C# – asp.net gridview command field and custom edit

Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class.

public class MyClass
{
    // this is a field.  It is private to your class and stores the actual data.
    private string _myField;

    // this is a property. When accessed it uses the underlying field,
    // but only exposes the contract, which will not be affected by the underlying field
    public string MyProperty
    {
        get
        {
            return _myField;
        }
        set
        {
            _myField = value;
        }
    }

    // This is an AutoProperty (C# 3.0 and higher) - which is a shorthand syntax
    // used to generate a private field for you
    public int AnotherProperty { get; set; } 
}

@Kent points out that Properties are not required to encapsulate fields, they could do a calculation on other fields, or serve other purposes.

@GSS points out that you can also do other logic, such as validation, when a property is accessed, another useful feature.

It's a little trickier when you want to put it into edit mode based on data. You tell the datagrid which of it's displayed rows is editable, not which data you want to be editable, so you'll need to go through each of the rows in the grid, see if it matches the id, and set the EditItemIndex to the appropriate value and rebind.

You could look at the source data and get the row number from that before you bind, but then you may have problems with paging, sorting etc.

It's a bit messy having to rebind the grid, but I can't think of a better way off the top of my head.

public partial class _Default : System.Web.UI.Page
{

    private DataTable GetData()
    {
        DataTable tTable = new DataTable();
        tTable.Columns.Add(new DataColumn("Column1", typeof(int)));
        tTable.Columns.Add(new DataColumn("Column2", typeof(string)));

        DataRow tRow = tTable.NewRow();
        tRow["Column1"] = 1;
        tRow["Column2"] = "Test1";
        tTable.Rows.Add(tRow);

        tRow = tTable.NewRow();
        tRow["Column1"] = 2;
        tRow["Column2"] = "Test2";
        tTable.Rows.Add(tRow);

        tRow = tTable.NewRow();
        tRow["Column1"] = 3;
        tRow["Column2"] = "Test3";
        tTable.Rows.Add(tRow);

        tRow = tTable.NewRow();
        tRow["Column1"] = 4;
        tRow["Column2"] = "Test4";
        tTable.Rows.Add(tRow);

        tRow = tTable.NewRow();
        tRow["Column1"] = 5;
        tRow["Column2"] = "Test5";
        tTable.Rows.Add(tRow);

        return tTable;
    }

    private void BindData()
    {
        DataTable tTable = GetData();

        TestGrid.DataSource = tTable;
        TestGrid.DataBind();

        if (!String.IsNullOrEmpty(Request.QueryString["edit"]))
        {
            foreach (DataGridItem tRow in TestGrid.Items)
            {
                if (tRow.Cells[0].Text == Request.QueryString["edit"])
                    TestGrid.EditItemIndex = tRow.ItemIndex;
            }
            TestGrid.DataBind();
        }
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
            BindData();
    }
}

You should be able to fire that up (with a datagrid added to the ASPX obviously) then put ?edit= on the end of the URL to get it to open the relevent entry in edit mode.