Understanding Lambda Expressions

Of all the additions to the C# language, lambda expressions are potentially the most confusing. Part of this might be due to the odd look of the syntax when you first see it or that a lot of the examples use single letters in the expressions.

The best way to start thinking about lambdas is to think of them simply as anonymous methods.

Suppose we have declared a Timer in a WinForms application as: Timer t = new Timer(); We now need to wire up the Timer's Tick event to some code that is to be executed when the Timer fires.

There are various ways to do this without using lambdas:

  1. Declare an explicit event handler method

    void t_Tick(object sender, EventArgs e)
    {
        textBox1.Text = DateTime.Now.ToString();
    }

    ...
    t.Tick +=new EventHandler(t_Tick); or using delegate inference t.Tick += t_Tick;

  2. Use an anonymous method

    t.Tick += delegate(object sender2, EventArgs e2)
    {
       textBox1.Text = DateTime.Now.ToString();
    };


To write the above using a lambda expression you could write:

t.Tick += (object sender2, EventArgs e2) => textBox1.Text = DateTime.Now.ToString();

Or using type inference:

t.Tick += (sender2, e2) => textBox1.Text = DateTime.Now.ToString(); 

These are examples of expression lambdas. Another type is the statement lambda which is similar but can contain multiple statements enclosed in braces; for example we could write the following:

t.Tick += (object sender2, EventArgs e2) =>
{
    textBox1.Text = DateTime.Now.Minute.ToString();
    textBox2.Text = DateTime.Now.Second.ToString();
};

Note: the => is typically read as "goes to".

Another Example

To print all numbers in a list of ints to a TextBox:

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
numbers.ForEach(number => textBox1.Text += number.ToString());

To print all number from 6 and up:

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
numbers.ForEach(number =>
{
    if (number > 5)
        textBox1.Text += number;
});

or:

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
numbers.FindAll(number => number > 5).ForEach(number => textBox1.Text += number.ToString());

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