C#•2y ago

Can anyone explain this piece of code for me please ?

I've just started learning how to use Action in Unity, this seem advanced

4 Replies

First, you need to understand variable that points to a method

static void Print(int x)
{
    Console.WriteLine(x);
}

static void PrintSquare(int x)
{
    Console.WriteLine(x * x);
}

Action<int>? variable_pointing_to_method;

// pointing to Print method
variable_pointing_to_method = Print;

// longer syntax
if (variable_pointing_to_method is not null)
    variable_pointing_to_method(10); // prints 10.

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 10.



// pointing to PrintSquare
variable_pointing_to_method = PrintSquare;

// longer syntax is removed for the sake of simplicity

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 100.

static void Print(int x)
{
    Console.WriteLine(x);
}

static void PrintSquare(int x)
{
    Console.WriteLine(x * x);
}

Action<int>? variable_pointing_to_method;

// pointing to Print method
variable_pointing_to_method = Print;

// longer syntax
if (variable_pointing_to_method is not null)
    variable_pointing_to_method(10); // prints 10.

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 10.



// pointing to PrintSquare
variable_pointing_to_method = PrintSquare;

// longer syntax is removed for the sake of simplicity

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 100.

Second, you need to understand lambda expression.

Action<int>? variable_pointing_to_method;

// pointing to a lambda expression
variable_pointing_to_method = x => Console.WriteLine(x * x * x);

// longer syntax is removed for the sake of simplicity.

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 1000.

Action<int>? variable_pointing_to_method;

// pointing to a lambda expression
variable_pointing_to_method = x => Console.WriteLine(x * x * x);

// longer syntax is removed for the sake of simplicity.

// shorter syntax
variable_pointing_to_method?.Invoke(10); // prints 1000.

The right hand side of the following assignment is a lambda expression.

variable_pointing_to_method = x => Console.WriteLine(x * x * x);

variable_pointing_to_method = x => Console.WriteLine(x * x * x);

You can read x => Console.WriteLine(x * x * x) as a function that takes one argument x of type int and prints the cube of x. Why is the type of x int? Because variable_pointing_to_method is of type Action<int>.

Anu6is•2y ago

to add on to the last part Action<int> expects a method that accepts and int and return nothing aka void method so the lambda x => Console.WriteLine(x * x * x); translates to

static void CubeAndPrint(int x) // void method accepts an int 
{
    Console.WriteLine(x * x * x);
}

static void CubeAndPrint(int x) // void method accepts an int 
{
    Console.WriteLine(x * x * x);
}

🥄feeders help me learn faster !•2y ago

The previous examples show how to create a local variable pointing to methods which can be a lambda expression too. Now we pass the local variable as an argument of ShowRandom(). This argument is called callback because it is called or invoked in ShowRandom().

Action<int>? localvariable= x => Console.WriteLine($"Hello! {x}");
ShowRandom(localvariable);

// or you can also directly pass without local variable.
ShowRandom(x => Console.WriteLine($"Hello! {x}"));

static void ShowRandom(Action<int>? callback)
{
    int rand = Random.Shared.Next(0,10);

    callback?.Invoke(rand);
}

Action<int>? localvariable= x => Console.WriteLine($"Hello! {x}");
ShowRandom(localvariable);

// or you can also directly pass without local variable.
ShowRandom(x => Console.WriteLine($"Hello! {x}"));

static void ShowRandom(Action<int>? callback)
{
    int rand = Random.Shared.Next(0,10);

    callback?.Invoke(rand);
}

The code below is just a trivial wrapping.

ShowCB();

static void ShowCB()
{
    ShowRandom(x => Console.WriteLine($"Hello! {x}"));
}

static void ShowRandom(Action<int>? callback)
{
    int rand = Random.Shared.Next(0,10);

    callback?.Invoke(rand);
}

ShowCB();

static void ShowCB()
{
    ShowRandom(x => Console.WriteLine($"Hello! {x}"));
}

static void ShowRandom(Action<int>? callback)
{
    int rand = Random.Shared.Next(0,10);

    callback?.Invoke(rand);
}

🥄feeders help me learn faster !•2y ago

Another non-trivial example.

// customer can subscribe to notification from kitchen staff
// by providing a callback as follows.
Action<int, int>? customerCallback = (x, y) =>

{
    Console.WriteLine($"Step {x} of {y} has been completed.");
    //other code can go here as well.
};

// customer orders and passes his callback 
await OrderPizza(customerCallback);
// customer gets notified every 1 second.


static async Task OrderPizza(Action<int, int>? callback)
{
    // one pizza usually takes 5 to 10 steps
    // and each step takes about 1 second

    // let simulate the number of steps randomly
    var steps = Random.Shared.Next(5, 11);

    // kitchen staff notifies customer when each step completes by
    for (int i = 0; i < steps; ++i)
    {
        await Task.Delay(1000); // one second delay for simulation purpose
        callback?.Invoke(i + 1, steps);// sending both i+1 and steps variables.
    }
}

// customer can subscribe to notification from kitchen staff
// by providing a callback as follows.
Action<int, int>? customerCallback = (x, y) =>

{
    Console.WriteLine($"Step {x} of {y} has been completed.");
    //other code can go here as well.
};

// customer orders and passes his callback 
await OrderPizza(customerCallback);
// customer gets notified every 1 second.


static async Task OrderPizza(Action<int, int>? callback)
{
    // one pizza usually takes 5 to 10 steps
    // and each step takes about 1 second

    // let simulate the number of steps randomly
    var steps = Random.Shared.Next(5, 11);

    // kitchen staff notifies customer when each step completes by
    for (int i = 0; i < steps; ++i)
    {
        await Task.Delay(1000); // one second delay for simulation purpose
        callback?.Invoke(i + 1, steps);// sending both i+1 and steps variables.
    }
}

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Can anyone explain this piece of code for me please ?

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