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."));
}
Related
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.
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();
}
}
I have a list of methods that do pretty much the same thing, except a few differences:
void DoWork(string parameter1, string parameter2)
{
//Common code
...
//Custom code
...
//Common code
...
}
I want to streamline the solution with reusing the common code by passing custom code from another method.
I assume I have to use an action with parameters to accomplish this, but can't figure out how.
You could try the Template method pattern
Which basically states soemthing like this
abstract class Parent
{
public virtual void DoWork(...common arguments...)
{
// ...common flow
this.CustomWork();
// ...more common flow
}
// the Customwork method must be overridden
protected abstract void CustomWork();
}
In a child class
class Child : Parent
{
protected override void CustomWork()
{
// do you specialized work
}
}
The other answers are great, but you may need to return something from the custom code, so you would need to use Func instead.
void Something(int p1, int p2, Func<string, int> fn)
{
var num = p1 + p2 + fn("whatever");
// . . .
}
Call it like this:
Something(1,2, x => { ...; return 1; });
Or:
int MyFunc(string x)
{
return 1;
}
Something(1,2 MyFunc);
You would use delegates to handle this. It would likely look something like:
void DoWork(string parameter1, string parameter2, Action<string,string> customCode)
{
// ... Common code
customCode(parameter1, parameter2);
// ... Common code
customCode(parameter1, parameter2);
// ... Common code
}
If the custom code doesn't have to interact with the common code, it's easy:
void DoWork(..., Action custom)
{
... Common Code ...
custom();
... Common Code ...
}
Assuming you need to use the two string parameters in the custom code, the following should get the job done. If you don't actually care about the results of the custom code, you can replace Func<string, string, TResult> with Action<string, string>. Additionally, if your custom code needs to process results from the common code above it, you can adjust the parameter types that your Func<> (or Action<>) takes in and then pass in the appropriate values.
void DoWork(string parameter1, string parameter2, Func<string, string, TResult> customCode) {
//Common code
var customResult = customCode(parameter1, parameter2);
//Common code
}
Using Func<T, TResult>: http://msdn.microsoft.com/en-us/library/bb534960
Using Action<T>: http://msdn.microsoft.com/en-us/library/018hxwa8
I have the following code:
public static MyMethod()
{
...Do something
ProtectedMethod(param1, param2);
...Do something
}
protected static void ProtectedMethod(IEnumerable<string> param1, string param2, int param3 = 1)
{
... Do something
}
Take notice of the optional param3 parameter.
Now for quite a few reasons I need to extract the code of the MyMethod method into its own class but I cannot extract ProtectedMethod with it because of all the classes that are inheriting from this one and I need to keep the changes small and isolated. So I figured I could have an Action<> delegate in the new class with the same signature as ProtectedMethod.
The problem is that if I declare the delegate like this:
protected readonly Action<IEnumerable<string>, string, int> m_ProtectedMethod;
The extracted code does not like it because it says the method is only being invoked with two parameters.
And if I declare the delegate like so:
protected readonly Action<IEnumerable<string>, string> m_ProtectedMethod;
When I send it as a parameter to the new class it does not like it either because the method is defined as having three parameters not two.
So far the only way I have thought of to solve this is to create an overloaded version of ProtectedMethod to eliminate the optional parameter.
Is this the only option or is there another way of doing it since now the preferred choice is to have optional parameters instead of overloaded methods?
Optional parameters are an attribute of a method or delegate parameter. When you call a signature (method or delegate) that has a known optional parameter at compile-time, the compiler will insert the optional parameter value at the callsite.
The runtime is not aware of optional parameters, so you can't make a delegate that inserts an optional parameter when it's called.
Instead, you need to declare a custom delegate type with an optional parameter:
public delegate void MyDelegate(IEnumerable<string> param1, string param2, int param3 = 1);
When calling this delegate, you will be able to omit the third parameter, regardless of the declaration of the method(s) it contains.
It would depend on how m_ProtectedMethod would be consumed, but I found a compromise in my own situation, where I use one overload more than the other.
Simply define a simpler (having less generic parameters) Action<> variable, which calls the more complex supplied Action variable method. This can be accomplished either in (i) local scope on use; or (ii) object scope upon assignment of Action property or object construction.
Because there is no such thing as variable/property overloading, you need two different names, for the resulting two related Action variables.
EG i: Local Scope (probably not the most suitable for your scenario)
public MyMethod(Action<IEnumerable<string>, string, int> m_ProtectedMethod2)
{
Action<IEnumerable<string>, string> m_ProtectedMethod = (p1,p2) => {
m_ProtectedMethod2(p1,p2,1); //The value 1 is the default 3rd parameter
}
...Do something
m_ProtectedMethod(param1, param2);
...Do something
...If something
m_ProtectedMethod2(param1, param2, param3); //Calling the more complex form directly
...Do something
}
EG ii: Object Scope
private Action<IEnumerable<string>, string, int> m_ProtectedMethod2 = null;
private Action<IEnumerable<string>, string> m_ProtectedMethod = null;
protected Action<IEnumerable<string>, string, int> ProtectedMethod
{
get { return m_ProtectedMethod2; }
set {
m_ProtectedMethod2 = value;
m_ProtectedMethod = (p1,p2) => {
m_ProtectedMethod2(p1,p2,1); //The value 1 is the default 3rd parameter
}
}
}
public MyMethod()
{
...Do something
m_ProtectedMethod(param1, param2);
...Do something
...If something
m_ProtectedMethod2(param1, param2, param3); //Calling the more complex form directly
...Do something
}
Note in both cases I designed the default setting value to be the more awkwardly named variable, having the 2 suffix, such that upon consumption the simpler overload has the more basic variable name.
Hoping to help others with what I find as being a more elegant implementation of overloading mixed with the (delegate-oriented) strategy pattern.
public class OverloadExample {
private Action<int, bool> _implementation;
public OverloadExample() {
_implementation = defaultImplementation;
}
public OverloadExample(Action<int, bool> implementation) {
_implementation = implementation;
}
protected void defaultImplementation(int aInt, bool aBool) {
//
}
public void Implementation(int someInt, bool someBool = true) {
_implementation(someInt, someBool);
}
}
Usage:
new OverloadExample().Implementation(9001);
new OverloadExample().Implementation(9001, false);
I want to have a library that will have a function in it that accepts an object for it's parameter.
With this object I want to be able to call a specified function when X is finished. The function that will be called is to be specified by the caller, and X will be done and monitored by the library.
How can I do this?
For reference I'm using C# and .NET 3.5
Two options for you:
Have the function accept a delegate (Action for a callback that doesn't return anything, Func for one that does) and use an anonymous delegate or Lambda Expression when calling it.
Use an interface
Using a delegate/lambda
public static void DoWork(Action processAction)
{
// do work
if (processAction != null)
processAction();
}
public static void Main()
{
// using anonymous delegate
DoWork(delegate() { Console.WriteLine("Completed"); });
// using Lambda
DoWork(() => Console.WriteLine("Completed"));
}
If your callback needs to have something passed to it, you can use a type parameter on Action:
public static void DoWork(Action<string> processAction)
{
// do work
if (processAction != null)
processAction("this is the string");
}
public static void Main()
{
// using anonymous delegate
DoWork(delegate(string str) { Console.WriteLine(str); });
// using Lambda
DoWork((str) => Console.WriteLine(str));
}
If it needs multiple arguments, you can add more type parameters to Action. If you need a return type, as mentioned use Func and make the return type the last type parameter (Func<string, int> is a function accepting a string and returning an int.)
More about delegates here.
Using an interface
public interface IObjectWithX
{
void X();
}
public class MyObjectWithX : IObjectWithX
{
public void X()
{
// do something
}
}
public class ActionClass
{
public static void DoWork(IObjectWithX handlerObject)
{
// do work
handlerObject.X();
}
}
public static void Main()
{
var obj = new MyObjectWithX()
ActionClass.DoWork(obj);
}
Sounds like a perfect recipe for delegates - in particular, callbacks with delegates are exactly how this is handled in the asynchronous pattern in .NET.
The caller would usually pass you some state and a delegate, and you store both of them in whatever context you've got, then call the delegate passing it the state and whatever result you might have.
You could either make the state just object or potentially use a generic delegate and take state of the appropriate type, e.g.
public delegate void Callback<T>(T state, OperationResult result)
Then:
public void DoSomeOperation(int otherParameterForWhateverReason,
Callback<T> callback, T state)
As you're using .NET 3.5 you might want to use the existing Func<...> and Action<...>
delegate types, but you may find it makes it clearer to declare your own. (The name may make it clearer what you're using it for.)
The object in question will need to implement an interface provided by you. Take the interface as a parameter, and then you can call any method that the interface exposes. Otherwise you have no way of knowing what the object is capable of. That, or you could take a delegate as a parameter and call that.
Is there a reason not to have your library provide a public event to be fired when the operation is complete? Then the caller could just register to handle the event and you don't have to worry about passing around objects or delegates.
The object implementing an interface you have provided would work, but it seems to be more the Java approach than the .NET approach. Events seem a bit cleaner to me.
You can use System.Action available in C#.NET for callback functions. Please check this sample example:
//Say you are calling some FUNC1 that has the tight while loop and you need to
//get updates on what percentage the updates have been done.
private void ExecuteUpdates()
{
Func1(Info => { lblUpdInfo.Text = Info; });
}
//Now Func1 would keep calling back the Action specified in the argument
//This System.Action can be returned for any type by passing the Type as the template.
//This example is returning string.
private void Func1(System.Action<string> UpdateInfo)
{
int nCount = 0;
while (nCount < 100)
{
nCount++;
if (UpdateInfo != null) UpdateInfo("Counter: " + nCount.ToString());
//System.Threading.Thread.Sleep(1000);
}
}