Question

我有以下方法：

List<DropdownMenuItem<String>> _buildGitIgnoreTemplateItems() {
    var _dropDownMenuItems = List<DropdownMenuItem<String>>();

    _gitIgnoreTemplateNames.forEach((templateName) {
        _dropDownMenuItems.add(DropdownMenuItem(
            child: Text(templateName),
            value: templateName,
        ));
    });

    return _dropDownMenuItems;
}

我想要实现的是删除变量_dropDownMenuItems，例如：

List<DropdownMenuItem<String>> _buildGitIgnoreTemplateItems() {
    _gitIgnoreTemplateNames.forEach((templateName) {
        **yield return** DropdownMenuItem(
            child: Text(templateName),
            value: templateName,
        );
    });
}

您可以在其他语言中看到类似的实现，例如：C#

Answer 1

C＃太早了，但是看起来像Synchronous generators

/**
 * You are given startingAmount of Apples. Whenever you eat a certain number of
 * apples (newEvery), you get an additional apple.
 *
 * What is the maximum number of apples you can eat?
 *
 * For example, if startingAmount equals 3 and newEvery equals 2, you can eat 5 apples in total:
 * 
 * Eat 2. Get 1. Remaining 2.
 * Eat 2. Get 1. Remaining 1.
 * Eat 1.
 */

但是也许你只是想要

Iterable<DropdownMenuItem<String>> _buildGitIgnoreTemplateItems() sync* {
    for(var templateName in _gitIgnoreTemplateNames) {
        yield DropdownMenuItem(
            child: Text(templateName),
            value: templateName,
        );
    }
}

Answer 2

dart中的等效项是Stream和StreamController用于异步。和Iterable用于同步。您可以手动创建它们，也可以使用带有async*或sync*关键字的自定义功能

Iterable<String> foo() sync* {
  yield "Hello";
}


Stream<String> foo() async* {
  yield "Hello";
}

Answer 3

Dart具有更简单的语法来实现您想要的目标：

List<DropdownMenuItem<String>> _buildGitIgnoreTemplateItems() {
  return _gitIgnoreTemplateNames
      .map((g) => DropdownMenuItem(
            child: Text(g),
            value: g,
          ))
      .toList();
}

C＃在循环上的Dart / Flutter返回列表<string>上的收益率返回

3 个答案: