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Cannot convert from 'method group' to 'System.Action<object>' error

I have created the following function:

public void DelegatedCall(Action<Object> delegatedMethod)


And defined the following method

public void foo1(String str) { }


However, when I try to call DelegateCall with foo1:

DelegateCall

foo1

DelegatedCall(foo1);


...I get the following compiler error:

Argument 1: cannot convert from 'method group' to 'System.Action<object>'

Argument 1: cannot convert from 'method group' to 'System.Action<object>'

What is the reason for this error and how can I correct it? Unfortunately, casting foo1 to Action is not an option.

foo1

Action

3 Answers
3

DelegatedCall expects a delegate that takes any object as an argument. But your function foo1 that you are passing to DelegatedCall can only cope with a string argument. So, the conversion isn't type-safe and thus is not possible.

DelegatedCall

object

foo1

DelegatedCall

string

Input parameters are contra-variant, but your code needs covariance. (See Difference between Covariance & Contra-variance.)

You can make DelegatedCall generic:

DelegatedCall

DelegatedCall<T>(Action<T> action)


...or have it take any delegate:

DelegatedCall(Delegate action)


But then implementing it is ugly and requires reflection. It also doesn't verify that the function has only one parameter at compile-time.

Variance doesn't work that way around; you would need

DelegatedCall(obj => foo1((string)obj));


As even in 4.0 it won't believe that every object is a string.

Note that if it was foo1(object) and Action<string> (i.e. the other way around) it probably would work (in 4.0), since every string is an object.

foo1(object)

Action<string>

private void DeleteStudent(ObservableCollection<User> StudentCollection, User Instance)
{
StudentCollection.Remove(StudentCollection.SingleOrDefault(i => i.UserId == Instance.UserId));
}


Cannot convert from 'method group' to 'System.Action' error

kindly help me to how to convert method to action object???

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