addRule(RelativeLayout.BELOW, id) doesn't work

Question

I try to create 5 buttons below each other, but they appear on each other

ArrayList<Button> btn = new ArrayList<>();
for (int i=0; i<10; i++) {
        Log.d("TEST", Integer.toString(i));

        btn.add(new Button(this));
        btn.get(i).setText(Integer.toString(i));
        if (i == 0) {

            btn.get(i).setLayoutParams(new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.WRAP_CONTENT));
        } else {
            RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
            lp.addRule(RelativeLayout.BELOW, btn.get(i-1).getId());
            btn.get(i).setLayoutParams(lp);
        }
        ll.addView(btn.get(i)); 

What is wrong with my code?

Answer 1

Solved by adding btn.get(i).setId(View.generateViewId()). All id of buttons was -1 before using setId().

Answer 2

From how you've named your layout, "ll", it seems you're adding those buttons to a LinearLayout. If that's the case, try changing that container layout to a RelativeLayout.