I know, I am answering an old question, it might be helpful for someone else, for striking out a particular portion of TextView programmatically.
TextView textView = (TextView) findViewById(R.id.textView);
textView.setText("Text need to be set here", TextView.BufferType.SPANNABLE);
Spannable spannable = (Spannable) textView.getText();
spannable.setSpan(new StrikethroughSpan(), 5, 8, Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
So, in this example code, 5 is starting position and 8 is ending position of text need to be stricken out, so after running this code we can get the text "need" with striked out. Hope it will helpful for someone else.