Last week I wrote down why I believe the model should not have anything about columns. In .NET many people only ever used DataTables as their models. Because of that they often believe that in .NET the model must contain the columns.
They forget that DataGridView ‘s DataSource doesn’t require a DataTable at all, DataTable just happens to implement what DataSource needs: IList. It’s correct that if the model has all information that .NET’s many databinding components will get all the information they need out of your model. But it ain’t true that this is the only way nor a by-design in .NET. In .NET the by-design is that the view has all this and the model *can* pass it, if it has it, but it doesn’t have to.
In this example I illustrate that in .NET you can do a databinding with a simple .NET array. In .NET simple arrays implement IList. When a column of the DataGridView isn’t ReadOnly the property setter of the instance in the array will be called after the user edited the cell. I’ll illustrate this in the dataGridView1_CellEndEdit method: the property setter of the property Age of the Person instance being edited will be called. The view will as a result of a Refresh fetch the model’s new values. The Changed property will be rendered as True, for the Person that got changed.
People with VS.NET can drag a DataGridView and a Button on a Windows Form, and copypaste the Person class, button1_Click’s and dataGridView1_CellEndEdit’s code over. It’ll work.
// No DataTable, I'm not even importing System.Data, IList is fine
using System;
using System.Windows.Forms;
public partial class Form1 : Form
{
public Form1() [+]
private void button1_Click(object sender, EventArgs e) {
dataGridView1.AutoGenerateColumns = false;
DataGridViewColumn column;
column = new DataGridViewTextBoxColumn();
column.DataPropertyName = "Name";
column.HeaderText = "The name of the person";
column.Width = 180;
// As you can see we are not doing anything on the model
// to tell the view what the columns are.
dataGridView1.Columns.Add(column);
column = new DataGridViewTextBoxColumn();
column.DataPropertyName = "Age";
column.HeaderText = "The age";
column.Width = 70;
// Let's make this one editable
column.ReadOnly = false;
// We're just telling the view about the properties it
// needs to bind, using the DataPropertyName member of
// a DataGridViewColumn
dataGridView1.Columns.Add(column);
// Let's add a column that will show us that the view
// will fetch property values at refresh
column = new DataGridViewTextBoxColumn();
column.DataPropertyName = "Changed";
column.HeaderText = "?";
column.Width = 45;
dataGridView1.Columns.Add(column);
// This is a normal array in .NET: it implements IList.
// An IList is a collection with a known order.
Person[] people = new Person[2];
// Let's create two people in this array
people[0] = new Person();
people[0].Name = "Jos";
people[0].Age = 30;
people[0].Changed = false;
people[1] = new Person();
people[1].Name = "Jan";
people[1].Age = 25;
people[1].Changed = false;
// And let's set the model of the view to be that array
dataGridView1.DataSource = people;
dataGridView1.CellEndEdit += new DataGridViewCellEventHandler(dataGridView1_CellEndEdit);
}
void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
{
// This makes the view refresh its currently visible values, by reading
// them from the model again. This callback happens after the user is
// done editing a cell.
dataGridView1.Refresh();
}
}
public class Person {
private string name, city;
private uint age;
private bool changed;
public string Name {
get { return name; }
set { name = value; }
}
public bool Changed {
get { return changed; }
set { changed = value; }
}
public uint Age {
get { return age; }
set {
age = value;
Changed = true;
}
}
public string City {
get { return city; }
set { city = value; }
}
}
You can compare a GtkTreeModel with a DataTable in .NET: it’s a model that has its own memory storage and it contains both rows and columns. This means that GtkTreeModel isn’t a generic model, like IList in .NET actually is. With GtkTreeModel you must always represent your data as rows and columns. Even if the data ain’t rows and columns.
I indeed believe that Microsoft got databinding right in their .NET platform, and that Gtk+’s GtkTreeView and GtkTreeModel got it wrong.
Also feel free to have a huge array of Person instances. It’ll only read property values of the visible ones (plus a few more, shouldn’t be much). Fun tip: write something to the console in the property getters of the Person class, and start scrolling. Now you can easily discover yourself how to do lazy loading tricks with MVC in .NET, and make things scale.