Exception on Xamarin: System.ObjectDisposedException: Cannot access a disposed object 'Xamarin.Forms.Platform.Android.FastRenderers.LabelRenderer'

Question

I am using Xamarin.Forms to build an app for Android and I'm currently getting the following error: System.ObjectDisposedException: Cannot access a disposed object 'Xamarin.Forms.Platform.Android.FastRenderers.LabelRenderer'. The Xamarin.Forms version I am using is 4.8.0.1364

My code for the XAML is the following:

The code for the ViewModel

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Input;
using Peripass.ApiModels;
using Peripass.Mobile.Framework.DependencyInterfaces;
using Peripass.YardAssetManagementApp.Data;
using Peripass.YardAssetManagementApp.Data.LocalDataServices;
using Peripass.YardAssetManagementApp.Data.Syncing.QueueItemSyncActions;
using Peripass.YardAssetManagementApp.DomainModel.V1;
using Peripass.YardAssetManagementApp.DomainModel.V1.Extensions;
using Peripass.YardAssetManagementApp.Events;
using Peripass.YardAssetManagementApp.Icons;
using Peripass.YardAssetManagementApp.Models;
using Peripass.YardAssetManagementApp.MVVM;
using Peripass.YardAssetManagementApp.UI.TopHeaders;
using Xamarin.Forms;

namespace Peripass.YardAssetManagementApp.ViewModels {
  public class MainTaskListViewModel : ViewModelBase {
    private readonly ILocalTaskDataService _localTaskDataService;
    private readonly ILocalLocationDataService _localLocationDataService;
    private readonly IToMobileTasksSyncer _toMobileTasksSyncer;
    private List _tasks;
    private readonly ILocalUserDataService _localUserDataService;

    public MainTaskListViewModel(ILocalTaskDataService localTaskDataService, ILocalLocationDataService localLocationDataService, IToMobileTasksSyncer toMobileTasksSyncer, ILocalUserDataService localUserDataService) {
      _localTaskDataService = localTaskDataService;
      _localLocationDataService = localLocationDataService;
      _toMobileTasksSyncer = toMobileTasksSyncer;
      _localUserDataService = localUserDataService;
      MessagingCenter.Unsubscribe(this, EventTypes.FetchingTasks.ToString());
      MessagingCenter.Unsubscribe(this, EventTypes.LocalTasksUpdated.ToString());
      MessagingCenter.Unsubscribe(this, EventTypes.LocalTasksUpdated.ToString());
      MessagingCenter.Unsubscribe(this, EventTypes.FetchingTasksFailed.ToString());
      SubscribeToTaskFetches();
      _tasks = new List();
    }
    public ICommand TappedGotoTaskDetailCommand => new Command(async (taskId) => await ExecuteGotoTaskDetail(taskId));
    public ICommand RefreshCommand => new Command(ExecuteRefreshCommand);

    private void SubscribeToTaskFetches() {
      MessagingCenter.Subscribe(this, EventTypes.FetchingTasks.ToString(), sender => {
        Model.ShowLoadingIndicator = true;
      });
      MessagingCenter.Subscribe(this, EventTypes.LocalTasksUpdated.ToString(), _ => OnTasksUpdated());
      MessagingCenter.Subscribe(this, EventTypes.LocalTasksUpdated.ToString(), _ => OnTasksUpdated());
      MessagingCenter.Subscribe(this, EventTypes.FetchingTasksFailed.ToString(), sender => {
        Model.ShowLoadingIndicator = false;
      });
    }

    private void OnTasksUpdated() {
      Model.ShowLoadingIndicator = false;
      GetTasks();
      MapToModel();
    }

    public bool IsRefreshing { get; set; }

    private async void ExecuteRefreshCommand() {
      try {
        if (IsRefreshing) {
          return;
        }

        IsRefreshing = true;
        await _toMobileTasksSyncer.SyncAllData();
      }
      catch {
        await NavigationService.NavigateToViewModelAsync();
      }
      finally {
        IsRefreshing = false;
      }
    }

    public override void OnInit(object param) {
      SetTopHeader();
    }

    private void SetTopHeader() {
      var topHeader = new TopHeaderForAllTasksContentView(SearchTextChangedAction, StopSearchAction);
      topHeader.SetLine("Task List");
      NavigationService.SetTopHeader(TopHeaderTappedBackCommand, topHeader);
      NavigationService.SetTopHeaderVisible(true);
    }

    public override void OnAppeared() {
      GetTasks();
      MapToModel();
    }

    private void GetTasks() {
      _tasks = _localTaskDataService
        .GetAllTasks()
        .Where(task => task.Status == TaskStatusEnum.Unassigned || task.Status == TaskStatusEnum.Started && task.AssignedOperatorId == _localUserDataService.GetCurrentUser().UserTechnicalId)
        .ToList();
    }

    private async Task ExecuteGotoTaskDetail(int taskId) {
      await NavigationService.NavigateToViewModelAsync(taskId);
    }

    private void StopSearchAction() {
      DependencyService.Get().HideKeyboard();
      MapToModel();
    }

    private void SearchTextChangedAction(string searchText) {
      MapToModel(searchText);
    }

    private void TopHeaderTappedBackCommand() {
      NavigationService.ShowMenu();
    }

    private void MapToModel(string searchOn = "") {
      Model.IsSearching = searchOn != "";
      Model.AllTasks = new ObservableCollection();
      Model.ShowMessageNoTasksAvailable = !Model.ShowLoadingIndicator && _tasks.All(task => task.Status == TaskStatusEnum.Finished);
      AddUncompletedTasks(searchOn);
    }

    private void AddUncompletedTasks(string searchOn = "") {
      if (_tasks == null) return;
      var tasks = _tasks.Where(c => c.Status != TaskStatusEnum.Finished).ToArray();
      if (searchOn != "") {
        tasks = _tasks.Where(task => task.GetSearchableTaskString(_localLocationDataService.GetLocations()).Contains(searchOn.ToUpper(CultureInfo.InvariantCulture))).ToArray();
      }

      for (var i = 0; i < tasks.Length; i++) {
        AddUncompletedTask(i, tasks[i]);
      }
    }

    private void AddUncompletedTask(int index, YardOperatorTask task) {
      var rowBackgroundColor = Color.FromHex("FFFFFF");
      if (index % 2 == 0) {
        rowBackgroundColor = Color.FromHex("F6F6F6");
      }

      var leftIconChar = CalcLeftIconChar(task);
      var iconColor = CalcIconColor(task);
      var rightIconChar = CalcRightIconChar(task);

      var stepProgressLineStepsDone = task.TaskSteps.Count(c => c.IsDone).ToString();
      var stepProgressLineStepsTotal = task.TaskSteps.Count().ToString();

      Model.AllTasks.Add(new TaskItem {
        TaskIsFinished = false,
        TaskId = task.Id,
        LeftIconChar = leftIconChar,
        LeftIconColor = iconColor,
        TaskLine1 = task.GetTaskDisplayName(_localLocationDataService.GetLocations()),
        TaskLine2 = task.Template.Name,
        RightIconChar = rightIconChar,
        RightIconColor = iconColor,
        RowBackGroundColor = rowBackgroundColor,
        StepProgressLineStepsDone = stepProgressLineStepsDone,
        StepProgressLineStepsTotal = stepProgressLineStepsTotal,
        DisplayName = task.Asset?.Name ?? task.Visitor.Name
      });
    }

    private static char CalcRightIconChar(YardOperatorTask task) {
      switch (task.Status) {
        case TaskStatusEnum.Unassigned:
          return IconChar.For(IconsEnum.TaskListTaskIsUnassiged);
        case TaskStatusEnum.Assigned:
        case TaskStatusEnum.Started:
          return IconChar.For(IconsEnum.TaskListTaskStarted);
        default:
          return ' ';
      }
    }

    private static Color CalcIconColor(YardOperatorTask task) {
      switch (task.Status) {
        case TaskStatusEnum.Unassigned:
          return IconColor.For(IconsEnum.TaskListTaskIsUnassiged);
        case TaskStatusEnum.Assigned:
        case TaskStatusEnum.Started:
          return IconColor.For(IconsEnum.TaskListTaskStarted);
        default:
          return Color.Black;
      }
    }

    private static char CalcLeftIconChar(YardOperatorTask task) {
      if (task.TaskSteps.Any(c => c.FieldDefinitionType == FieldDefinitionType.MoveToLocation)) {
        return IconChar.For(IconsEnum.TaskListTaskIsMove);
      }
      else {
        return IconChar.For(IconsEnum.TaskListTaskIsInspection);
      }
    }
  }
}

I believe that this piece of code in the XAML is the culprit. More specific, the IsVisible property of the label. If I remove that, the exception does not seem to happen.

I have searched for some time now and tried different things but nothing seems to work. If you need more information, please do ask.

nevermore · Accepted Answer

This issue has been fix in the latest version of Xamarin.forms 4.8.0.1687.

Any one who meet this issue please update your Xamarin.forms version.

Here are some relevant threads in the Github.

Cannot access a disposed object

Cannot access a disposed object FastRenderers.LabelRenderer

Exception on Xamarin: System.ObjectDisposedException: Cannot access a disposed object 'Xamarin.Forms.Platform.Android.FastRenderers.LabelRenderer'

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Exception on Xamarin: System.ObjectDisposedException: Cannot access a disposed object 'Xamarin.Forms.Platform.Android.FastRenderers.LabelRenderer'