How to bind a list count to a label

Question

I have a DataGridView binding to a list and a label showing number of records. I run into the same problem Khash had. (so I steal his title). Any add or delete operations on the grid won't update the label.

Based on Sung's answer, a facade wrapper, I create my custom list inheriting BindingList and implementing INotifyPropertyChanged.

public class CountList<T> : BindingList<T>, INotifyPropertyChanged
{    
    protected override void InsertItem(int index, T item)
    {
        base.InsertItem(index, item);
        OnPropertyChanged("Count");
    }

    protected override void RemoveItem(int index)
    {
        base.RemoveItem(index);
        OnPropertyChanged("Count");
    }

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

However, this will throw an exception when binding.

Cannot bind to the property or column Count on the DataSource. Parameter name: dataMember

Below is my binding code:

private CountList<Person> _list;

private void Form1_Load(object sender, EventArgs e)
{
    _list = new CountList<Person>();
    var binding = new Binding("Text", _list, "Count");
    binding.Format += (sender2, e2) => e2.Value = string.Format("{0} items", e2.Value);
    label1.DataBindings.Add(binding);
    dataGridView1.DataSource = _list;
}

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Any suggestions will be appreciated. Thank you.

Answer 1

In fact, it is much simpler than you think!

Microsoft already has created the BindingSource control, so, you need to use it and then handle the BindingSource event to update the label:

    public class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    private BindingSource source = new BindingSource();

    private void Form1_Load(object sender, EventArgs e)
    {
        var items = new List<Person>();
        items.Add(new Person() { Id = 1, Name = "Gabriel" });
        items.Add(new Person() { Id = 2, Name = "John" });
        items.Add(new Person() { Id = 3, Name = "Mike" });
        source.DataSource = items;
        gridControl.DataSource = source;
        source.ListChanged += source_ListChanged;

    }

    void source_ListChanged(object sender, ListChangedEventArgs e)
    {
        label1.Text = String.Format("{0} items", source.List.Count);
    }