如何在dart中映射地圖的回傳

我嘗試映射映射的回傳，但看起來第一個映射不回傳迭代的結果。我在這里有點困惑。

我試試那個代碼。它只是簡單地迭代“行”并回傳迭代的資料：

void main() {
  final Map<String, dynamic> treeData = {
    "title": "test",
    "row": [
      [
        {
          "img":
              "https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg"
        },
        {
          "img":
              "https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg"
        }
      ],
      [
        {
          "img":
              "https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg"
        }
      ]
    ],
  };

var mappedData = treeData['row'].map((data) {
    print("");
    print("!!!!!!!!!!!!!!!!!!!");
    print(data);
    return data;
  }).toList().map((data) {
    print("");
    print("-------------------");
    print(data);
    return data;
  }).toList();
  
  print("");
  print("???????????");
  print(mappedData);
}

我得到的結果不是我所期望的。如您所見，看起來 2 次迭代完全相同。

!!!!!!!!!!!!!!!!!!!
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}, {img: https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg}]

!!!!!!!!!!!!!!!!!!!
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}]

-------------------
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}, {img: https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg}]

-------------------
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}]

???????????
[[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}, {img: https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg}], [{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}]]

我希望這樣的事情，第二次迭代遍歷第二個陣列并回傳物件值。

!!!!!!!!!!!!!!!!!!!
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}, {img: https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg}]

!!!!!!!!!!!!!!!!!!!
[{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}]

-------------------
{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}
{img: https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg}

-------------------
{img: https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg}

有沒有辦法讓它以那種方式作業？什么是最好的選擇？

感謝您的回答。

uj5u.com熱心網友回復：

是的，有一種方法可以讓它像這樣作業：

void main() {
  final Map<String, dynamic> treeData = {
    "title": "test",
    "row": [
      [
        {
          "img":
              "https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg"
        },
        {
          "img":
              "https://cdn.pixabay.com/photo/2015/03/27/13/16/maine-coon-694730_960_720.jpg"
        }
      ],
      [
        {
          "img":
              "https://cdn.pixabay.com/photo/2014/11/30/14/11/cat-551554_960_720.jpg"
        }
      ]
    ],
  };

  var mappedData = treeData['row']
      .map((data) {
        print("");
        print("!!!!!!!!!!!!!!!!!!!");
        print(data);
        return data;
      })
      .toList()
      .map((data) {
        for (var item in data) {
          print("");
          print(item);
        }
        print("-------------------");

        return data;
      })
      .toList();

  print("");
  print("???????????");
  print(mappedData);
}

本質上，您希望列印傳遞給第二個函式的串列中的每個專案。您將獲得與第二次迭代相同的結果，因為您將第一次迭代的輸出轉換為函式正在接收的相同輸入。

uj5u.com熱心網友回復：

哦，我覺得已經是深夜了，問這個問題的時候我很累..我找到了我誤導性問題的解決方案..

                Row(children: [
              ...treeData['row']
                  .map((data) => Column(children: [
                        ...data.map((item) => Image.network(
                              item['img'],
                              fit: BoxFit.cover,
                              alignment: Alignment.topCenter,
                            ))
                      ]))
                  .toList()

那是如此簡單和容易..似乎有時我們需要睡覺，伙計們（我）..><

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