Data binding = "automatic way of setting any run-time accessible property of any control on a form" [MS]

Two kinds:

• simple - bind to a single data element. Example: the Text property of a TextBox.
• complex - bind to more than one data element. = list-based binding. DataGridView, ListBox, ComboBox.

There are many kinds of sources for data binding. You can bind to:

• a simple object
• an array or list (need to support IList, but IBindingList/BindingList is better because of 2-way support)
• IEnumerable (via a BindingSource)
• ADO.NET data objects
  • DataColumn
  • DataTable (actually binds to the DefaultView)
  • DataView
  • DataSet (actually binds to the DataViewManager)
  • DataViewManager

But the thing you really want to bind to for most situations is a BindingSource.

• New in .Net 2.0.
• Typical use: bind controls to a BindingSource and the BindingSource to a DataTable.
  • This provides indirection that can be useful.
• We also get:
  • currency management = keeping track of the current record/item
  • change notification

Really, we will want to do all our work using BindingSource.

However, the example below shows how to do simple data-binding to text boxes by hand. You could do this in .Net 1.x. Code is in my example VS\BasicDataBinding.

In this example:

• There is a simple class Student. Public properties are Name, Grade, GradeColor.
• We create one instance of Student, stored in the instance variable m_student.
• On the form, there are two text boxes.
  • txtName: we data-bind its Text property to the Name field of a specific student.
  • txtGrade: we data-bind its Text property to the Grade field of the student, and its BackColor property to the GradeColor property
• We also bind a text box to an array of strings.
• Two buttons allow navigation through the list.
• The button code shows two ways to get the BindingManager for the animal list.
  • from the specific Binding at the control level
  • from the BindingContext at the form level
• BindingManagerBase is the abstract base class for
  • PropertyMananger = used for an item data source
  • CurrencyManager = used for a list data source.

    public class Student
    {
        public Student() { name = string.Empty; grade = 0; }
        public Student ( string name, int grade)
        {
            this.name = name;
            this.grade = grade;
        }

        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }
        private int grade;

        public int Grade
        {
            get { return grade; }
            set { grade = value; }
        }

        public Color GradeColor
        {
            get { return grade >= 90 
                ? Color.Green 
                : grade >= 80 
                ? Color.Yellow 
                : grade >= 70 
                ? Color.Orange 
                : Color.Red; }
        }

        public override string ToString()
        {
            return String.Format("[{0} {1} {2}]",
                name, grade, GradeColor);
        }
    }

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        Student m_student = new Student("Fred", 95);

        string[] m_animals = { "lions", "tigers", "bears", "pandas", "voles" };


        private void Form1_Load(object sender, EventArgs e)
        {
            txtName.DataBindings.Add("Text", m_student, "Name");
            txtGrade.DataBindings.Add("Text", m_student, "Grade");
            txtGrade.DataBindings.Add("BackColor", m_student, "GradeColor");

            txtAnimal.DataBindings.Add("Text", m_animals, null);
        }

        private void btnReport_Click(object sender, EventArgs e)
        {
            MessageBox.Show(m_student.ToString());
        }

        private void btnNext_Click(object sender, EventArgs e)
        {
            BindingManagerBase mgr = this.BindingContext[m_animals];
            ++mgr.Position;
        }

        private void btnPrev_Click(object sender, EventArgs e)
        {
            Binding binding = txtAnimal.DataBindings["Text"];
            BindingManagerBase mgr = binding.BindingManagerBase;
            --mgr.Position;
        }
    }