Android中TextView中的文字设置为不同颜色

questionDesTextView=(TextView)findViewById(R.id.question_des);
        SpannableStringBuilder builder = new SpannableStringBuilder(questionDesTextView.getText().toString());
        //ForegroundColorSpan 为文字前景色，BackgroundColorSpan为文字背景色
        ForegroundColorSpan blackSpan = new ForegroundColorSpan(Color.BLACK);
        ForegroundColorSpan graySpan=new ForegroundColorSpan(Color.GRAY);

        //第二个参数是开始的下标，第三个参数是结束的下标
        builder.setSpan(blackSpan, 0,4, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        builder.setSpan(graySpan,4,9, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        questionDesTextView.setText(builder);