解决的办法
PopupWindow pw = new PopupWindow(ppLayout,900,800);
//设置透明背景,不然也没效果
pw.setBackgroundDrawable(new BitmapDrawable());
//设置焦点,不然无法弹出输入法
pw.setFocusable(true);
//以下两句不能就颠>
pw.setSoftInputMode(PopupWindow.INPUT_METHOD_NEEDED);
pw.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_RESIZE);
pw.showAtLocation(tv, Gravity.BOTTOM, 0, 0);