Question

i get an InvalidArgumentException while casting Control to System.Windows.Forms.Textbox:

Unable to cast object of type ‘System.Windows.Forms.Control’ to type ‘System.Windows.Forms.TextBox’.

System.Windows.Forms.Control control = new System.Windows.Forms.Control();
control.Width = currentField.Width;

//here comes the error
((System.Windows.Forms.TextBox)control).Text = currentField.Name;

I am doing this, because I have different Controls (Textbox, MaskedTextbox, Datetimepicker…), which will dynamically be added to a panel and have the same basic properties (Size, Location… -> Control)

Why isn’t the cast possible?

Answer 1

The cast fails because control is not a TextBox. You can treat a TextBox as a control (higher up the type hierarchy) but not any Control as a TextBox. For setting common properties you can just treat everything as Control and set them whereas you have to create the actual controls you want to use beforehand:

TextBox tb = new TextBox();
tb.Text = currentField.Name;

Control c = (Control)tb; // this works because every TextBox is also a Control
                         // but not every Control is a TextBox, especially not
                         // if you *explicitly* make it *not* a TextBox
c.Width = currentField.Width;