We Keep Coding

Invoke Function with async method delegate in C# [duplicate]

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."));
}

C# pass methods as parameters

I'm working with an C API in C#. In C Methods are passed as parameters and I'm trying to accomplish the same thing in C#.
in C I would call the functions the following way:
LL_SetStatusCb(OnStatusRcv);
LL_SetScanCb(scanCb);
LL_Scan();
Note that the used methods are defined in the following way:
void OnStatusRcv(ll_status_t status)
void scanCb(ll_scan_result_t *result)
In C# the methods are defined in the same way but I don't know how I can pass those methods.

C# equivalent of function pointers are delegates. You can use Func and Action to pass methods as parameters. Func delegate represents method which takes N arguments and returns value, Action delegate represents void method.
Consider this
void (* myFunction)(int parameter)
in C# would be
Action<int>

Please try this code:
create ll_scan_result_t and ll_status_t classes.
class Program
{
delegate void ActionRef<T>(ref T item);
static void Main(string[] args)
{
ll_status_t _status = new ll_status_t();
LL_SetStatusCb(_status, OnStatusRcv);
ll_scan_result_t _scan = new ll_scan_result_t();
LL_SetScanCb(ref _scan);
}
static void LL_SetScanCb(ref ll_scan_result_t status, ActionRef<ll_scan_result_t> getCachedValue)
{
//... do something
}
static void LL_SetStatusCb(ll_status_t result, Action<ll_status_t> getCachedValue)
{
//... do something
}
static void OnStatusRcv(ref ll_scan_result_t sresult)
{
//... do something
}
static void scanCb(ll_status_t s)
{
//... do something
}
}

Use the Func Delegate like below
public class myClass
{
public bool TestMethod(string input)
{
return true;
}
public bool Method1(Func<string, bool> methodName)
{
return true;
}
public void newMthod()
{
Method1(TestMethod);
}
}

In C#, the equivalent to C/C++ function pointers are delegates. A delegate is a type that represents references to methods with a particular parameter list and return type. When you instantiate a delegate, you can associate its instance with any method that has a compatible signature and return type. You can call the method through the delegate instance.
Here's an example. First, declare a delegate:
public delegate void Del(string message);
Now, Del is a delegate type which can be used to call to any method that returns void and accepts an argument of type string. Now, let's create some method matching the signature and return type of Del:
public static void DelegateMethod(string message)
{
Console.WriteLine(message);
}
Now, let's create an instance of Del and associate it with DelegateMethod, like this:
Del handler = DelegateMethod;
If you want to call DelegateMethod, you can do it by:
handler("Hello World");
Notice that since Del is a type, you can do something like this:
public static void SomeMethod(Del callback, string callbackParams)
{
callback(callbackParams);
}
Which can be used as:
SomeMethod(handler, "Hello World");
With that said, there are othes ways of working with delegates. You can use Func and Action delegates. Func is a delegate that points to a method that accepts one or more arguments and returns a value, that is, it doesn't return void. Action is a delegate that points to a method which in turn accepts one or more arguments but returns no value (returns void). In other words, you should use Action when your delegate points to a method that returns void.
Here's an example of using an Action delegate:
static void Main(string[] args)
{
Action<string> action = new Action<string>(Display);
action("Hello!!!");
Console.Read(); //Prevents from closing the command line right away.
}
static void Display(string message)
{
Console.WriteLine(message);
}
Therefore, something like
void (* funcPtr)(int) = &someFuncWithAnIntArg;
(*funcPtr)(10);
Is equivalent in C# to
Action<int> funcPtr = new Action<int>(someFuncWithAnIntArg);
funcPtr(10);
And now for a Func delegate:
static void Main(string[] args)
{
Func<int, double> func = new Func<int, double>(CalculateHra);
Console.WriteLine(func(50000));
Console.Read();
}
static double CalculateHra(int basic)
{
return (double)(basic * .4);
}
The syntax for a Func delegate accepting an argument and returning a value is like this Func<TArgument, TOutput> where TArgument is the type of the argument and TOutput is the type of returned value. There are many more types of Func (browse the left tree index) and Action (also browse the left tree index) delegates.
And last, but not least, we have the Predicate delegates which is typically used to search items in a collection or a set of data. Let's define some boilerplate code to explain:
class Customer
{
public int Id { get; set; }
public string FirstName { get; set; }
}
Then, let's try it in:
static void Main(string[] args)
{
List<Customer> customers = new List<Customer>();
customers.Add(new Customer { Id = 1, FirstName = "Stack" });
customers.Add(new Customer { Id = 2, FirstName = "Overflow" });
Predicate<Customer> pred = x => x.Id == 1;
Customer customer = customers.Find(pred);
Console.WriteLine(customer.FirstName);
Console.Read();
}
The last code snippet will print "Stack". What happened is that the Predicate delegate named prep was used as a search criteria to search in the list customers. Basically, this delegate was run on every element x of the list, and when x.Id == 1 it returns true, false otherwise. The x element where the predicate returned true is returned as the result of the Find method.

Pass action delegate as parameter in C#

I have a method which accepts an Action delegate and executes the given method as shown here:
public void ExpMethod(Action inputDel)
{
inpuDel();
}
I can call above given method like this:
ExpMethod(() => {/*do something that matters*/});
Everything works fine. So far so good. Now I want to have a method which takes a generic Action delegate as an input parameter - like this:
public void ExpGenMethod(Action<string,int> inputDel)
{
// I don't know how to call the supplied delegate as it requires parameters
}
Also, I am trying to call this ExpGenMethod in this way:
ExpGenMethod(("Hi",1) => {/*do something that makes sense*/});
But it shows syntax errors. Please let me know how to use generic action delegate in this case?

The whole point of a delegate is to have a pointer to a method. Passing parameters to it while it´s being declared is therefor pointless. Instead pass the arguments for your delegate within the method that executes the delegate, in your case within ExpGenMethod:
You should do this instead:
public void ExpGenMethod(Action<string,int> inputDel)
{
inputDel("Hi", 1);
}
And call it like this:
ExpGenMethod((x, y) => {/*do something that makes sense*/});
When executing that delegate x evaluates to "Hi" and y to 1.

Typically, you'll want the heavy lifting to happen in the ExpGenMethod and in the delegate itself you'll simply be passing the parameters to the ExpGenMethod.
using System;
public class Program
{
public static void Main()
{
ExpGenMethod((options) =>
{
options.x = "Hi";
options.y = 1;
});
}
public static void ExpGenMethod(Action<Options> inputDel)
{
var options = new Options();
inputDel(options);
/* have access to x and y so do some thing useful with these values */
Console.WriteLine(options.x);
Console.WriteLine(options.y);
}
}
public class Options
{
public string x { set; get;}
public int y { set; get; }
}

(a,b) => {/*do something that matters*/} means that a and b are parameters which are going to be specified during the call. Here you are using constant so you should do something like () => { use "Hi"; use 1;} and that would get you back to your first working example.
If you want to pass parameter you cna do it this way:
public void work()
{
ExpGenMethod((a) => {/*do something that matters*/});
}
public void ExpGenMethod(Action<int> inputDel, int parameterToUse)
{
inputDel(parameterToUse);
}

As a follow on to what #HimBromBeere explained:
The keyword Action is defined as delegate:
public delegate void Action<in T1, in T2>(T1 arg1, T2 arg2);
So if the method is defined as:
public void ExpGenMethod(Action<string,int> inputDel)
{
inputDel("Hi", 1);
}
You can call ExpGenMethod with parameters x,y is using a Lambda expression, and see the results using Console.Writeline as follows:
ExpGenMethod((x, y) => { Console.WriteLine($"{x} {y}"); });

Function Delegates with Parameters c#

I'm looking for way to call Methods with Parameters using a Function Delegate.
You could use the function delegate in the place instead of calling processOperationB. but looking for any way that the below way can be achieved.
public class Client
{
public AOutput OperationA (string param1, string param2)
{
//Some Operation
}
public BOutput OperationB(string param1, string param2)
{
//Some Operation
}
}
public class Manager
{
private Client cl;
public Manager()
{
cl=new Client();
}
private void processOperationA(string param1, string param2)
{
var res = cl.OperationA(param1,param2);
//...
}
private void processOperationB(string param1, string param2)
{
var res = cl.OperationB(param1,param2);
// trying to Call using the GetData , in that case I could get rid of individual menthods for processOperationA, processOperationB
var res= GetData<BOutput>( x=> x.OperationB(param1,param2));
}
// It could have been done using Action, but it should return a value
private T GetData<T>(Func<Client,T> delegateMethod)
{
// how a Function delegate with params can be invoked
// Compiler expects the arguments to be passed here. But have already passed all params .
delegateMethod();
}
}

Your comment reads:
Compiler expects the arguments to be passed here
But that's not really true. Yes, it expects an argument, but not what you think it expects.
Your delegateMethod parameter is a Func<Client, T>, which means it requires a single argument, of type Client, and returns a value of type T. Based on the code you've shown, you should write this instead:
private T GetData<T>(Func<Client,T> delegateMethod)
{
return delegateMethod(cl);
}
It is not clear to me what broader problem you're trying to solve is. I don't see the GetData<T>() method adding anything here; the callers could just call the appropriate "Operation..." method in each case, I'd think (i.e. as in your processOperationA() method).
But at least we can solve the compiler error. If you'd like help with that broader problem, you can post a new question. Make sure to include a good Minimal, Verifiable, and Complete code example that shows clearly what you're trying to do, and explain precisely what you've tried and what's not working.

C# methods with variable paramterlist as parameter

Hi I'm currently trying to pass methods (with no return value) as parameters to another method (so that they can be called from within the methods).
The problem I'm currently having is, that I'm using Action in the parameterlist and thus need to exactly define which parameters this method takes.
The question thus is: Is there any way to omit this? Thus that I don't have to define which parameters exactly the method has in the parameterdeclaration?
Codeexample:
public void A(int myint)
{
Console.WriteLine(myint.ToString());
}
public void B(int myint1, int myint2)
{
Console.WriteLine((myint1 + myint2).ToString());
}
public void myQuestionMethod(Action<int> parameterMethod)
{
//....Dosomething special by creating the parameters within and calling the given methods
}
myQuestionMethod(A);
myQuestionMethod(B);
Thus Aciton parameterMethod can that be replaced by something else that allows me to give methods as parameters who have differing parameters?
Edit:
I forgot to mention that the TYPE of the parameters is also not fixated.
Thus a function C could exist with (int param1, String param2)

No. There is no way to do this with the Action delegate (that's why there are 16 overloads).
You could opt, if the variables are all of the same type and have the same meaning, to create an array of integers:
public void A(params int[] myint)
{
}
public void myQuestionMethod(Action<int[]> parameterMethod)
{
//....Dosomething special by creating the parameters within and calling the given methods
}

Depending on how big your methods are, you could go for just Action and use anonymous methods rather than explicitly defining the functions
public void myQuestionMethod(Action parameterMethod)
{
//
}
...
myQuestionMethod(() => Console.WriteLine(myInt.ToString()));
myQuestionMethod(() => Console.WriteLine((myInt1 + myInt2).ToString()));

One solution would be to use reflection. Of course don't use it unless you do not have any other choice (specifying a method using its name should be avoided if possible):
public class Foo
{
public void A(int myint)
{
Console.WriteLine(myint.ToString());
}
public void B(int myint1, int myint2)
{
Console.WriteLine((myint1 + myint2).ToString());
}
public void myQuestionMethod(string parameterMethodName, params object[] parameters)
{
var method = this.GetType().GetMethod(parameterMethodName, BindingFlags.Instance | BindingFlags.Public);
method.Invoke(this, parameters);
}
}
public class Test
{
public static void Main()
{
var foo = new Foo();
foo.myQuestionMethod("B", 1, 2);
Console.Read();
}
}