Threadsafe Generic Extension method usage syntax problem

Question

Here's my extension method for invoke on a control:

 public static void Invoke<T>(this T c, Action<System.Windows.Forms.Control> DoWhat)
  where T:System.Windows.Forms.Control
 {
  if (c.InvokeRequired)
   c.Invoke(o=> DoWhat(c) );
  else
   DoWhat(c);
 }

ds is a strongly typed dataset. This works:

Action<DataGridView> a = row => row.DataSource = ds.bLog;

  this.dataGridView1.Invoke(a);

this doesn't compile:

this.dataGridView1.Invoke<DataGridView>(o => o.DataSource = ds.bLog);

and says System.Windows.Forms.Control does not contain a definition for 'DataSource'...

do I really have to break this into 2 lines? For clarity/safety should I call the generic extension method InvokeSafe?

Edit:Extension method revised (works, but I'd like to remove the named delegate requirement):

private delegate void myDel();

public static void InvokeSafe<T>(this T c, Action<T> DoWhat)
where T : System.Windows.Forms.Control
 {

  myDel d = delegate() { DoWhat(c); };
  if (c.InvokeRequired)
   c.Invoke(d);
  else
   DoWhat(c);



 }

I can't seem to figure out how to make factor out myDel into an anonymous delegate in the block?

Answer 1

The problem is that your action is only declared (in the method) to act on Control. Change it to this:

public static void Invoke<T>(this T c, Action<T> DoWhat)
    where T:System.Windows.Forms.Control
{
    if (c.InvokeRequired)
        c.Invoke((EventHandler) delegate { DoWhat(c) } );
    else
        DoWhat(c);
}

That way the compiler will infer that you want an Action<DataGridView> so the lambda expression in the caller will be able to use DataSource.

Answer 2

Try changing your method signature to:

public static void Invoke<T>(this T c, Action<T> DoWhat)

This will let your Action use the desired type that you specify.

Answer 3

To further what Jon Said, The datasource does not live on System.Windows.Forms.Control. The datasource is on the datagrid. So if you look at the error message, you will see that it is trying to set the datasource on a type that does not have a data source. Doing what Jon suggested should fix the problem.

Answer 4

Works!

public static void InvokeSafe<T>(this T c, Action<T> DoWhat)
where T : System.Windows.Forms.Control
 {

  Action d = delegate() { DoWhat(c); };
  if (c.InvokeRequired)
   c.Invoke(d);
  else
   DoWhat(c);

 }

This code does result in an InvalidOperationException- Cross-thread operation not valid:

List<customer> c=new List<customer>{new customer{ Name="test"},new customer{Name= "John doe"}};
  Thread t = new Thread(o => this.dataGridView1.DataSource = c);
  t.Start();

the new extension method does not!

List<customer> c=new List<customer>{new customer{ Name="test"},new customer{Name=   "John doe"}};
  Thread t = new Thread(o => this.dataGridView1.InvokeSafe(p => p.DataSource = c));
  t.Start();