What is Action?

问题:

What is Action<string>, how can it be used?

回答1:

Action is a standard delegate that has one to 4 parameters (16 in .NET 4) and doesn't return value. It's used to represent an action.

Action<String> print = (x) => Console.WriteLine(x);

List<String> names = new List<String> { "pierre", "paul", "jacques" };
names.ForEach(print);

There are other predefined delegates :

• Predicate, delegate that has one parameter and returns a boolean.

  Predicate<int> predicate = ((number) => number > 2);
  var list = new List<int> { 1, 1, 2, 3 };
  var newList = list.FindAll(predicate);
  

• Func is the more generic one, it has 1 to 4 parameters (16 in .NET 4) and returns something

回答2:

This is a delegate to a function with the signature void Bla(string parameter). You can use this to pass functions to other functions. For instance you can do this

Action<string> action = (x => Console.WriteLine(x));
new List<string>{"1","2","3"}.ForEach(action);

to print all characters to the console

回答3:

It is a delegate with one parameter, this being a string.

Usefull because it means you do not have to create delegates anymore for actions as long as you can use a standard action for them (i.e. the number of parameters is fixed, no default values and you can just use an existing action).

回答4:

public void ValidateInput(string input)
{
   //some code
}

public void test()
{
   Action<string> action = ValidateInput;
}

回答5:

It is basically just a delegate that does not return a value.

Have a look here: http://msdn.microsoft.com/en-us/library/018hxwa8.aspx

Action<string> would just be a delegate of a method that excepted a single string parameter and did not return anything.

回答6:

here is a small and easy introduction of Action:

http://www.c-sharpcorner.com/UploadFile/rmcochran/anonymousMethods04022006141542PM/anonymousMethods.aspx