c# - 任务的 OnCompleted 回调在哪里？

Question

我希望能够做到这一点:

class MyClass
{
    IRepo repo;
    public MyClass(IMyRepo repo) { this.repo = repo; }

    long ID { get; set; }
    string Prop1 { get; set; }
    string Prop2 { get; set; }

    public async Task LoadAsync()
    {
        await Task.WhenAll(
            repo.GetProp1ByIDAsync(ID).OnComplete(x => Prop1 = x),
            repo.GetProp2ByIDAsync(ID).OnComplete(x => Prop2 = x)
        );
    }
}

当然，我似乎找不到任何标准库具有 Task 的 OnComplete 扩展。我真的需要创建自己的方法吗？或者是否有一个库已经有了这种扩展方法？我看到有 ContinueWith 但这并没有给我展开的结果，我仍然必须 await 或 .Result 它......所以那不会阻塞线程吗？暂停第二次 repo 调用直到完成？如果它不能阻止它，那为什么我得到的结果仍然是包装的，将未包装的结果返回给我会更干净吗？还是我遗漏了什么？

Answer 1

I can't seem to find any standard library that has this OnComplete extension for Task. Do I really need to create my own or is there a library that already has this extension method? I see that there's ContinueWith but that does not give me the unwrapped result, I still have to await it or .Result it... so wouldn't that block the thread?

ContinueWith 是您正在寻找的方法； Result 不会阻塞任务，因为它在回调被调用时已经完成。

但是，ContinueWith 是一个危险的低级 API。您应该改用 await:

public async Task LoadAsync()
{
    await Task.WhenAll(
        LoadProp1Async(),
        LoadProp2Async()
    );
}

private async Task LoadProp1Async()
{
  Prop1 = await repo.GetProp1ByIDAsync(ID);
}

private async Task LoadProp2Async()
{
  Prop2 = await repo.GetProp2ByIDAsync(ID);
}