Margin Property of an ImageView in code

Hey,
How can i set the layout_margin property of an ImageButton in code?

Heres what i've got:

Code (Text):

1.     ImageButton ib = (ImageButton) findViewById(R.id.btn_learn);
2.     MarginLayoutParams mlp = new MarginLayoutParams(ib.getLayoutParams());
3.    
4.     if(newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE)
5.         mlp.setMargins(0, 20, 0, 0);
6.     else
7.         mlp.setMargins(0, 100, 0, 0);
8.    
9.     ib.setLayoutParams(mlp); // ERROR HERE

Well, theres an error - classcastException - sure..
The setLayoutParams wants an "LayoutParams" and im giving a "MarginLayoutParams".
Well that was finally what I tried.

Any ideas how i can make that working?