Razor 异步获取的页面 model 是 null

Question

I'm having interesting problem with Razor pages on Asp.Net Core 2.2. I have a page (not partial, normal page) with async get:

    public async Task<IActionResult> OnGetAsync()
    {
        Accounts = new List<DbAccount>();

        AccountRequest accountRequest = new AccountRequest(User.FindFirst("BearerToken").Value);
        await ClientRequest.ExecuteRequest(accountRequest);

        if (accountRequest.StatusCode != HttpStatusCode.OK)
        {
            ModelState.AddModelError("ERROR", "Login error");
            return Page();
        }
        else
        {
            var data = JsonConvert.DeserializeObject<List<DbAccount>>(accountRequest.ResponseContent);
            Accounts.AddRange(data);
            return Page();
        }
    }

Get is executed normally and there is data to add in Accounts.AddRange() but later in page, when I try to iterate over that collection, Model is null.

 @foreach(var account in Model.Accounts)
 {
     <tr>
     ...
     </tr>
 }

And of course, I get NullReferenceException on Model.Accounts. Where is the problem? In same project, in normal Get without async, Model is not null. Propery Accounts is set as BindProperty .

What I'm doing wrong?

Answer 1

Did you try to add a new razor page item to test? If _ everything else is "standard"_, it should get the value normally.

There is no actual difference between OnGet and OnGetAsync . OnGetAsync is just a naming convention for methods that contain asynchronous code that should be executed when a GET request is made. You can omit the Async suffix but still make the method asynchronous:

public async Task OnGet()
{
    ...
    await ....
    ...
}

Asynchronous methods are ones that free up their threads while they are executing so that it can be used for something else until the result of the execution is available. You can read more about how asynchronous methods work here: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/#BKMK_WhatHappensUnderstandinganAsyncMethod

You can't have an OnGet and an OnGetAsync handler in the same Razor Page. The framework sees them as being the same.

Answer 2

Problem solved by changing from async Task<IActionResult to async Task (and removing returns). Anyone can explain what is the difference and why it helped?

Answer 3

I had the same problem with public async void OnGetAsync() As soon as I added an await in het function I got a nullreference exception on the model.

Replacement with public async Task OnGetAsync() did solve my exception.