Xamarin.Forms. How to call methods of xaml element created from item source in code behind?

Issue

How can i call InvalidateSurface method in this case? This method does not refer to the bindable object, but to the xaml element itself. I'm new to app development and I really need to figure this out.

Part of my xaml file

<StackLayout>
        <ListView
        CachingStrategy="RecycleElement"
        HasUnevenRows="True"
        ItemsSource="{Binding TheoryContentList}"
        SelectionMode="None"
        SeparatorVisibility="None"
        x:Name="listView">
            <ListView.ItemTemplate>
                <DataTemplate x:DataType="model:Wrapper">
                    <ViewCell>
                        <StackLayout>
                            <ScrollView>
                                <math:TextView x:Name="textView" LaTeX="{Binding Formula}" FontSize="{Binding Source={x:Reference TheoryPage1},Path=BindingContext.FSize}" HeightRequest="{Binding HeightReq}"/>
                            </ScrollView>
                            <Label LineBreakMode="WordWrap" HeightRequest="{Binding LabelHeightReq}" HorizontalTextAlignment="End" Margin="15, 0">
                                <Label.FormattedText>
                                    <FormattedString>
                                        <Span Text="{Binding BoldText}" FontAttributes="Bold"/>
                                        <Span Text="{Binding Text1}" FontSize="Small" FontAttributes="Italic"/>
                                        <Span x:Name="{Binding }" Text="{Binding Link.Text}" FontSize="Small" TextDecorations="Underline" FontAttributes="Italic" TextColor="Blue">
                                            <Span.GestureRecognizers>
                                                <TapGestureRecognizer Command="{Binding Source={x:Reference TheoryPage1},Path=BindingContext.LinkTappedCommand}" CommandParameter="{Binding Link}"/>
                                            </Span.GestureRecognizers>
                                        </Span>
                                        <Span Text="{Binding Text2}"/>
                                    </FormattedString>
                                </Label.FormattedText>
                            </Label>
                        </StackLayout>
                    </ViewCell>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
        <Label x:Name="linkLabel" FontSize="Small" TextColor="Gray" Padding="0" Margin="15,0" HorizontalTextAlignment="Start"/>
    </StackLayout>

My code behind

public TheoryPage()
{
    InitializeComponent();
    BindingContext = _viewModel = new TheoryViewModel();
    textView.InvaludateSurface();
}

Solution

To solve this problem i used a wrapper class:

public class MyTextView : TextView
{
    public MyTextView()
    {
        InvalidateSurface();
    }
}

And used this class in xaml file:

<views:MyTextView x:Name="textView" LaTeX="{Binding Formula}" Margin="15, 5"/>

Answered By - Андрей Ерзунов