Pass method name as string and assign to delegate

Question

I seem to be going no-where fast with passing a method name as a string and assigning it to a delegate.

I want to have a class that assigns a dynamic method from a parameter but can't work out how to do it.

    private delegate void ProgressMsg(string msg);
    private ProgressMsg AddMsg;

    public Progress(string FormName, string AddMsgMethodName, bool close, bool hide)
    {
        // set properties
        this.Hide = hide;
        this.Close = close;

        // Open form if not open
        this.Frm = Application.OpenForms[FormName];
        if (this.Frm == null)
        {
            // instatiate form
            this.Frm = (Form)Assembly.GetExecutingAssembly().CreateInstance(Assembly.GetExecutingAssembly().GetName().Name + "." + FormName);

            // show form
            this.Frm.Show();
        }

        // assign delegate
        this.AddMsg = new ProgressMsg(AddMsgMethodName);

        // Hide form
        this.Frm.Visible = !Hide;


    }

How can I pass the name of a form, and the method to call and then assign to the delegate the method from the form?

Robert S. · Accepted Answer · 2015-03-04 14:22:00Z

4

this.AddMsg = (ProgressMsg)Delegate.CreateDelegate(typeof(ProgressMsg), this.Frm, AddMsgMethodName);

answered Mar 4, 2015 at 14:22

Robert S.

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1 Comment

user2024839 Over a year ago

Great thanks. Always like it when the code can be reduced like that :-) That first line was a little difficult to read for me anyhow!

user2023861 · Accepted Answer · 2015-03-04 14:21:26Z

In .Net 4.5 you can use the CallerMemberNameAttribute to get the name of the calling method. I use this all the time with INotifyPropertyChanged. This way I can write this:

private string _name;
public string Name
{
    get { return this._name; }
    set
    {
        if (this._name != value)
        {
            this._name = value;
            this.OnPropertyChanged(); //no argument passed
        }
    }
}

public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberNameAttribute]string propertyName = "")
{ //propertyName will be set to "Name"
    if (this.PropertyChanged != null)
        this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

See here for more

Heinzi · Accepted Answer · 2015-03-04 14:15:38Z

1

You can use reflection. The following code assumes that the method in question always takes exactly one parameter of type string.

var method = this.Frm.GetType().GetMethod(AddMsgMethodName,
      new Type[] { typeof(string) });

this.AddMsg = (ProgressMsg)Delegate.CreateDelegate(typeof(ProgressMsg), this.Frm, method);

answered Mar 4, 2015 at 14:15

Heinzi

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5 Comments

user2024839 Over a year ago

I'm getting a casting (or lack of) error? Cannot implicitly convert type 'System.Delegate' to 'Progress.ProgressMsg'. An explicit conversion exists (are you missing a cast?)

user2024839 Over a year ago

I explicitly cast it and it seems to be OK. this.AddMsg = (ProgressMsg) Delegate.CreateDelegate(typeof(ProgressMsg), method);

user2024839 Over a year ago

Thanks, that was doing my head in. I'm very fuzzy when it comes to delegates, If I have to hard code the method to call, why am I not simply calling it? - I'm missing some point for sure, and just hope it comes with time.

Robert S. Over a year ago

You don't need the first line as you can simply provide the method name instead of the MethodInfo as a parameter for CreateDelegate. See my answer. You won't have to specify parameter types for the delegate as well then.

Heinzi Over a year ago

@RobertS.: Nice catch, +1 from me. I'll leave my answer here, since it's more robust with respect to multiple overloads.

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