C＃飞镖/颤振返回列表的收益率列表 <String> 循环中

Question

I have the following method:

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

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

    return _dropDownMenuItems;
}

What i am trying to achived is remove the variable _dropDownMenuItems something like:

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

You can see similar implementation in other languages like: C#

Answer 1

C# is way too long ago, but it looks like Synchronous generators

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

but perhaps you just want

_gitIgnoreTemplateNames.map((templateName) => 
    DropdownMenuItem(
      child Text(templateName), 
      value: templateName)
    ).toList()

Answer 2

The equivalent in dart is with Stream and StreamController for async. And Iterable for sync. You can create them manually or using custom function with async* or sync* keywords

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


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

Answer 3

Dart has a simpler syntax to achieve what you want:

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