Foreach与lambda的ToList().Foreach区别

1.ToList().Foreach无法保证内部异步方法的顺序；

2.Foreach 可以保证内部异步方法的顺序；

public static async Task Main()
{
    var strings = new List<string> { "B", "C", "D" };
    Console.WriteLine("A");
    strings.ForEach(async s => { await AsyncMethod(s); } );
    Console.WriteLine("E");
}

private static async Task AsyncMethod(string s)
{
    await Task.Run(() => { Console.WriteLine(s); });
}

strings.ForEach(async s => { await AsyncMethod(s); });

foreach (var s in strings) await AsyncMethod(s);

ForEach does not support an async delegate since it takes an Action<T>. That reduces your method to un-awaitable async void. ForEach was never intended for a Func<Task> or any other async variant. Calling .Wait on AsyncMethod will cause a deadlock with a single threaded synchronization context. You have a few choices though:

 

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