动态 布局文件 外边距

引用：http://www.devdiv.com/thread-73074-1-1.html

LinearLayout.LayoutParams para=new LinearLayout.LayoutParams(
            LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT );
        para.setMargins(20, 20, 20, 20); //left,top,right, bottom
        para.gravity = Gravity.RIGHT;
        tv.setLayoutParams(para);
        tv.setBackgroundResource(R.drawable.icon);