无法访问Blazor Server 3.0中的已处置对象 [英] Cannot access a disposed object in Blazor Server 3.0

问题描述

我有一个带有以下表单提交按钮的Blazor页面

 < button type = submit class = btn btn -primary @onclick = @（async（）=>等待OnCreateItem（））>创建< / button> 
  

哪个通话

 受保护的异步任务OnCreateItem（）
 {
 try 
 {
 
 var result = await dbMgr.CreateAsync（item）; 
} 
捕获（异常除外）
 {
抛出==>无法访问已处置的对象。导致此错误的常见原因是，处理从依赖项注入中解决的上下文，然后稍后尝试在应用程序中的其他位置使用相同的上下文实例。如果您正在调用Dispose（）... 
} 
} 
  

dbMgr注入到页面

  @inject DBManager dbMgr; 
  

管理器的实现方式为

  class DBManager 
 {
 ... 
 public DBManager（DBContext db）
 {
 _db = db; 
} 
 
公共异步任务< int> CreateAsync（ItemModel obj）
 {
等待_db.AddAsync（obj）; 
等待返回_db.SaveChangesAsync（）
} 
} 
  

启动类为

  public void ConfigureServices（IServiceCollection services）
 {
 services.AddRazorPages（）; 
 services.AddServerSideBlazor（）; 
 services.AddDbContext< DBContext>（options => 
 options.UseSqlServer（Configuration.GetConnectionString（ DBContext）），ServiceLifetime.Scoped）; 
 services.AddScoped< DBManager>（）; 
} 
  

我在这里读过类似的问题
链接1
链接2

无济于事。

不确定我在做什么错。

解决方案

我没有尝试您的代码，但是我想这是由于在

<$ p $中设置type = submit p> <按钮类型=提交 class = btn btn-primary @onclick = @（async（）=>等待OnCreateItem（））>创建< / button>


结果，当您按下创建按钮时，就会发生传统的回发。 ..也就是说，您的SPA应用回发到服务器。这种情况不应该发生（在这种情况下），因为您的应用重定向到限制基本uri之外的uri，然后返回，令人遗憾地发现OnCreateItem中的对象已失效（已处置）。只需设置type = button。

重要提示：据我回忆起过去，Blazor JavaScript中应该有代码可以防止此类事件发生：即回发到服务器。

I got a Blazor page with following form submit button

<button type="submit" class="btn btn-primary" @onclick="@(async()=> await OnCreateItem())">Create </button>

Which calls

protected async Task OnCreateItem()
{
    try
    {

        var result = await dbMgr.CreateAsync(item);
    }
    catch (Exception ex)
    {
         Throws ==> Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling Dispose()...
    }
}

dbMgr is injected to the page

@inject DBManager dbMgr;

And manager is implemented as

class DBManager 
{
...
    public DBManager(DBContext db)
    {
         _db = db;
    }

    public async Task<int> CreateAsync(ItemModel obj)
    {
        await _db.AddAsync(obj);
        return await _db.SaveChangesAsync()
    }
}

Startup class is

public void ConfigureServices(IServiceCollection services)
{
       services.AddRazorPages();
       services.AddServerSideBlazor();
       services.AddDbContext<DBContext >(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DBContext")),  ServiceLifetime.Scoped);
       services.AddScoped<DBManager>();
 }

I read a similar questions here Link 1 Link 2

To no avail.

Not sure what am I doing wrong.

解决方案

I did not try your code, but I guess it is due to setting type="submit" in

<button type="submit" class="btn btn-primary" @onclick="@(async()=> await OnCreateItem())">Create </button>

As a result, when you hit the "Create" button, a traditional post back takes place. .. that is, your SPA app post back to the server. It shouldn't happen (in that case), as your app redirects to a uri outside of the limiting base uri, and then returns back, sadly enough to find the objects in the OnCreateItem dead (disposed). Just set type="button".

Important: As far as I recall from days bygone, there should be code in Blazor JavaScript to prevent such incidents: that is posting back to the server.

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