Textview中部分文字改变大小颜色的方法

TextView tv=(TextView)findViewById(R.id.tv);
TextView tv2=(TextView)findViewById(R.id.tv2);
TextView tv3=(TextView)findViewById(R.id.tv3);
String str="前面正常<font color='#ff0000'>我是被更改的部分</font>";
tv.setTextSize(20);
tv.setText(Html.fromHtml(str));
String str2="前面正常<font color='#ff0000'><small>我是小1号的</small></font>";
tv2.setTextSize(20);
tv2.setText(Html.fromHtml(str2));
String str3="前面正常<font color='#ff0000'><small><small><small>我是小3号的</small></small></small></font>";
tv3.setTextSize(20);
tv3.setText(Html.fromHtml(str3));