将新项目添加到列表中替换列表颤振中的旧项目答案

【问题标题】：Adding new Items to List replacing old Items in List Flutter将新项目添加到列表中替换列表颤振中的旧项目
【发布时间】：2020-05-25 20:31:45
【问题描述】：

当我将新项目添加到我的列表时，它将覆盖之前的值。我想追加列表，但没有发生

Container(
  // color: Colors.red,
  child: Row(
    mainAxisAlignment: MainAxisAlignment.end,
    children: <Widget>[
      Container(
        width: 50,
        height: 50,
        // color: Colors.blue,
        child: FlatButton(onPressed: (){
          if(_itemCount > 0){
            setState(() {
              _itemCount--;
            });

          }
        }, child: Image(image: AssetImage("images/minus.png"),width: 20,height: 20,),),
      ),
      Container(
        child: Text("$_itemCount"),
      ),
      Container(
        width: 50,
        height: 50,
        //  color: Colors.green,
        child: FlatButton(onPressed: () async{
          setState(() {
            _itemCount++;
          });
          
          cartItemList = [{"index":widget.intex,"itemObj":widget.items,"quantity":_itemCount}];
          print(addedItems(cartItemList));
          
          final prefs = await SharedPreferences.getInstance();
          await prefs.setStringList('itemList', addedItems(cartItemList));
        }, child: Image(image: AssetImage("images/plus.png"),width: 20,height: 20,),),
      ),
    ],
  ),
),

我有一个ListView，ListView 项目将从 API 获取，当我单击一个项目时，我希望它添加到列表中，我可以将其保存在 sharedpreference 中。但是每次我点击之前的按钮时，都会被新的按钮覆盖。

以下是将数据转换为 JSON 格式的代码

List<String> addedItems(List<dynamic> cartList){
  try {
    var res = cartList.map((v) => json.encode(v)).toList();
    return res;
  } catch (err) {
    // Just in case
    return [];
  }
},

输出是

当我添加第一项时

 [{"itemObj":{"item_price":22.0,"item_name":"DINE SPECIAL BREAKFAST","item_img":" ","item_code":"001","item_discount":0.0,"item_id":552,"category_id":12},"quantity":1}]

当我再次添加相同的项目时

 [{"itemObj":{"item_price":22.0,"item_name":"DINE SPECIAL BREAKFAST","item_img":" ","item_code":"001","item_discount":0.0,"item_id":552,"category_id":12},"quantity":2}]

（数量增加）

当我添加一个新项目时

 [{"itemObj":{"item_price":20.0,"item_name":"English Breakfast","item_img":" ","item_code":"002","item_discount":0.0,"item_id":71,"category_id":12},"quantity":1}]

（DINE SPECIALs 在哪里？）

但我想要像这样的输出

[{"itemObj":{"item_price":22.0,"item_name":"DINE SPECIAL BREAKFAST","item_img":" ","item_code":"001","item_discount":0.0,"item_id":552,"category_id":12},"quantity":2},{"item_price":20.0,"item_name":"English Breakfast","item_img":" ","item_code":"002","item_discount":0.0,"item_id":71,"category_id":12},"quantity":1}]

【问题讨论】：

标签： flutter dart

【解决方案1】：

每次点击按钮时都会设置列表

cartItemList = [{"index":widget.intex,"itemObj":widget.items,"quantity":_itemCount}];

也许你需要做的是

cartItemList.add({"index":widget.intex,"itemObj":widget.items,"quantity":_itemCount});

【讨论】：