Pass Method as Parameter using C

Question

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  quot My String quot           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

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You should use a Func lt string  int gt  delegate  that represents a function taking a string argument and returning an int value  public bool RunTheMethod Func lt string  int gt  myMethod           Do stuff     myMethod Invoke  quot My String quot           Do stuff     return true     Then invoke it this way  public bool Test         return RunTheMethod Method1

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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

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In order to provide a clear and complete answer  I m going to start from the very beginning before coming up with three possible solutions   A brief introduction All languages that run on top of the CLR  Common Language Runtime   such as C   F   and Visual Basic  work under a VM that runs higher level code than machine code  which native languages like C and C   are compiled to  It follows that methods aren t Assembly subroutines  nor are they values  unlike JavaScript as well as most functional languages  rather  they re definitions that CLR recognizes  Thus  you cannot think to pass a method as a parameter  because methods don t produce any values themselves  as they re not expressions but statements  which are stored in the generated assemblies  At this point  you ll face delegates   What s a delegate  A delegate represents a handle to a method  the term handle is to be preferred over pointer as it is implementation   dependent   As I said above  a method is not a value  hence there s a special class in CLR languages  namely Delegate  which wraps up any method  Look at the following example  static void MyMethod         Console WriteLine  quot I was called by the Delegate special class  quot       static void CallAnyMethod Delegate yourMethod        yourMethod DynamicInvoke new object       Array of arguments to pass          static void Main         CallAnyMethod MyMethod       Three different solutions  the same underlying concept   The type   unsafe way Using the Delegate special class directly the same way as the example above  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 as method declarations  leading to flawlessly safe code  Here s an 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   quot Press a key to get a message quot        Console Read        PrintSomewhere PrintOnScreen   quot Hello world quot        The standard library s way Alternatively  you can use a delegate that s part of the  NET Standard   Action wraps up a parameterless void method  Action lt T1 gt  wraps up a void method with one parameter of type T1  Action lt T1  T2 gt  wraps up a void method with two parameters of types T1 and T2  respectively  And so forth    Func lt TR gt  wraps up a parameterless function with TR return type  Func lt T1  TR gt  wraps up a function with TR return type and with one parameter of type T1  Func lt T1  T2  TR gt  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 using predefined delegates like these  parameter names won t describe what they have to be passed in  nor is the delegate name meaningful on what it s supposed to do  Therefore  be cautious about when to use these delegates and 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 still mentioning it in my answer for the sake of completeness

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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 lt string  int gt  myMethodName                      do stuff         int i   myMethodName  My String                  do more stuff         return true             public bool Test                 return RunTheMethod Method1

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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      gt  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 lt string int gt  Method1    MyString1      Console WriteLine InvokeMethod new Func lt string  int gt  Method2    MyString2

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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

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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 lt string  int gt  delegate1  So your code can become correct with as simple a change as this   public bool RunTheMethod Func lt string  int gt  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   gt  x Length     That will create an anonymous function like this      The  lt  gt  in the name make it  unspeakable  - you can t refer to this method directly    in your own code  private static int  lt  gt  HiddenMethod  lt  gt  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 lt T  TResult gt  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

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If you want the ability to change which method is called at run time I would recommend using a delegate   http   www codeproject com KB cs delegates step1 aspx  It will allow you to create an object to store the method to call and you can pass that to your other methods when it s needed

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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

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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

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public static T Runner lt T gt  Func lt T gt  funcToRun          Do stuff before running function as normal     return funcToRun        Usage   var ReturnValue   Runner      gt  GetUser 99

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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 parameter

[c#] Pass Method as Parameter using C#

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