C # using an asynchronous delegate to update a form on another thread cannot omit optional arguments

Update Label1 with button1:

        Private Delegate voidUpdateforminvoke (stringAstringb ="B"); Private voidUpdateForm (stringAstringb ="B") {Label1. Text= A +" - "+b; }        Private voidButton1_Click (Objectsender, EventArgs e) {Thread th=NewThread (Test); Th.        Start (); }        voidTest () {Updateforminvoke Uli=NewUpdateforminvoke (UpdateForm);  This. BeginInvoke (Uli,New Object[] {"A" }); }

Parameter count mismatch exception:

Modify Code 1:

        Private Delegate void Updateforminvoke (stringstring"B");         Private void UpdateForm (stringstring  b)        {            "" + b;        }

Modify Code 2:

        Private Delegate void Updateforminvoke (stringstring  b);         Private void UpdateForm (stringstring"B")        {             "  " + B;        }

The same error occurred as a result

Modify Code 3:

        void Test ()        {            new  Updateforminvoke (updateform);              This New Object " A " " B "  });        }

No optional arguments are omitted, no exception.

C # using an asynchronous delegate to update a form on another thread cannot omit optional arguments