how to use pagination in group listview - xamarin.forms

Question

I am using ItemAppearing method pagination in normal listview. but I developed the same code in group listview. But it is a crash. How to use the ItemAppearing method in grouped Listview. Anyone guide me for this scenario. I Paste my code for ur reference.
<ListView x:Name="CustomerListview" ItemAppearing="Handle_ItemAppearing"
IsVisible="true" Footer="" IsGroupingEnabled="true" BackgroundColor="Transparent" Margin="0,10,0,10" SeparatorVisibility="None" HasUnevenRows="True" VerticalOptions="FillAndExpand" HorizontalOptions="CenterAndExpand" >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell Height="80">
<StackLayout
Margin="20,0,0,0" Spacing="0" Padding="0"
Orientation="Horizontal"
VerticalOptions="FillAndExpand">
<StackLayout
x:Name="firstStackLayout"
Margin="0,0,0,-6"
HorizontalOptions="Center"
Orientation="Vertical"
VerticalOptions="FillAndExpand">
<BoxView
Grid.Row="0"
Grid.Column="0"
Margin="0,0,0,-6"
HeightRequest="30"
HorizontalOptions="Center"
WidthRequest="2"
VerticalOptions="FillAndExpand"
Color="#b11541" />
<BoxView
Grid.Row="1"
Grid.Column="0"
Margin="0,0,0,0"
HeightRequest="20"
CornerRadius="10"
BackgroundColor="Gray"
WidthRequest="20">
<!--<ff:CachedImage.Transformations>
<ffTransformations:RoundedTransformation
BorderHexColor=""
BorderSize="20"
Radius="240" />
</ff:CachedImage.Transformations>-->
</BoxView>
<BoxView
Grid.Row="2"
Grid.Column="0"
Margin="0,-6,0,0"
HeightRequest="30"
HorizontalOptions="Center"
IsVisible="true"
WidthRequest="2"
VerticalOptions="FillAndExpand"
Color="#b11541" />
</StackLayout>
<StackLayout
Margin="10,15,5,0"
HorizontalOptions="Start"
Orientation="Vertical"
VerticalOptions="Center">
<Label
FontAttributes="Bold"
FontSize="15"
HorizontalOptions="Start"
Text="{Binding Lease_refno}"
TextColor="#b11541"
XAlign="Start" />
<StackLayout
Margin="0,0,5,0"
Orientation="Horizontal"
VerticalOptions="EndAndExpand">
<Label
FontSize="14"
Text="{Binding Billing_start_date}"
TextColor="#4e5156" />
</StackLayout>
</StackLayout>
<StackLayout.GestureRecognizers>
<TapGestureRecognizer Tapped="leaseClicked"/>
</StackLayout.GestureRecognizers>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
<ListView.GroupHeaderTemplate>
<DataTemplate>
<ViewCell Height="55">
<StackLayout BackgroundColor="Transparent" Padding="5, 5, 5, 0">
<Frame Margin="5,0,5,5" HasShadow="False" IsClippedToBounds="true" BorderColor="Transparent" BackgroundColor="Transparent" CornerRadius="5" Padding="0">
<Grid RelativeLayout.XConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width, Factor=0.25}"
RelativeLayout.WidthConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width, Factor=0.75}"
BackgroundColor="White" ColumnSpacing="0" RowSpacing="0">
<Grid.RowDefinitions>
<RowDefinition Height="5"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="30"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<StackLayout BackgroundColor="White" VerticalOptions="FillAndExpand" Grid.Row="0" Grid.RowSpan="8">
<BoxView HorizontalOptions="Start" WidthRequest="5" BackgroundColor="#b11541" VerticalOptions="FillAndExpand"/>
</StackLayout>
<Label Text="{Binding Customer_company}" TextColor="Black"
FontSize="14" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="7"
x:Name="originEntry" Margin="20,5,0,5"
VerticalOptions="Start" FontFamily="{StaticResource OpenSansBold}"
HorizontalOptions="FillAndExpand" />
<!--<StackLayout Spacing="0" Grid.Column="0" Padding="0" Margin="0,0,0,10" Grid.Row="2" Orientation="Horizontal">
<Label Text="View Lease" Padding="5,0,5,0" TextColor="White" BackgroundColor="#97304d"
Grid.ColumnSpan="4" FontFamily="{StaticResource OpenSansSemiBold}" Margin="20,0,0,0" FontSize="12"
x:Name="destinationEntry" VerticalOptions="Start"
HorizontalOptions="Start" >
<Label.GestureRecognizers>
<TapGestureRecognizer Tapped="leaseClicked"/>
</Label.GestureRecognizers>
</Label>
</StackLayout>-->
<Grid.GestureRecognizers>
<TapGestureRecognizer NumberOfTapsRequired="1" CommandParameter="{Binding .}" Tapped="HeaderTapped"/>
</Grid.GestureRecognizers>
</Grid>
</Frame>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.GroupHeaderTemplate>
</ListView>
private async void Handle_ItemAppearing(object sender, Xamarin.Forms.ItemVisibilityEventArgs e)
{
var currentIdx = Items.IndexOf((ProductColor)e.Item);
if (currentIdx > _lastItemAppearedIdx)
{
if (Items.Count == 0)
return;
var selectedItem = e.Item as ProductColor;
//hit bottom!
if (isLoading == false && selectedItem == ResultList[ResultList.Count - 1])
{
i++;
await UserTweetsList("lease", "");
}
}
_lastItemAppearedIdx = Items.IndexOf((ProductColor)e.Item);
}

Answer 1

var currentIdx = Items.IndexOf((ProductColor)e.Item
Actually , in the event ItemAppearing you could get the index of current appearing item directly like
int currentIdx = e.ItemIndex ;
And improve the code like :
In group ListView the index with equal -1 when the first item appearing .
if(currentIdx !=-1)
{
// if...
}
In addition , from your code I could not see the part of group . So it could be better to share your sample which contains the issue so that I can test it on my side .
Update
private void CusHandle_ItemAppearing(object sender, Xamarin.Forms.ItemVisibilityEventArgs e)
{
// var currentIdx = customerList.IndexOf((ProductCustomer)e.Item);
int currentIdx = e.ItemIndex;
if (currentIdx != -1)
{
if (currentIdx > _lastItemAppearedIdx)
{
if (_allGroups.Count == 0)
return;
if (currentIdx== _expandedGroups.Count-2)
{
//...
}
_lastItemAppearedIdx = currentIdx;
}
}
}