在Flutter列表中添加和移除数值。

huangapple
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英文:

adding and removing values in a flutter lists

问题

下面是您要翻译的代码部分：

  1. class cartMock extends StatefulWidget {
  2.   const cartMock({Key? key}) : super(key: key);
  4.   @override
  5.   State<cartMock> createState() => _cartMockState();
  6. }
  8. class _cartMockState extends State<cartMock> {
  9.   String? _selectedFruit;
  10.   final List<String> _fruits = [];
  12.   void _addItemToList(String item) {
  13.     if (_fruits.contains(item)) {
  14.       // if the item already exists in the list, remove it
  15.       _fruits.remove(item);
  16.     }
  17.     // add the new item to the list
  18.     _fruits.add(item);
  19.   }
  21.   @override
  22.   Widget build(BuildContext context) {
  23.     return Scaffold(
  24.       body: Column(
  25.         children: [
  26.           Expanded(
  27.             child: ListView.builder(
  28.               itemCount: _fruits.length,
  29.               itemBuilder: (context, index) {
  30.                 return ListTile(
  31.                   title: Text(_fruits[index]),
  32.                 );
  33.               },
  34.             ),
  35.           ),
  36.           RadioListTile(
  37.             value: "apple",
  38.             groupValue: _selectedFruit,
  39.             onChanged: (value) {
  40.               setState(() {
  41.                 if (value != _selectedFruit) {
  42.                   _selectedFruit = value as String?;
  43.                   _addItemToList("apple");
  44.                 }
  45.               });
  46.             },
  47.             title: const Text("Apple"),
  48.           ),
  49.           RadioListTile(
  50.             value: "orange",
  51.             groupValue: _selectedFruit,
  52.             onChanged: (value) {
  53.               setState(() {
  54.                 if (value != _selectedFruit) {
  55.                   _selectedFruit = value as String?;
  56.                   _addItemToList("orange");
  57.                 }
  58.               });
  59.             },
  60.             title: const Text("Orange"),
  61.           ),
  62.         ],
  63.       ),
  64.     );
  65.   }
  66. }

希望这对您有所帮助。如果您有任何其他问题，请随时提出。

英文:

so below i have a list where for every time I tap a specific radio button value of the button gets added into an empty list , so what i'm trying to do i only want one value to only ever be contained in the list , meaning if i tap a radio button and the the value is placed in the list , the next radio button i tap must push out the former radios value and newly tapped radio button's value must be the only one in the list . my code above displays both values when i tap both radios , how can i fix this ?

  1. class cartMock extends StatefulWidget {
  2.   const cartMock({Key? key}) : super(key: key);
  4.   @override
  5.   State&lt;cartMock&gt; createState() =&gt; _cartMockState();
  6. }
  8. class _cartMockState extends State&lt;cartMock&gt; {
  9.   String? _selectedFruit;
  10.   final List&lt;String&gt; _fruits = [];
  12.   void _addItemToList(String item) {
  13.     if (_fruits.contains(item)) {
  14.       // if the item already exists in the list, remove it
  15.       _fruits.remove(item);
  16.     }
  17.     // add the new item to the list
  18.     _fruits.add(item);
  19.   }
  21.   @override
  22.   Widget build(BuildContext context) {
  23.     return Scaffold(
  24.       body: Column(
  25.         children: [
  26.           Expanded(
  27.             child: ListView.builder(
  28.               itemCount: _fruits.length,
  29.               itemBuilder: (context, index) {
  30.                 return ListTile(
  31.                   title: Text(_fruits[index]),
  32.                 );
  33.               },
  34.             ),
  35.           ),
  36.           RadioListTile(
  37.             value: &quot;apple&quot;,
  38.             groupValue: _selectedFruit,
  39.             onChanged: (value) {
  40.               setState(() {
  41.                 if (value != _selectedFruit) {
  42.                   _selectedFruit = value as String?;
  43.                   _addItemToList(&quot;apple&quot;);
  44.                 }
  45.               });
  46.             },
  47.             title: const Text(&quot;Apple&quot;),
  48.           ),
  49.           RadioListTile(
  50.             value: &quot;orange&quot;,
  51.             groupValue: _selectedFruit,
  52.             onChanged: (value) {
  53.               setState(() {
  54.                 if (value != _selectedFruit) {
  55.                   _selectedFruit = value as String?;
  56.                   _addItemToList(&quot;orange&quot;);
  57.                 }
  58.               });
  59.             },
  60.             title: const Text(&quot;Orange&quot;),
  61.           ),
  62.         ],
  63.       ),
  64.     );
  65.   }
  66. }

答案1

得分: 0

只需像这样终止_addItemToList方法：

  1. void _addItemToList(String item) {
  2.     if (_fruits.contains(item)) {
  3.         // 如果项目已经存在于列表中，请将其移除
  4.         _fruits.remove(item);
  5.         return;  // <----------------- 在这里添加 return
  6.     }
  7.     // 将新项目添加到列表中
  8.     _fruits.add(item);
  9. }
英文:

You just need to terminate _addItemToList methode like this

  1. void _addItemToList(String item) {
  2.     if (_fruits.contains(item)) {
  3.       // if the item already exists in the list, remove it
  4.       _fruits.remove(item);
  5.        return;  &lt;----------------- add return here
  6.     }
  7.     // add the new item to the list
  8.     _fruits.add(item);
  9.   }

huangapple
  • 本文由 发表于 2023年2月27日 15:57:32
  • 转载请务必保留本文链接：https://go.coder-hub.com/75577973.html
  • dart
  • flutter
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