How Redirect the page the in blazor Class file

Question

If using Navigatiomanager null value exception came while using in Class file

NavigationManager navigationManager;
  public ICollection<TimeOff> GetTimeOffbyStaff(int id)
    {
      ICollection<TimeOff> timeOff = new List<TimeOff>();
      try
      {
        timeOff = labOrgDbContext.TimeOff.Include(x => x.Technologist).Where(x => x.TechnologistId == id && x.FromDate >= (DateTime.Now.AddYears(-1)).Date && x.IsDeleted != true).OrderByDescending(x => x.RowInsertOn).ToList();
      }
      catch (Exception ex)
      {
        ExceptionLogging.SendErrorToText(ex, "1");
        navigationManager.NavigateTo("/PagenotFound");
        throw ex;
      }
      return timeOff;
    }

Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — jazb, Nov 27 '19 at 06:20
also read: https://learn.microsoft.com/en-us/aspnet/core/blazor/dependency-injection?view=aspnetcore-3.0 — jazb, Nov 27 '19 at 06:21
Object reference not set to an instance of an object. error come on this line 'navigationManager.NavigateTo("/PagenotFound");' — novfal haq, Nov 27 '19 at 06:47
have a look at `why` the object is `null` - clue...read my link on dependency injection above — jazb, Nov 27 '19 at 06:49

rk72 · Answer 1 · 2019-11-27T18:02:33.387

1

Refactor your code to not mix logic together with page navigation. Ie. have one class that will provide the "time off by staff" calculation. Then use that class in a visual page that will inject NavigationManager, and do the page navigation in case of error like this:

@page "/"
@inject NavigationManager navigationManager; // inject an instance of NavigationManager

<h1>Time-off by staff</h1>

Some page content.....

<button @onclick="GetTimeOffByStaff">Get time off by staff</button>

@code {
    void GetTimeOffByStaff()
    {
        try
        {
            TimeOffLogic logic = new TimeOffLogic();    // this will be your logic class

            var timeOff = logic.GetTimeOffbyStaff(id);
        }
        catch (Exception ex)
        {
            ExceptionLogging.SendErrorToText(ex, "1");
            navigationManager.NavigateTo("/PagenotFound");      // use NavigationManager
        }

        // do something with timeOff
    }
}

edited Nov 27 '19 at 18:02

answered Nov 27 '19 at 06:47

rk72

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thanks Actually i want to redirect while exception happen in my class method due to that i try to do in class instead of component – novfal haq Nov 27 '19 at 06:50
@novfalhaq Then simply pass the `navigationManager` instance to the `TimeOffLogic` constructor, and then call it's `NavigateTo()` method. That will work too. – rk72 Nov 27 '19 at 11:39
NullReferenceException: Object reference not set to an instance of an object. private readonly NavigationManager navigationManager; public TaskSchedulerService(NavigationManager navigationManager,) { this.navigationManager = navigationManager; } – novfal haq Nov 27 '19 at 12:26
@novfalhaq How/when you inject the NavigatorManager? Did you use the same code as in the example above, ie. ` [Inject] public NavigationManager navigationManager { get; set; } `? If so, if you put a breakpoint on the call to the TaskSchedulerService constructor, are you seeing a non-null value of the navigationManager property? – rk72 Nov 27 '19 at 12:36

How Redirect the page the in blazor Class file

1 Answers1