C# Passing a method as a parameter to another method

Question

I have a method that is called when an exception occurs:

public void ErrorDBConcurrency(DBConcurrencyException e)
{
    MessageBox.Show("You must refresh the datasource");
}

What i would like to do is pass this function a method so if the user clicks Yes then the method is called eg

public void ErrorDBConcurrency(DBConcurrencyException e, something Method)
{
    if (MessageBox.Show("You must refresh the datasource") == DialogResult.OK)
        Method();
}

The Method may or may not have parameters, if this is the case i would like to pass them too.

How can i acheive this?

Answer 1

You can use the Action delegate type.

public void ErrorDBConcurrency(DBConcurrencyException e, Action method)
{
    if (MessageBox.Show("You must refresh the datasource") == DialogResult.OK)
        method();
}

Then you can use it like this:

void MyAction()
{

}

ErrorDBConcurrency(e, MyAction); 

If you do need parameters you can use a lambda expression.

ErrorDBConcurrency(e, () => MyAction(1, 2, "Test")); 

Answer 2

Add an Action as parameter:

public void ErrorDBConcurrency(DBConcurrencyException e, Action errorAction)
{
   if (MessageBox.Show("You must refresh the datasource") == DialogResult.OK)
       errorAction()
}

and then you can call it like this

ErrorDBConcurrency(ex, () => { do_something(foo); });

or

ErrorDBConcurrency(ex, () => { do_something_else(bar, baz); });

Answer 3

You need to use a delegate as the parameter type.

If Method returns void , then something is Action , Action<T1> , Action<T1, T2> , etc (where T1...Tn are the parameter types for Method ).

If Method returns a value of type TR , then something is Func<TR> , Func<T1, TR> , Func<T1, T2, TR> , etc.

Answer 4

Look into the Func and Action classes. You can achieve this using the following:

public void ErrorDBConcurrency(DBConcurrencyException e, Action method)
{
    if (MessageBox.Show("You must refresh the datasource") == DialogResult.OK)
        method()
}

public void Method()
{
    // do stuff
}
//....

Call it using

ErrorDBConcurrency(ex, Method)

Take a look at this article for some details. If you want your method to take a parameter, use Action, Action, etc. If you want it to return a value, use Func etc. There are many overloads of these generic classes.

Answer 5

public delegate void MethodHandler(); // The type

public void ErrorDBConcurrency(DBConcurrencyException e, MethodHandler Method) // Your error function

ErrorDBConcurrency (e, new MethodHandler(myMethod)); // Passing the method