection where you want to be able to add instances of multiple types, you could create a base-class (or interface), and inherit from that base-class or implement this interface, and create an ObservableCollection instance for ex.