flutter - 让用户从 CupertinoPicker(onSelectedItemChanged) 中选择值，然后它应该发送调用到 API

Question

我正在使用适用于 iOS 用户的 CupertinoWidget 滚动列表并检查货币价格。但是当发生滚动时，onSelectedItemChanged 会为列表中的每个值向 API 发送回调。我阅读了文档，但无法理解该怎么做。有例子就好了。

在文档中它被称为 CupertinoPicker > onSelectedItemChanged property

This can be called during scrolls and during ballistic flings. To get the value only when the scrolling settles, use a NotificationListener, listen for ScrollEndNotification and read its FixedExtentMetrics.

 NotificationListener cupertinoPickerList() {
    List<Text> textWidgetList = [];
    for (String curreny in currenciesList) {
      textWidgetList.add(
        Text(
          curreny,
          style: TextStyle(
            color: Colors.white,
          ),
        ),
      );
    }
    return NotificationListener<ScrollNotification>(
      onNotification: (scrollNotification) {
        if (scrollNotification is ScrollEndNotification) {
          return true;
        } else {
          return false;
        }
      },
      child: CupertinoPicker(
        itemExtent: 30,
        scrollController: FixedExtentScrollController(initialItem: 19),
        onSelectedItemChanged: (selectedIndex) {
          selectedCurreny = currenciesList[selectedIndex];
          updateUI(selectedCurreny);
          print(selectedCurreny);
        },
        children: textWidgetList,
      ),
    );
  }

Answer 1

您可以检查 scrollNotification 的 metrics 是否属于 FixedExtentMetrics 类型。此类型具有值 itemIndex，您可以使用它来确定当前选择的项目。

  return NotificationListener<ScrollNotification>(
    onNotification: (scrollNotification) {
      if (scrollNotification is ScrollEndNotification &&
      scrollNotification.metrics is FixedExtentMetrics) {
        (scrollNotification.metrics as FixedExtentMetrics).itemIndex; // Index of the list
        return true;
      } else {
        return false;
      }
    },