Question

In my .aspx page, I have an <asp:GridView runat="server" ID="CustomerGridView"> control which I bind like this:

public partial class InsertCustomer : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ViewCustomer();
        }
    }

    private void ViewCustomer()
    {
        var manager = new DomainManager();
        var result = manager.FindAll(new Customer());
        this.CustomerGridView.DataSource = result;
        this.CustomerGridView.DataBind();
    }
}

Here is the DomainManager class:

public class DomainManager
{
    readonly StringBuilder _queryBuilder = new StringBuilder();
    private Type _entityType;
    readonly SQLHelper _sqlHelper = new SQLHelper();

    public IEnumerable FindAll<T>(T entity)
    {
        _entityType = entity.GetType();
        var query = string.Format("select * from {0}", _entityType.Name);
        var dt = _sqlHelper.FillDataTable(query);
        return dt.AsEnumerable();
    }
}

The problem is that my grid is not being bound correctly. Why not?

Answer 1

Try changing

return dt.AsEnumerable(); 

to

return dt.DefaultView;

Explanation: By default, a GridView binds to actual properties of an object. For example, if the data source is a List<Customer>, then you can bind to the Name property of each Customer. But when the data source is a DataTable of customers, then each customer is represented by a DataRow, and a DataRow does not have a Name property that the GridView can bind to.

To support dynamic properties, an object must implement the ICustomTypeDescriptor interface. This interface is implemented by DataRowView but not DataRow. By changing the code to return dt.DefaultView (which is a DataView), you provide the GridView with a collection of DataRowView objects that it can bind to.

Now you might be wondering why

this.CustomerGridView.DataSource = dt;

works, but

this.CustomerGridView.DataSource = dt.AsEnumerable();

doesn’t.

The reason is that DataTable implements the IListSource interface, which tells the GridView “don’t use me as the data source, use my DefaultView instead.” But AsEnumerable() returns a wrapper object that doesn’t implement IListSource, so the GridView doesn’t know how to get to the DefaultView.