You should declare your manual created button as a field, outside the constructor:
private myButtonObject start;
Something like that
public class MainForm()
{
// Declare the button as a field in order to have access to it
// in any property/method/constructor within the class
private myButtonObject start;
...
}
public MainForm()
{
InitializeComponent();
start = new myButtonObject();
EventHandler myHandler = new EventHandler(start_Click);
start.Click += myHandler;
start.Location = new System.Drawing.Point(200, 500);
start.Size = new System.Drawing.Size(101, 101);
this.Controls.Add(start);
...
}
private void setInvisible()
{
...
// You can access the button within setInvisible() method
start.Visible = false;
}