.Result（）使方法挂起时，如何在构造函数中使用异步方法？

Question

I have an AppearingCommand called when a Page appears in my Xamarin.Forms project, that eventually executes the following sqlite-net-pcl line: (I already have a mechanism coping with loading time)

AppearingCommand = new Command( async() => {
    //...
    var data = await db.Table<PlantCategory>().ToListAsync();
    //...
}

I want to move this method to the constructor, but I cannot do it, as it hangs if it is executed synchronously:

ctor() {
    //...
    var data = db.Table<PlantCategory>().ToListAsync().Result;
    //...
}

The line never returns (I am guessing because of a deadlock or something). What are other options that I have if I want to execute this line inside the constructor?

Answer 1

Simple. Don't.

Instead, add a post-construction method like async ValueTask InitAsync() and call that with await .

You could hide this behind a static ValueTask<Whatever> CreateAsync(...) method that you call instead of new Whatever(...) , ie

class Whatever {
    private Whatever(...) { ... } // basic ctor
    private async ValueTask InitAsync(...) { ... } // async part of ctor

    public static async ValueTask<Whatever> CreateAsync(...) {
        var obj = new Whatever(...);
        await obj.InitAsync(...);
        return obj;
    }
}