android listview 每行的金额 求总和

我用listview 把一些数据通过simpleAdapter 展示出来。 详情如截图

加减 按钮是修改数量。 与此同时，右边的 和 也会随着数量的更改而 更新。

java代码 已经测试过。 目前加减和一切正常。

int cal_quantity;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main8);    List<HashMap<String, String>> aList = new ArrayList<HashMap<String, String>>();    final String name[]={"apple","orange","pear"};    final String quantity[]={"1","2","3"};    final String price[]={"5","10","2"};    for(int i=0;i<name.length;i++){        HashMap<String, String> map = new HashMap<>();        map.put("name",name[i]);        map.put("quantity",quantity[i]);        map.put("price",price[i]);        aList.add(map);    }    String[] from = {"name","quantity","price"};    int[] to = {R.id.name,R.id.quantity,R.id.price};    SimpleAdapter adapter = new SimpleAdapter(this, aList, R.layout.main7, from, to){        @Override        public View getView(final int position, View convertView, ViewGroup parent) {            View v = super.getView(position, convertView, parent);            final TextView tv_quantity=(TextView)v.findViewById(R.id.quantity);            final TextView tv_price=(TextView)v.findViewById(R.id.price);            final TextView tv_total=(TextView)v.findViewById(R.id.total);            final int get_quantity = Integer.parseInt(tv_quantity.getText().toString());            final double get_price= Double.parseDouble(tv_price.getText().toString());            final double get_total=get_quantity*get_price;            tv_total.setText(get_total+"");            Button minus=(Button)v.findViewById(R.id.minus);            minus.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View view) {                    cal_quantity=Integer.parseInt(tv_quantity.getText().toString());                    if(cal_quantity!=1){                        cal_quantity=cal_quantity-1;                    }                    tv_quantity.setText(cal_quantity+"");                    double get_total=cal_quantity*get_price;                    tv_total.setText(get_total+"");                }            });            Button plus=(Button)v.findViewById(R.id.plus);            plus.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View view) {                    cal_quantity=Integer.parseInt(tv_quantity.getText().toString());                    cal_quantity=cal_quantity+1;                    tv_quantity.setText(cal_quantity+"");                    double get_total=cal_quantity*get_price;                    tv_total.setText(get_total+"");                }            });            return v;        }    };    ListView listView = (ListView) findViewById(R.id.listview);    listView.setAdapter(adapter);}

xml - listview和底部的总和 textview分开

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/activity_main8"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context="com.yu.singleton.Main8Activity"android:orientation="vertical"><LinearLayout    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_weight="0.3"    android:layout_height="match_parent">    <ListView        android:layout_width="match_parent"        android:layout_height="match_parent"        android:id="@+id/listview" /></LinearLayout><LinearLayout    android:orientation="vertical"    android:layout_width="match_parent"    android:background="@android:color/holo_blue_dark"    android:layout_weight="0.7"    android:layout_height="match_parent">    <TextView        android:text="Total"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/textView3"        android:textAlignment="center"        android:textSize="36sp" /></LinearLayout></LinearLayout>

**那么我的问题是如何把每一排最右边的 Textview 值 加起来 ，然后再底部展示出总和？ 我知道大概是用循环，但是实际操作完全没有头绪。
请大神们指点**