Tim Van Wassenhove

Sometimes you want to manipulate the order in which properties are used for databinding. Eg: If you drag and drop an object datasource on a DataGridView you have no control in which order it binds the properties. Offcourse, you can order the columns by moving them around… Today someone asked the following:

I would like to have it come from the class in the order I want it. Any suggestions on how to set the display order without referencing the actual member names?

I started with the implementation of a PropertyOrderAttribute:

[AttributeUsage(AttributeTargets.Property)]
public class PropertyOrderAttribute : Attribute
{
 private int order;

 public PropertyOrderAttribute(int order)
 {
  this.order = order;
 }

 public int Order
 {
  get { return this.order; }
 }
}

So the user can use this attribute to define the order in which the properties should appear as following:

class Foo
{
 private int id;
 private string name;
 private DateTime birthDay;

 public Foo(int id, string name, DateTime birthDay)
 {
  this.id = id;
  this.name = name;
  this.birthDay = birthDay;
 }

 [PropertyOrder(0)]
 public int Id
 {
  get { return id; }
  set { id = value; }
 }

 [PropertyOrder(2)]
 public string Name
 {
  get { return name; }
  set { name = value; }
 }

 [PropertyOrder(1)]
 public DateTime BirthDay
 {
  get { return birthDay; }
  set { birthDay = value; }
 }
}

And now i implement a generic BindingList that makes use of the PropertyOrderAttributes:

class PropertyOrderBindingList<t> : BindingList<t>, ITypedList
{
 public PropertyOrderBindingList()
  : base()
 {
  //
 }

 public PropertyDescriptorCollection GetItemProperties(PropertyDescriptor[] listAccessors)
 {
  PropertyDescriptorCollection typePropertiesCollection = TypeDescriptor.GetProperties(typeof(T));
  return typePropertiesCollection.Sort(new PropertyDescriptorComparer());
 }

 public string GetListName(PropertyDescriptor[] listAccessors)
 {
  return string.Format("A list with Properties for {0}", typeof(T).Name);
 }
}

class PropertyDescriptorComparer : IComparer
{
 public int Compare(object x, object y)
 {
  if (x == y) return 0;
  if (x == null) return 1;
  if (y == null) return -1;

  PropertyDescriptor propertyDescriptorX = x as PropertyDescriptor;
  PropertyDescriptor propertyDescriptorY = y as PropertyDescriptor;

  PropertyOrderAttribute propertyOrderAttributeX = propertyDescriptorX.Attributes[typeof(PropertyOrderAttribute)] as PropertyOrderAttribute;
  PropertyOrderAttribute propertyOrderAttributeY = propertyDescriptorY.Attributes[typeof(PropertyOrderAttribute)] as PropertyOrderAttribute;

  if (propertyOrderAttributeX == propertyOrderAttributeY) return 0;
  if (propertyOrderAttributeX == null) return 1;
  if (propertyOrderAttributeY == null) return -1;

  return propertyOrderAttributeX.Order.CompareTo(propertyOrderAttributeY.Order);
 }
}

With all this infrastructure it becomes as easy as:

public Form1()
{
 InitializeComponent();

 PropertyOrderBindingList<foo> fooList = new PropertyOrderBindingList<foo>();
 fooList.Add(new Foo(1, "Timvw", new DateTime(1980, 4, 30)));
 fooList.Add(new Foo(2, "Mike", new DateTime(1984, 1, 1)));
 this.dataGridView1.DataSource = fooList;
}