Custom Binding with INotifyPropertyChanged Interface

Introduction

In this post I would like to show a simple example of using INotifyPropertyChanged interface for binding a custom object properties to WinForm controls.

According to Microsoft's documentation INotifyPropertyChanged interface is used to notify clients about properties value changes.

The underneath idea is very simple: implementing this interface, forces raising PropertyChange event, which in-turn notifies client that binded property has changed.

The Example

Let's start with building a simple BankAccount class :

public class BankAccount : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private decimal m_Balance;
        private decimal m_CreditLimit;

        public BankAccount(decimal initialBalance)
        {
            this.m_Balance = initialBalance;
            this.m_CreditLimit = initialBalance * 2;
        }

        public decimal Balance
        {
            get { return m_Balance; }
        }

        public decimal CreditLimit
        {
            get { return m_CreditLimit; }
        }

        public void Withdrawal(decimal sum)
        {
            if (sum <= m_Balance) 
            { 
                m_Balance -= sum; 
                if (PropertyChanged != null) 
                { 
                    PropertyChanged(this, 
                       new PropertyChangedEventArgs("Balance")); 
                } 
            }
        }

        public void Deposit(decimal sum)
        {
            if (sum > 0)
            {
                m_Balance += sum;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, 
                       new PropertyChangedEventArgs("Balance"));
                }

                if(m_Balance >= m_CreditLimit)
                {
                    m_CreditLimit = m_Balance * 2;
                    if (PropertyChanged != null)
                    {
                        PropertyChanged(this, 
                          new PropertyChangedEventArgs("CreditLimit"));
                    }
                }
            }
        }

    }

The class contains two properties "Balance" and "CreditLimit" which are going to be binded to our simple UI elements:

Here is the code demonstrating how we actually bind it:

public partial class MainForm : Form
{
    private BankAccount m_Account;

    public MainForm()
    {
       InitializeComponent();
       m_Account = new BankAccount(1000);

       BindControls();
    }

    private void BindControls()
    {
        txtBalance.DataBindings.Add("Text",
                               m_Account,
                               "Balance",
                               true,
                               DataSourceUpdateMode.OnPropertyChanged);

       txtCreditLimit.DataBindings.Add("Text",
                                  m_Account,
                                  "CreditLimit",
                                  true,
                                  DataSourceUpdateMode.OnPropertyChanged);
    } 

    private void btnWithdrawal_Click(object sender, EventArgs e)
    {
        m_Account.Withdrawal(decimal.Parse(txtSum.Text));
    }

    private void btnDeposit_Click(object sender, EventArgs e)
    {
        m_Account.Deposit(decimal.Parse(txtSum.Text));
    }
 }

Now, the binded textboxes will automatically reflect changes of "Balance" and "CreditLimit" properties after calling Withdrawal/Deposit methods:

The working example could be downloaded here.

This is it,

Mark