How to call asynchronous method in class constructor?

Constructors can not be marked as async . There is a open discussion in the GitHub C # repository on the subject.

That said, there is no way to call a method and wait for it with the keyword await .

An alternative is to create a static method that constructs the object. See in the example:

public static async Task<Foo> Construir() {
    await MetodoAssincrono(); // chamada assíncrona
    return new Foo(); // retorna instância do objeto construído
}

If you need to populate something inside the instance that comes from the return of this asynchronous method, do something like this:

public static async Task<Foo> Construir() {
    var instancia = new Foo(); // constrói objeto
    instancia.Dados = await GetDadosAsync(); // preenche o que precisa preencher; chamada assíncrona
    return instancia; // retorna instância do objeto construído
}

Instead of

var obj = new Foo();

you would have

var obj = await Foo.Construir();

If you do not want a static method, create an asynchronous boot function within your class. After the object is built, call it:

var obj = new Foo();
await obj.Inicializar(); // Inicializar() retorna uma Task que será consumida aqui