How can I call async method from constructor?

问题

I need to call a async method from my Form1 constructor. Since a constructor can't have a return type, I can't add a async void. I read that static constructor can be async but I need to call methods from constructor that aren't static, such as InitializeComponent() (since it's the Form's constructor).

The class is:

public partial class Form1 : Form
{
    InitializeComponent();
    //some stuff
    await myMethod();
}

I read this one too but I still don't know how to implement this (in my case) since the method still requires to use async.

回答1:

Don't do this in the constructor but in the loaded event of the window instead. You can mark the loaded eventhandler as async.

回答2:

You can use a static method that returns an instance of your form

public class TestForm : Form
{
    private TestForm()
    {
    }

    public static async Task<TestForm> Create()
    {
        await myMethod();
        return new TestForm();
    }
}

回答3:

My sample is to call student details from page constructor

1- the calling of navigation page

    void Handle_ItemTapped(object sender, Xamarin.Forms.ItemTappedEventArgs e)
    {
        Student _student = (Student)e.Item;
        Navigation.PushAsync(new Student_Details(_student.ID));

    }

2 - the details page

public partial class Student_Details : ContentPage
{
    public Student_Details(int id)
    {
        InitializeComponent();
        Task.Run(async () => await getStudent(id));
    }

    public async Task<int> getStudent(int id)
    {
        Student _student;
        SQLiteDatabase db = new SQLiteDatabase();
        _student = await db.getStudent(id);
        return 0;
    }
}

回答4:

While common advice dictates you generally shouldn't do it in the constructor, you can do the following, which I have used in apps, such as console apps, where I need to call some existing async code:

DetailsModel details = null; // holds the eventual result
var apiTask = new Task(() => details = MyService.GetDetailsAsync(id).Result); // creates the task with the call on another thread
apiTask.Start(); // starts the task - important, or you'll spin forever
Task.WaitAll(apiTask); // waits for it to complete

Philip is correct that, if you can avoid doing this in a constructor, you should.

回答5:

Task.Run(async () => await YourAsyncMethod());

来源：https://stackoverflow.com/questions/29054202/how-can-i-call-async-method-from-constructor

标签

winforms

constructor

async-await