Question

When you update DataGridView.DataSource using the assignment operator, the DataSourceChanged event handler is called. You can’t overload assignment op in C#, so how does the event handler get called internally?

public void foo(){
    this.dataGridView.DataSourceChanged += new EventHandler(bar);
    this.dataGridView.DataSource = dt;
}

//this handler is called after datasource changes
private void bar(object sender, EventArgs e) {}

Answer 1

DataSource is implemented as a property.

private object _dataSource;
public object DataSource {
    get
    {
        return _dataSource;
    }
    set
    {
        if (value != _dataSource) {
            _dataSource = value;
            UpdateTheDataGridView();
            RaiseTheDataSourceChangedEvent();
        }
    }
}

A read/write property is a set of two methods, which are automatically called, when you access the property; set when you assign a value, get when you read the property.

Note also, that a change is only registered if you assign a data source something different. This means that you cannot refresh the grid by re-assigning the same data source.

var list = new List<string> { "a", "b", "c" };
dgv.DataSource = list;

list.Add("d");
dgv.DataSource = list; // Does not work.

Workaround:

list.Add("d");
dgv.DataSource = null; // <== this does the trick.
dgv.DataSource = list;