How can I convert List<Item> to Map<Datetime, List<Item>> in dart / Flutter

Question

I have a list of difined Todo items like:

Todo{
 Datetime datetime;
 String task;
}

List todos = [todo1, todo2,...]

And I need to convert it to a map with type Map<Datetime, List<String>> , but in todos list, I have some todo with the same Datetime so when I use code like:

todos.forEach((todo) => map2[todo.datetime] = todo.task); the next todo will be replaced if the key is the same.

So sorry if this is a silly question, I have searched on Google but nothing there. Thanks, Hung PT.

Answer 1

尝试这个

todos.forEach((todo) => map2[todo.datetime] = map2[todo.datetime] == null ? [...map2[todo.datetime], todo.task] : [todo.task]);