飞镖：不带运行功能的返回变量

由 发布于 flutterdart
 收藏

我有一系列看起来像这样的物品：

  final List<Map<String, String>> dateIdeas = [
    {'Description': 'Drink Cocktails','Image': 'assets/images/cocktailsfull.jpg'},
    {'Description': 'Go for dinner!', 'Image': "assets/images/dinner.jpg"},
];

当用户点击按钮时，第一项将从数组中删除。

removeItem() {
    setState(() {
      dateIdeas.removeAt(index);
    });
  }

这可以正常工作。但是，我希望用户能够撤消此操作。我对此的解决方案是执行以下操作：

  1. Have the removeItem function return what the array looked like before the removal:
  Map<String, String> removeItemLiked() {
    final removed = dateIdeas[index];
    setState(() {
      _controller.reset();
      likes.add(dateIdeas[index]['Description']);
      dateIdeas.removeAt(index);
    });
    return removed;
  }
  1. Have an undo function that adds the item back into the array at index 0:
  void undo() {
    setState(() {
      Map<String, String> result = removeItemLiked();
      dateIdeas.insert(0, result);
    });
  }

The issue here is that when triggering the undo function it also retriggers removeItem. How can I have the old array stored to a variable so I can always use it later on?

评论
小萝莉m
小萝莉m

The removeItem is getting called by you within the undo function. To prevent this, separate the function call from the removed variable.

// within stateful widget, declare 'removed'...
Map<String, String> removed;

您的其他函数将像这样被修改；

  void removeItemLiked() {
    removed = dateIdeas[index];
    setState(() {
      _controller.reset();
      likes.add(dateIdeas[index]['Description']);
      dateIdeas.removeAt(index);
    });
 }

  void undo() {
    if(removed != null) {
        setState(() {
          dateIdeas.insert(0, removed);
        });
    }
 }
点赞
评论
Jim
Jim

You can store the removed item in a variable like lastRemoved and store it's index and value both. Here's a simple example:

class MyNums {
  List<int> numbers = [123, 34, 5, 436, 56, 677];
  Map<String, dynamic> lastRemoved;

  removeItem(int index) {
    lastRemoved = {
      'index': index,
      'item': numbers[index],
    };
    numbers.removeAt(index);
  }

  undoRemove() {
    if (lastRemoved != null) {
      numbers.insert(lastRemoved['index'], lastRemoved['item']);
    }
    lastRemoved = null;
  }
}

测试：

main() {
  MyNums nums = MyNums();
  print('initial:\t\t ${nums.numbers}');

  nums.removeItem(2);
  print('remove from index 2:\t ${nums.numbers}');

  nums.undoRemove();
  print('undo index 2:\t\t ${nums.numbers}');

  nums.removeItem(2);
  print('remove from index 2:\t ${nums.numbers}');

  nums.removeItem(2);
  print('remove from index 2:\t ${nums.numbers}');

  nums.undoRemove();
  print('undo index 2:\t\t ${nums.numbers}');

  nums.undoRemove();
  print('nothing to undo:\t ${nums.numbers}');
}

输出：

initial:                 [123, 34, 5, 436, 56, 677]
remove from index 2:     [123, 34, 436, 56, 677]
undo index 2:            [123, 34, 5, 436, 56, 677]
remove from index 2:     [123, 34, 436, 56, 677]
remove from index 2:     [123, 34, 56, 677]
undo index 2:            [123, 34, 436, 56, 677]
nothing to undo:         [123, 34, 436, 56, 677]
点赞
评论