what is the proper way of subscribing to a ReactiveCommand in ReactiveUI 8.2 - reactive-programming

Question

I have following snippet in ViewModel.
public ReactiveCommand<object, System.Reactive.Unit> LoadCustomerDetails;
ReactiveCommand<OrderViewPager<SalesOrderOrderOptionsEnum>, CommandSubmitResultDto<List<SalesOrderDto>>> _loadSalesOrderList;
public ReactiveCommand<OrderViewPager<SalesOrderOrderOptionsEnum>, CommandSubmitResultDto<List<SalesOrderDto>>> LoadSalesOrderList
{
get { return _loadSalesOrderList; }
private set { this.RaiseAndSetIfChanged(ref _loadSalesOrderList, value); }
}
this.LoadSalesOrderList = ReactiveCommand.CreateFromTask<Pager<OrderOptionsEnum>, CommandSubmitResultDto<List<SalesOrderDto>>>(
async filter =>
{
Debug.WriteLine("Load SalesOrderList...");
Debug.WriteLine("Customer Id : " + SelectedCustomerId);
await LoadCustomerDetails.Execute();
var result = await SalesOrderMobApi.GetByCustomerTraderEntityIdPaged(SelectedCustomerId, filter, null, SalesOrderTypeEnum.SalesOrder, SalesOrderPOOptions.NotOriginatingFromPurchaseOrder);
return result;
})
.DisposeWith(ViewModelBindings.Value);
this.LoadSalesOrderList.ThrownExceptions
.Subscribe(ex =>
{
Debug.WriteLine("Load SalesOrderList Failed!");
});
this.LoadSalesOrderList
.ObserveOn(RxApp.MainThreadScheduler)
.Subscribe(result =>
{
if (result.PagingInfo.CurrentPage > 1)
{
foreach (var item in result.Data)
{
SalesOrdersList.Add(SalesOrderVMM.From(item));
}
}
else
{
SalesOrdersList.Clear();
foreach (var item in result.Data)
{
SalesOrdersList.Add(SalesOrderVMM.From(item));
}
}
});
LoadCustomerDetails = ReactiveCommand.CreateFromTask<object, System.Reactive.Unit>(
async _ =>
{
Debug.WriteLine(SelectedCustomerId);
var customers = await TraderEntityMobApi.GetById(SelectedCustomerId);
var customer = customers.Data;
SelectedCustomer = customer;
return System.Reactive.Unit.Default;
}
).DisposeWith(ViewModelBindings.Value);
It sometimes gives exception as follows.
System.NullReferenceException: Object reference not set to an instance of an object.
06-20 16:05:02.480 I/MonoDroid(15304): at DistributrIII.Mobile.Lib.VM.SalesOrder.CreateSOListVM.<RegisterObservables>b__43_2 (System.Collections.Generic.List`1[T] result) [0x0000e] in C:\Users\gayanbu\Source\Repos\Distributr 3.0 UI\Mobile\DistributrIII.Mobile.Lib\VM\SalesOrder\CreateSOListVM.cs:131 .at System.Reactive.AnonymousSafeObserver`1[T].OnNext (T value) [0x0000a] in <99f8205c51c44bb480747b577b8001ff>:0
06-20 16:05:02.480 I/MonoDroid(15304): at System.Reactive.ScheduledObserver`1[T].Run (System.Object state, System.Action`1[T] recurse) [0x000f5] in <99f8205c51c44bb480747b577b8001ff>:0
06-20 16:05:02.480 I/MonoDroid(15304): at System.Reactive.Concurrency.Scheduler+<>c__DisplayClass49_0`1[TState].<InvokeRec1>b__0 (TState state1) [0x0001e] in <99f8205c51c44bb480747b577b8001ff>:0
06-20 16:05:02.480 I/MonoDroid(15304): at System.Reactive.Concurrency.Scheduler.InvokeRec1[TState] (System.Reactive.Concurrency.IScheduler scheduler,
I guess it tries to execute the code inside reactive command ,LoadSalesOrderList even the result of this is null. How to handle this ? Could someone kindly explain the proper way of subscribing to Reactive Command. I am executing this command in the page load as, this.ViewModel.LoadSalesOrderList.Execute().subscribe(new Pager<OrderOptionsEnum>())
Thanks!

Answer 1

if you want your command when throw exception to be catched in ThrownExceptions execute command like Observable.Return(input).InvokeCommand(Command).DisposeWith(disposable) where input is the input for command and Command is the name of the Command