Adding Events To A Class

//=====WaterTankEventArgs class in EventProducerLib============
namespace EventProducerLib
{

    public class WaterTankEventArgs
    {
        //contains data to send back to the event handler
        private double _amount;
        private string _message;

        public WaterTankEventArgs(double amount, string message)
        {
            _amount = amount;
            _message = message;
        }

        public double Amount { get { return this._amount; } }
        public string Message { get { return this._message; } }
    }
}
//==================================================
namespace EventProducerLib
{
    //1. Define a delegate type
    public delegate void WaterTankHandler(object sender, WaterTankEventArgs e);

    public class WaterTank
    {
        private double _capacity; // in gallons
        private double _currentAmount; // in gallons

        //this is the producer class
        //it produces (generates) an event
        //An event provides a callback mechanism
        //callback means event producer(class) calls back to window apps
        //producer doesn't know which method to call, that is why it uses delegate to call methods.
        //delegate is reference to methods

        //2. define an event that is raised when WaterTank overflows
        public event WaterTankHandler TankOverflow;
        public event WaterTankHandler TankEmpty;

        public WaterTank(double capacity, double initialAmount)
        {
            _capacity = capacity;
            _currentAmount = initialAmount;
        }

        public double Capacity
        { get { return _capacity; } }
        public double CurrentAmount
        { get { return _currentAmount; } }

        public void AddWater(double amount)
        {
            if (_currentAmount + amount > _capacity)
            {
                //notify the user of this class thru an event

                //3. add code to raise / fire the Tankoverflow
                if (TankOverflow != null)
                {
                    WaterTankEventArgs e = new WaterTankEventArgs(_currentAmount, "Tank will exceed capacity, Re-enter new amount");
                    TankOverflow(this, e);
                }
            }
            else

            _currentAmount += amount;
        }

        public void RemoveWater(double amount)
        {
            if (_currentAmount - amount < 0)
            {
                //notify user, thru an event
                if (TankEmpty != null) //**********************************
                {
                    WaterTankEventArgs et = new WaterTankEventArgs(_currentAmount, "You do not have enough water to remove, Re-enter new amount");
                    TankEmpty(this, et);
                }
            }
            else
            _currentAmount -= amount;
        }
    }
}
//=====================================================
using System.Windows.Forms;
using EventProducerLib; //Added to work class library

namespace AddingEventsToAClass
{
    //Use a class that defines an event
    //have the class fire an event
    //have this form consume the event => listening to an event
    //means providing a method (event handler) that gets called when the event occurs
    //(meaning when the event is fired)

    public partial class Form1 : Form
    {
        WaterTank wt = null;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            groupBox2.Enabled = false;
        }

        //TankOverFlow method handler
        private void wt_TankOverflow(object sender, WaterTankEventArgs e)
        {
            MessageBox.Show("Current amount: " + e.Amount + "\n" + e.Message);
        }

        //TankEmpty method handler
        private void wt_TankEmpty(object sender, WaterTankEventArgs et)
        {
            MessageBox.Show("Current amount: " + et.Amount + "\n" + et.Message);
        }

        private void btnCreateWaterTank_Click(object sender, EventArgs e)
        {
            try
            {
                double capacity = double.Parse(txtCapacity.Text);
                double initialAmt = double.Parse(txtInitialAmount.Text);

                if (initialAmt <= capacity)
                {
                    //Create water tank
                    wt = new WaterTank(capacity, initialAmt);

                    //attach the TankOverFlow event handler

                    //register to listen to the TankOverFlow event
                    //1. Create a delegate object from the delegate type defined in the WaterTank class 
                    //old fashion way
                    //WaterTankHandler wth = wt_TankOverflow;
                    //wt.TankOverflow += wth;

                    //this is a shortcut to link method with delegate
                    wt.TankOverflow += wt_TankOverflow;
                   
                    wt.TankEmpty += wt_TankEmpty;


                    //disable create, enable other functions
                    groupBox1.Enabled = false;
                    groupBox2.Enabled = true;
                }
                else
                {
                    MessageBox.Show("Initial gallons amount cannot exceed capacity");
                    txtCapacity.Clear();
                    txtInitialAmount.Clear();
                }
            }
            catch (FormatException fe)
            {
                MessageBox.Show(fe.Message);
            }
        }

        private void btnAddWater_Click(object sender, EventArgs e)
        {
            try
            {
                double amount = double.Parse(txtWaterGtoAorR.Text);
                //add amount to the tank wt
                wt.AddWater(amount);
                lblCurrentLevel.Text = "Current Amount  = " + wt.CurrentAmount;
            }
            catch (FormatException fe)
            {
                MessageBox.Show(fe.Message);
            }

        }

        private void btnRemoveWater_Click(object sender, EventArgs e)
        {
            try
            {
                double amount = double.Parse(txtWaterGtoAorR.Text);
                //add amount to the tank wt
                wt.RemoveWater(amount);
                lblCurrentLevel.Text = "Current Amount  = " + wt.CurrentAmount;
            }
            catch (FormatException fe)
            {
                MessageBox.Show(fe.Message);
            }
        }
    }
}
///Assignment:
///Define a second event TankEmpty (below zero)
///Fire it in the remove  water method
///Register this event in the Form
///Demonstrate that it works