Change children pages data according to Tabbed page toolbar picker value change in Xamarin Forms - xamarin.forms

Question

I have a Tabbed page in my Xamarin Forms app. There I have two children content pages. There are two pickers and a button in the toolbar of the Tabbed page. What I want is to populate data from the server according to the values, which is changing in the pickers. I am using the MVVM design pattern. How can I pass picker values to the children pages? I tried to use the MessagingCenter, It works sometimes but not all the time.
Tabbedpage
public partial class LifekpiRankingTabbedRM : ZeroTabbarHeight
{
public LifekpiRankingTabbedRM(string uRegion)
{
InitializeComponent();
BindingContext = new LifekpiRankingRmTabbedViewModel(uRegion);
Children.Add(new LifeKpiRankingViewRM(uRegion));
Children.Add(new LifeKpiRankingViewRMsBM(uRegion));
}
}
Tabbedpage VM
public class LifekpiRankingRmTabbedViewModel : BaseViewModelHelper
{
public MonthData2 SelectedMonth
{
get => _selectedMonth;
set
{
_selectedMonth = value;
GenerateData(_selectedMonth.mIndex, SelectedKpi).Await(CompletedTask, ErrorHandle);
OnPropertyChanged();
}
}
public string SelectedKpi
{
get => _selectedKpi;
set
{
_selectedKpi = value;
GenerateData(SelectedMonth.mIndex, _selectedKpi).Await(CompletedTask, ErrorHandle);
OnPropertyChanged();
}
}
public LifekpiRankingRmTabbedViewModel(string uRegion)
{
this.uRegion = uRegion;
SelectedMonth = GetCurrentMonth();
SelectedKpi = KpiList.First();
reportType = "Monthly";
ReportTypeTapCommand = new Command(ChangeTypeCommand);
}
private async Task GenerateData(int selectedMonth, string selectedKpi)
{
AcrDialogClass.ShowLoadingDialog("Loading...");
if (runCount > 2)
{
var resRmData = await _apiServices.GetLifeRegionalKpiWiseRanking(selectedMonth, selectedKpi, isCumulative);
var resBmForRmData = await _apiServices.GetLifeBranchKpiWiseRankingForRM(selectedMonth, selectedKpi, uRegion, isCumulative);
if (resRmData != null)
{
MessagingCenter.Send<App, string>(App.Current as App, "KPI_REGINAL_RANKING", resRmData);
}
if (resBmForRmData != null)
{
MessagingCenter.Send<App, string>(App.Current as App, "KPI_BM_RANKING_FOR_RM", resBmForRmData);
}
}
else
{
runCount++;
}
}
private MonthData2 GetCurrentMonth()
{
var months = Enumerable.Range(1, 12).Select(i => new { I = i, M = DateTimeFormatInfo.InvariantInfo.GetMonthName(i) });
foreach (var ss in months)
{
MonthList.Add(new MonthData2() { mIndex = ss.I, mName = ss.M });
}
return MonthList.Find(r => r.mIndex == dt.Month);
}
private void ChangeTypeCommand()
{
if (isCumulative)
{
reportType = "Monthly";
isCumulative = false;
}
else
{
reportType = "Cumulative";
isCumulative = true;
}
GenerateData(SelectedMonth.mIndex, SelectedKpi).Await(CompletedTask, ErrorHandle);
}
private void CompletedTask()
{
AcrDialogClass.HideLoadingDialog();
}
private void ErrorHandle(Exception ex)
{
AcrDialogClass.HideLoadingDialog();
}
}
Tab 1
public partial class LifeKpiRankingViewRM : ContentPage
{
private LifeKpiRankingViewModelRM vm;
public LifeKpiRankingViewRM(string uRegion)
{
InitializeComponent();
BindingContext = new LifeKpiRankingViewModelRM(uRegion);
vm = BindingContext as LifeKpiRankingViewModelRM;
}
protected override void OnAppearing()
{
base.OnAppearing();
MessagingCenter.Subscribe<App, string>(App.Current, "KPI_REGINAL_RANKING", (snd, arg) =>
{
vm.SetValues(arg);
});
}
protected override void OnDisappearing()
{
base.OnDisappearing();
MessagingCenter.Unsubscribe<App, string>(App.Current, "KPI_REGINAL_RANKING");
}
}
Tab 2
public partial class LifeKpiRankingViewRMsBM : ContentPage
{
private LifeKpiRankingViewModelBMForRM vm;
public LifeKpiRankingViewRMsBM(string uRegion)
{
InitializeComponent();
BindingContext = new LifeKpiRankingViewModelBMForRM(uRegion);
vm = BindingContext as LifeKpiRankingViewModelBMForRM;
}
protected override void OnAppearing()
{
base.OnAppearing();
MessagingCenter.Subscribe<App, string>(App.Current, "KPI_BM_RANKING_FOR_RM", (snd, arg) =>
{
vm.SetValues(arg);
});
}
protected override void OnDisappearing()
{
base.OnDisappearing();
MessagingCenter.Unsubscribe<App, string>(App.Current, "KPI_BM_RANKING_FOR_RM");
}
}

Answer 1

At first, you can try to get the child page's instance and then set its value.
If you set the tabbedpage in the app.cs with MainPage = new LifekpiRankingTabbedRM():
var tabbedpage = App.Current.MainPage as LifekpiRankingTabbedRM;
var childpage1 = tabbedpage.Children[0];
var vm1 = childpage1.BindingContext as LifeKpiRankingViewModelRM;
vm1.SetValues(...);
Generally speaking, when you have the instance of the TabbedPage, you can get its child page and update the child page's value.
In addition, you can show more details about the MessageCenter not work and we can help you go on using the MessageCenter.