CS1988|C#无法在异步方法中使用ref,in,out类型的参数的问题

news2024/9/17 7:24:34

CS1988|C#无法在异步方法中使用ref,in,out类型的参数

🌀|场景：

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BlazorServer的场景中推荐使用异步方法，使用ref,out,in为参数前缀则报错CS1988

原因如下:

ref parameters are not supported in async methods because the method may not have completed when control returns to the calling code. Any changes to the referenced variables will not be visible to the calling code, resulting in a CS1988 error.

async 方法不支持 ref 参数，因为当控件返回到调用代码时，该方法可能尚未完成。对引用变量的任何更改都对调用代码不可见，从而导致 CS1988 错误。

⛵️|替代方法：

将需要用到的参数作为Task的返回，即

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💥|延申：引用变量的可见性

1.当不使用基础类型为参数，使用引用类型时：

现有Blazor页面如下

@page "/login"

@using KatexTest2.Models
@using KatexTest2.Utils
@inject MyAuthProvider provider


<h3>LoginPage</h3>

<AuthorizeView>
    <NotAuthorized>
        
        @if(Isfailed){
            <span>用户名或密码错误</span>
        }
        
        @if (test.Number==114.514M)
        {
            <span>压力吗室内</span>
        }
        <EditForm id = "LP" Model="loginModel" Context="Login">
            <div>
                <label> Username: 
                    <InputText @bind-Value="loginModel.Username"></InputText>
                </label>
            </div>
            <div>
                <label> Password:
                    <InputText type="password" @bind-Value="loginModel.Password"></InputText>
                </label>
            </div>
            <div>
                <button @onclick="TryLogin">Submit</button>
            </div>
        </EditForm>    
    </NotAuthorized>
    <Authorized>
        <button type="button" class="btn btn-primary" @onclick="TryLogout" ></button>
    </Authorized>    
    <Authorizing>
        <span>翼沿丁真</span>
    </Authorizing>
</AuthorizeView>


@code {

    public class RefTest
    {
        public string Context { get; set; } = "DefaultContext";

        public decimal Number { get; set; } = 11.54M;
    }

    [Parameter]
    public Boolean Isfailed { get; set; } = false;

    public RefTest test { get; set; } = new();

    private LoginFormModel loginModel { get; set; } = new();

    private async Task TryLogin()
    {
        
       Isfailed  =  await provider.LoginAsync(loginModel,test);
        
    }

    private async Task TryLogout()
    {
        await provider.LogoutAsync();
    }
}

修改LoginAsync方法如下:

 public async Task<Boolean> LoginAsync(LoginFormModel loginFormModel,RefTest test)
{
    var (userInDatabase, isSuccess) = LookUpUser(loginFormModel.Username, loginFormModel.Password);
    var principal = new ClaimsPrincipal();

    if (isSuccess)
    {
        var identity = CreateIdentityFromUser(userInDatabase);
        principal = new ClaimsPrincipal(identity);
        await _protectedLocalStorage.SetAsync("identity", JsonConvert.SerializeObject(userInDatabase));
    }
    else
    {
        test.Number = 114.514M;
    }

    NotifyAuthenticationStateChanged(Task.FromResult(new AuthenticationState(principal)));

    await jsRuntime.InvokeVoidAsync("alert", new object[1] { "WTF" });

    return !isSuccess;
}