How would you call async method in a method which cannot be async in C# without using .Result

问题

I am overriding a method, HandleRequirementAsync, so I can't modify the return type of that method. However, I am calling a method in UserManager which is async and requires an await so I had to put this code in another method.

        protected override Task HandleRequirementAsync(
          AuthorizationHandlerContext context,
          EducationArmRequirement requirement)
        {

            if (!IsEducationGroup(context).Result)
            {
                return Task.FromResult(0);
            }


            context.Succeed(requirement);

            return Task.FromResult(0);
        }

        protected async Task<bool> IsEducationGroup(AuthorizationHandlerContext context)
        {
            var userId = context.User.Identity.Name;
            ApplicationUser u = await _userManager.FindByNameAsync(userId);
            if (u.Group == 3 || u.Group == 4)
            {
                return await Task.FromResult(true);
            }
            return await Task.FromResult(false);
        }

The code above seems to work in testing but it uses .Result to unwrap the Task to get the bool. I have seen several places that say be careful of using result. I saw this question which tries to explain why but I am not getting it.

I can't put an await in the HandleRequirementAsync method to allow this to unrap normally because then I would have to modify the return type which I can't do for this overridden method.

Am I approaching this the correct way in using the .Result or am I going to come across some issues here and if so what is another way to approach this which would work?

Any help/explanations would be much appreciated.

回答1:

As hinted in the comments, the async modifier doesn't change the method signature - you can just add this. You can also simplify to remove usage of Task.FromResult in both methods:

protected override async Task HandleRequirementAsync(
    AuthorizationHandlerContext context,
    EducationArmRequirement requirement)
{
    if (await IsEducationGroup(context))
    {
        context.Succeed(requirement);
    }
}

protected async Task<bool> IsEducationGroup(AuthorizationHandlerContext context)
{
    var userId = context.User.Identity.Name;

    ApplicationUser u = await _userManager.FindByNameAsync(userId);

    return u.Group == 3 || u.Group == 4;
}

回答2:

IsEducationGroup group function

protected async Task<bool> IsEducationGroup(AuthorizationHandlerContext context)
{ 
await Task.Run((){

            var userId = context.User.Identity.Name;
            ApplicationUser u = await _userManager.FindByNameAsync(userId);
            if (u.Group == 3 || u.Group == 4)
            {
                return true;
            }
            return false;
        }

    })

HandleRequirementAsync function

protected override async Task HandleRequirementAsync(
          AuthorizationHandlerContext context,
          EducationArmRequirement requirement)
        {

           var result =  await (!IsEducationGroup(context));
            if(!result)
                return;


            context.Succeed(requirement);
            return;
        }

来源：https://stackoverflow.com/questions/38681091/how-would-you-call-async-method-in-a-method-which-cannot-be-async-in-c-sharp-wit