I have several methods all with the same parameter types and return values but different names and blocks. I want to pass the name of the method to run to another method that will invoke the passed method.
public int Method1(string)
{
// Do something
return myInt;
}
public int Method2(string)
{
// Do something different
return myInt;
}
public bool RunTheMethod([Method Name passed in here] myMethodName)
{
// Do stuff
int i = myMethodName("My String");
// Do more stuff
return true;
}
public bool Test()
{
return RunTheMethod(Method1);
}
This code does not work but this is what I am trying to do. What I don't understand is how to write the RunTheMethod code since I need to define the parameter.
You can use the Func delegate in .NET 3.5 as the parameter in your RunTheMethod method. The Func delegate allows you to specify a method that takes a number of parameters of a specific type and returns a single argument of a specific type. Here is an example that should work:
public class Class1
{
public int Method1(string input)
{
//... do something
return 0;
}
public int Method2(string input)
{
//... do something different
return 1;
}
public bool RunTheMethod(Func<string, int> myMethodName)
{
//... do stuff
int i = myMethodName("My String");
//... do more stuff
return true;
}
public bool Test()
{
return RunTheMethod(Method1);
}
}
You need to use a delegate. In this case all your methods take a string parameter and return an int - this is most simply represented by the Func<string, int> delegate1. So your code can become correct with as simple a change as this:
public bool RunTheMethod(Func<string, int> myMethodName)
{
// ... do stuff
int i = myMethodName("My String");
// ... do more stuff
return true;
}
Delegates have a lot more power than this, admittedly. For example, with C# you can create a delegate from a lambda expression, so you could invoke your method this way:
RunTheMethod(x => x.Length);
That will create an anonymous function like this:
// The <> in the name make it "unspeakable" - you can't refer to this method directly
// in your own code.
private static int <>_HiddenMethod_<>(string x)
{
return x.Length;
}
and then pass that delegate to the RunTheMethod method.
You can use delegates for event subscriptions, asynchronous execution, callbacks - all kinds of things. It's well worth reading up on them, particularly if you want to use LINQ. I have an article which is mostly about the differences between delegates and events, but you may find it useful anyway.
1 This is just based on the generic Func<T, TResult> delegate type in the framework; you could easily declare your own:
public delegate int MyDelegateType(string value)
and then make the parameter be of type MyDelegateType instead.
From OP's example:
public static int Method1(string mystring)
{
return 1;
}
public static int Method2(string mystring)
{
return 2;
}
You can try Action Delegate! And then call your method using
public bool RunTheMethod(Action myMethodName)
{
myMethodName(); // note: the return value got discarded
return true;
}
RunTheMethod(() => Method1("MyString1"));
Or
public static object InvokeMethod(Delegate method, params object[] args)
{
return method.DynamicInvoke(args);
}
Then simply call method
Console.WriteLine(InvokeMethod(new Func<string,int>(Method1), "MyString1"));
Console.WriteLine(InvokeMethod(new Func<string, int>(Method2), "MyString2"));
In order to provide a clear and complete answer, I'm going to start from the very beginning before showing three possible solutions.
A brief introduction
All .NET languages (such as C#, F#, and Visual Basic) run on top of the Common Language Runtime (CLR), which is a VM that runs code in the Common Intermediate Language (CIL), which is way higher level than machine code. It follows that methods aren't Assembly subroutines, nor are they values, unlike functional languages and JavaScript; rather, they're symbols that CLR recognizes. Not being values, they cannot be passed as a parameter. That's why there's a special tool in .NET. That is, delegates.
What's a delegate?
A delegate represents a handle to a method (the term handle is to be preferred over pointer as the latter would be an implementation detail). Since a method is not a value, there has to be a special class in .NET, namely Delegate, which wraps up any method. What makes it special is that, like very few classes, it needs to be implemented by the CLR itself and couldn't be simply written as a class in a .NET language.
Three different solutions, the same underlying concept
The type–unsafe way
Using the Delegate special class directly.
Example:
static void MyMethod()
{
Console.WriteLine("I was called by the Delegate special class!");
}
static void CallAnyMethod(Delegate yourMethod)
{
yourMethod.DynamicInvoke(new object[] { /*Array of arguments to pass*/ });
}
static void Main()
{
CallAnyMethod(MyMethod);
}
The drawback here is your code being type–unsafe, allowing arguments to be passed dynamically, with no constraints.
The custom way
Besides the Delegate special class, the concept of delegates spreads to custom delegates, which are declarations of methods preceded by the delegate keyword. They are type–checked the same way as “normal” method invocations, making for type-safe code.
Example:
delegate void PrintDelegate(string prompt);
static void PrintSomewhere(PrintDelegate print, string prompt)
{
print(prompt);
}
static void PrintOnConsole(string prompt)
{
Console.WriteLine(prompt);
}
static void PrintOnScreen(string prompt)
{
MessageBox.Show(prompt);
}
static void Main()
{
PrintSomewhere(PrintOnConsole, "Press a key to get a message");
Console.Read();
PrintSomewhere(PrintOnScreen, "Hello world");
}
The standard library's way
Alternatively, you can stick with a delegate that's part of the .NET Standard:
Action wraps up a parameterless void method;
Action<T1> wraps up a void method with one parameter of type T1;
Action<T1, T2> wraps up a void method with two parameters of types T1 and T2, respectively,
and so forth;
Func<TR> wraps up a parameterless function with TR return type;
Func<T1, TR> wraps up a function with TR return type and with one parameter of type T1;
Func<T1, T2, TR> wraps up a function with TR return type and with two parameters of types T1 and T2, respectively;
and so forth.
However, bear in mind that by using predefined delegates like these, parameter names won't be self-describing, nor is the name of the delegate type meaningful as to what instances are supposed to do. Therefore, refrain from using them in contexts where their purpose is not absolutely self-evident.
The latter solution is the one most people posted. I'm also mentioning it in my answer for the sake of completeness.
The solution involves Delegates, which are used to store methods to call. Define a method taking a delegate as an argument,
public static T Runner<T>(Func<T> funcToRun)
{
// Do stuff before running function as normal
return funcToRun();
}
Then pass the delegate on the call site:
var returnValue = Runner(() => GetUser(99));
You should use a Func<string, int> delegate, that represents a function taking a string argument and returning an int value:
public bool RunTheMethod(Func<string, int> myMethod)
{
// Do stuff
myMethod.Invoke("My String");
// Do stuff
return true;
}
Then invoke it this way:
public bool Test()
{
return RunTheMethod(Method1);
}
While the accepted answer is absolutely correct, I would like to provide an additional method.
I ended up here after doing my own searching for a solution to a similar question.
I am building a plugin driven framework, and as part of it I wanted people to be able to add menu items to the applications menu to a generic list without exposing an actual Menu object because the framework may deploy on other platforms that don't have Menu UI objects. Adding general info about the menu is easy enough, but allowing the plugin developer enough liberty to create the callback for when the menu is clicked was proving to be a pain. Until it dawned on me that I was trying to re-invent the wheel and normal menus call and trigger the callback from events!
So the solution, as simple as it sounds once you realize it, eluded me until now.
Just create separate classes for each of your current methods, inherited from a base if you must, and just add an event handler to each.
Here is an example Which can help you better to understand how to pass a function as a parameter.
Suppose you have Parent page and you want to open a child popup window. In the parent page there is a textbox that should be filled basing on child popup textbox.
Here you need to create a delegate.
Parent.cs
// declaration of delegates
public delegate void FillName(String FirstName);
Now create a function which will fill your textbox and function should map delegates
//parameters
public void Getname(String ThisName)
{
txtname.Text=ThisName;
}
Now on button click you need to open a Child popup window.
private void button1_Click(object sender, RoutedEventArgs e)
{
ChildPopUp p = new ChildPopUp (Getname) //pass function name in its constructor
p.Show();
}
IN ChildPopUp constructor you need to create parameter of 'delegate type' of parent //page
ChildPopUp.cs
public Parent.FillName obj;
public PopUp(Parent.FillName objTMP)//parameter as deligate type
{
obj = objTMP;
InitializeComponent();
}
private void OKButton_Click(object sender, RoutedEventArgs e)
{
obj(txtFirstName.Text);
// Getname() function will call automatically here
this.DialogResult = true;
}
If you want to pass Method as parameter, use:
using System;
public void Method1()
{
CallingMethod(CalledMethod);
}
public void CallingMethod(Action method)
{
method(); // This will call the method that has been passed as parameter
}
public void CalledMethod()
{
Console.WriteLine("This method is called by passing it as a parameter");
}
If the method passed needs to take one argument and return a value, Func is the best way to go. Here is an example.
public int Method1(string)
{
// Do something
return 6;
}
public int Method2(string)
{
// Do something different
return 5;
}
public bool RunTheMethod(Func<string, int> myMethodName)
{
// Do stuff
int i = myMethodName("My String");
Console.WriteLine(i); // This is just in place of the "Do more stuff"
return true;
}
public bool Test()
{
return RunTheMethod(Method1);
}
Read the docs here
However, if your method that is passed as a parameter does not return anything, you can also use Action. It supports up to 16 paramaters for the passed method. Here is an example.
public int MethodToBeCalled(string name, int age)
{
Console.WriteLine(name + "'s age is" + age);
}
public bool RunTheMethod(Action<string, int> myMethodName)
{
// Do stuff
myMethodName("bob", 32); // Expected output: "bob's age is 32"
return true;
}
public bool Test()
{
return RunTheMethod(MethodToBeCalled);
}
Read the documentation here
Here is an example without a parameter:
http://en.csharp-online.net/CSharp_FAQ:_How_call_a_method_using_a_name_string
with params:
http://www.daniweb.com/forums/thread98148.html#
you basically pass in an array of objects along with name of method. you then use both with the Invoke method.
params Object[] parameters
class PersonDB
{
string[] list = { "John", "Sam", "Dave" };
public void Process(ProcessPersonDelegate f)
{
foreach(string s in list) f(s);
}
}
The second class is Client, which will use the storage class. It has a Main method that creates an instance of PersonDB, and it calls that object’s Process method with a method that is defined in the Client class.
class Client
{
static void Main()
{
PersonDB p = new PersonDB();
p.Process(PrintName);
}
static void PrintName(string name)
{
System.Console.WriteLine(name);
}
}
I don't know who might need this, but in case you're unsure how to send a lambda with a delegate, when the function using the delegate doesn't need to insert any params in there you just need the return value.
SO you can also do this:
public int DoStuff(string stuff)
{
Console.WriteLine(stuff);
}
public static bool MethodWithDelegate(Func<int> delegate)
{
///do stuff
int i = delegate();
return i!=0;
}
public static void Main(String[] args)
{
var answer = MethodWithDelegate(()=> DoStuff("On This random string that the MethodWithDelegate doesn't know about."));
}
I see code written like this:
static void Main(string[] args)
{
var name = GetInfo(); //this variable contains the method below
Console.Writeline(name)
}
static string GetInfo()
{
string name = "MyName";
return (name);
}
Let's use the typical box example. What's a good example for method inside it?
In other words, what does it mean 'a value' = 'a method that does something'
Its not assigning a method, it is just getting the result of that executed method. In this way you can reuse GetInfo(); in other places where ever you need this name.
I want to store a method call in an action. That method is a static method, but with a string argument that varies. So I want to store "call StaticMethod with argument "myString" in an Action.
But... without capturing this.
I can store an anonymous method () => StaticMethod(myString) in the action , but this captures the action target (this). (Edit: it doesn't. See the accepted answer).
I can store the static method in the action, but then I'm missing the argument.
I could store the static method and the arguments separately, but due to technical reasons, this is cumbersome and ugly.
Do I have any other possibility?
[Edit]
In other words, I want to do this:
private void MyMethod(string myString){
var action = Call StaticMethod with argument myString.
}
And somewhere else, where I have access to action, but don't know anything about the string, or that there are arguments:
action.Invoke();
action can capture the string, but can't capture this (the call target of MyMethod).
Given the following assumptions:
myString is a local variable, or a parameter to the method (Not! a property or field)
StaticMethod is really a static method
There are no other delegates being constructed in the same method as you want to construct action
then the following:
public void M() {
string myString = "something";
Action action = () => StaticMethod(myString);
}
public static void StaticMethod(string value) { }
will be compiled as this:
[CompilerGenerated]
private sealed class <>c__DisplayClass0_0
{
public string myString;
internal void <M>b__0()
{
StaticMethod(myString);
}
}
public void M()
{
<>c__DisplayClass0_0 <>c__DisplayClass0_ = new <>c__DisplayClass0_0();
<>c__DisplayClass0_.myString = "something";
Action action = new Action(<>c__DisplayClass0_.<M>b__0);
}
As you can see, your lambda is lifted out to a generated display class, and myString is also lifted out from your method, going from a local variable to a field on that display class. This is the closure, and the object constructed in the M method will be the target of the action, and this closure will not capture this.
You can see this in action here: SharpLab
Note that small changes to your code will invalidate this as the assumptions change. For instance, if you also, in the same method, declare another delegate that also requires a closure and also requires access to this, then the same closure will be shared between the two delegates.
Example:
public void M() {
string myString = "something";
Action action = () => StaticMethod(myString);
Action otherAction = () => StaticMethod(Property);
}
public string Property => "Value";
Generates this code:
[CompilerGenerated]
private sealed class <>c__DisplayClass0_0
{
public string myString;
public C <>4__this;
internal void <M>b__0()
{
StaticMethod(myString);
}
internal void <M>b__1()
{
StaticMethod(<>4__this.Property);
}
}
public string Property
{
get
{
return "Value";
}
}
public void M()
{
<>c__DisplayClass0_0 <>c__DisplayClass0_ = new <>c__DisplayClass0_0();
<>c__DisplayClass0_.<>4__this = this;
<>c__DisplayClass0_.myString = "something";
Action action = new Action(<>c__DisplayClass0_.<M>b__0);
Action action2 = new Action(<>c__DisplayClass0_.<M>b__1);
}
As you can see, the same closure is used to support both delegates, and now both delegates has a reference to a closure that captures this.
If you can't define your action at call site at compile time e.:
Action a = () => StaticMethod("myString");
Then you will probably want to use expressions for this.
Example Code:
[Fact]
public void SampleActionWithoutThisScopeTests()
{
// Using Compile Time Action
Action compileTimeAction = () => MyStaticMethod("CompileTime myString");
compileTimeAction.Invoke();
// Using Compiled Expression
var myString = "Expression myString";
var methodInfo = this.GetType().GetMethod(nameof(MyStaticMethod), BindingFlags.Static | BindingFlags.Public);
var stringArgumentConstant = Expression.Constant(myString);
var callExpression = Expression.Call(null, methodInfo, stringArgumentConstant);
var lambda = Expression.Lambda<Action>(callExpression);
var action = lambda.Compile();
action.Invoke();
}
public static void MyStaticMethod(string input)
{
Console.WriteLine(input);
}
EDIT
If you can, and meet the requirements for the compiler-generated closure to not contain "this" via normal lambda syntax (see #Lasse V. Karlsen answer, then definitely use that approach!
I know a refactor safe way to get the name of a property with this answer. Is there a refactor safe way to get the name of a method?
I am using C# 5 and .Net 4.5.
To illustrate what I'm trying to do:
class MyClass
{
public void UnitTestOne() { /* impl */ }
public void UnitTestTwo() { /* impl */ }
public void UnitTestThree()
{
//I'd like to get the method names for UnitTestOne and UnitTestTwo here
//in such a way that this code will raise a compile time error if either
//the UnitTestOne or UnitTestTwo method names changes.
}
}
UPDATE: Here is a nice post that explains and provides a flexible utility method to access MethodInfos with refactor safe code. http://www.codeducky.org/10-utilities-c-developers-should-know-part-two/
I think Jon Skeet's answer is fine if you only want to cover void parameterless methods. A more general solution would look like this:
public class MyClass
{
public void UnitTestOne(int i) { /* impl */ }
public int UnitTestTwo() { /* impl */ }
public void UnitTestThree()
{
var methodCallExpressions = new Expression<Action<MyClass>>[] {
mc => mc.UnitTestOne(default(int)), //Note that a dummy argument is provided
mc => mc.UnitTestTwo()
};
var names = methodCallExpressions.Select(mce =>
((MethodCallExpression) mce.Body).Method.Name);
}
}
Note that we use an array of Expression<Action<MyClass>> in order to make a list of method calls on MyClass without knowing the return type and parameter types of each method call. Each method call expression is provided dummy variables to instantiate the expression.
Then the body of each expression is cast to a MethodCallExpression which, as the type name indicates, holds an expression which is just the calling of a method. That type has a Method property which is the MethodInfo of the method being called.
In the link you provided, a property name is extracted similarly using a MemberExpression. Using MethodCallExpression makes the examples quite similar.
By the way, you can also use Expression<Action> instead of Expression<Action<MyClass>> if you prefer. Replace the methodCallExpressions instantiation with:
var methodCallExpressions = new Expression<Action>[] {
() => this.UnitTestOne(default(int)),
() => this.UnitTestTwo()
};
I see this as mostly a stylistic decision, although it would also allow you to encapsulate method calls on a different class, using something like () => (new MyClass2()).UnitTestThree().
The simplest way is probably just to create a delegate for each method, and use the MulticastDelegate.Method property:
class MyClass
{
public void UnitTestOne() { /* impl */ }
public void UnitTestTwo() { /* impl */ }
public void UnitTestThree()
{
var actions = new Action[] { UnitTestOne, UnitTestTwo };
var names = actions.Select(x => x.Method.Name);
}
}
Is there a way to get a method's name (as a string) by providing the method itself?
class Person
{
bool Eat(Food food){...}
}
I want to somehow get the string "Eat". That's all! This can either be from an instance or from the class declaration using reflection.
My attempt:
public delegate bool EatDelegate(Food f);
EatDelegate eatDel = new EatDelegate(_person1.Eat);
string methodName = eatDel.GetInvocationList()[0].Method.Name;
This requires to know the method's delegate and the whole thing is unreadable
I want the methodName in order to dynamically invoke it.
Notes:
There is a delegate declaration for every method I want to invoke
I want to avoid specifying the method's name in order to avoid errors after reflection etc
The method isn't called the moment I want to get its name. (cannot use MethodBase.GetCurrentMethod() )
I have to use .Net 3.5
public string GetName(Expression<Action> exp)
{
var mce = exp.Body as MethodCallExpression;
return mce.Method.Name;
}
--
a Method
public int MyMethod(int i)
{
return 0;
}
and usage
var s= GetName(()=>this.MyMethod(0));
var methods = typeof(Person).GetMethods();
foreach (var method in methods)
{
if (method.Name.Equals("Eat"))
{
// do something here...
}
}