C# Action Delegate

Action is a delegate type defined in the System namespace. The Action type delegate is the same as the Func delegate, except that the Action delegate does not return a value. In other words, the Action delegate can be used with methods that have a void return type.

What is the Action generic delegate

Action<T> is a built-in generic delegate in .NET Framework, which can be used to pass methods as parameters with the Action<T> delegate without explicitly declaring a custom delegate. The enclosed method must correspond to the method signature defined by the delegate. That is, the enclosed method must have a parameter passed to it by value and cannot have a return value.

For example, the following delegate prints an int value.

public delegate void Print(int val);
static void ConsolePrint(int i)
{
　　　　Console.WriteLine(i);
}
static void Main(string[] args)
{　　　　　　　　　　　
　　　　Print prnt = ConsolePrint;
　　　　prnt(10);
}

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You can use the Action delegate instead of the defined Print delegate, for example:

static void ConsolePrint(int i)
{
　　　　Console.WriteLine(i);
}
static void Main(string[] args)
{
　　　　Action<int> printActionDel = ConsolePrint;
　　　　printActionDel(10);
}

You can use the new keyword or directly assign a method to initialize the Action delegate:

Action<int> printActionDel = ConsolePrint;
//or
Action<int> printActionDel = new Action<int>(ConsolePrint);

The Action delegate can accept at most16different types of input parameters.

Action delegate and anonymous method

You can also assign an anonymous method to an Action delegate, for example:

static void Main(string[] args)
{
　　　　Action<int> printActionDel = delegate(int i)
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　{
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Console.WriteLine(i);
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　};
　　　　printActionDel(10);
}

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Action delegate and Lambda expression

Lambda expressions can also be used with Action delegates:

static void Main(string[] args)
{
　　　　Action<int> printActionDel = i => Console.WriteLine(i);
　　　　　　　
　　　　printActionDel(10);
}

Therefore, you can use any method that does not return an Action delegate type.

Example of using the Action delegate

• The Action delegate can accept at least 0 and at most16parameters, and no return value.

• The Action represents a delegate with no parameters and no return value.

• The Action<int, string> represents a delegate with input parameters int, string and no return value.

• The Action<int, string, bool> represents a delegate with input parameters int, string, bool and no return value.

• Action<int, int, int, int> indicates that there are four input parameters.4an int parameter, a delegate with no return value.

Advantages of Action and Func delegates

1. Define delegates easily and quickly.

2. Make the code concise.

3. compatible types throughout the entire application.