如何等待运行异步方法的任务

Question

我正在编写 WPF 应用程序，最近开始使用 await/async，因此 GUI 线程不会执行任何耗时的操作。

我的问题是我想使用实体框架从 db 异步加载两个集合。我知道我不能在 DbContext 上调用两个 ToListAsync() 方法，所以我想使用任务。

我编写了异步方法LoadData()，它应该等待完成LoadNotifications()，然后调用LoadCustomers()。

但是当执行到await this.context.MailingDeliveryNotifications.ToListAsync(); 时，它会创建另一个任务，并且不知何故它不关心我的LoadData() 方法中的task.Wait()，因此它在完成对DbContext 的第一次调用之前调用LoadCustomers()。

代码：

    public async void LoadData()
    {
        Task task = this.LoadNotifications();
        task.Wait();
        await this.LoadCustomers();
    }

    private Task LoadNotifications()
    {
        return Task.Run(() => this.LoadNotificationsAsync());
    }

    private async void LoadNotificationsAsync()
    {
        List<MailingDeliveryNotification> res = await this.context.MailingDeliveryNotifications.ToListAsync();
        this.Notifications = new ObservableCollection<MailingDeliveryNotification>(res);
    }

    private Task LoadCustomers()
    {
        return Task.Run(() => this.LoadNotificationsAsync());
    }

    private async void LoadCustomersAsync()
    {
        List<Customer> res = await this.context.Customers.ToListAsync();
        this.Customers = new ObservableCollection<Customer>(res);
    }

我知道我可以使用此代码解决此问题

    public async void LoadData()
    {
        List<MailingDeliveryNotification> res = await this.context.MailingDeliveryNotifications.ToListAsync();
        this.Notifications = new ObservableCollection<MailingDeliveryNotification>(res);

        List<Customer> res2 = await this.context.Customers.ToListAsync();
        this.Customers = new ObservableCollection<Customer>(res2);
    }

但是当我需要添加另一个集合以从 db 加载时，这种方法会增长很多。我想保持我的代码干净。

Answer 1

简化您的代码：

public async Task LoadDataAsync()
{
    await LoadNotificationsAsync();
    await LoadCustomersAsync();
}

private async Task LoadNotificationsAsync()
{
    var res = await context.MailingDeliveryNotifications.ToListAsync();
    Notifications = new ObservableCollection<MailingDeliveryNotification>(res);
}

private async Task LoadCustomersAsync()
{
    var res = await context.Customers.ToListAsync();
    Customers = new ObservableCollection<Customer>(res);
}

或者可能只是：

public async Task LoadDataAsync()
{
    Notifications = new ObservableCollection<MailingDeliveryNotification>(
        await context.MailingDeliveryNotifications.ToListAsync());

    Customers = new ObservableCollection<Customer>(
        await context.Customers.ToListAsync());
}