System.FormatException on Content.View-Initialization

Question

I'm developing an app for my Bachelor's degree for creating and managing archaeological Field Guides. One functionality should enable the user to create new Field Guides in-app. A Field guide should consist of general infos (title, author, etc.) and multiple entries for artifact-types. I want to realize that by having one ContentPage with two views - one for the book-info, one for a list of entries. The user should be able to switch between the two views. To achieve that I created both as ContentViews, included them into the Parent-XAML and bound their IsVisible-attributes to individual booleans in the ViewModel. Strangely "NewBookInfo" throws an exeption on initialization, while "NewBookEntryList" works just fine. I couldn't find a solution on google and am kinda grasping at straws right now...

<ColumnDefinition Width="100/3*" /> results in runtime exception in InitializeComponent():

System.FormatException
Message=One of the identified items was in an invalid format.
Source=Xamarin.Forms.Core
StackTrace:
 at Xamarin.Forms.GridLengthTypeConverter.ConvertFromInvariantString(String value)
 ...

My Parent-Page:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"     
             xmlns:local="clr-namespace:FieldGuide.Views"
             x:Class="FieldGuide.AddBook">

    <StackLayout Spacing="1" VerticalOptions="Fill">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition Width="Auto" />

            </Grid.ColumnDefinitions>
            <Label Text="New Guide" FontAttributes="Bold" FontSize="30" 
                   HorizontalOptions="Center"
                   VerticalOptions="CenterAndExpand"
                   Grid.Row="0" Grid.Column="0" />
            <ImageButton Source="Return_klein.png" Grid.Row="0" Grid.Column="1" Command="{Binding ReturnCommand}"/>
            <ImageButton Source="Hamburger_Icon_klein.png" Grid.Row="0" Grid.Column="2" Command="{Binding MenuCommand}"/>
        </Grid>
        <!--BackgroundColor="Transparent" bei Buttons einfügen-->
        <local:NewBookInfo VerticalOptions="FillAndExpand" IsVisible="{Binding BookInfoVisible}"/>
        <local:NewBookEntryList VerticalOptions="FillAndExpand" IsVisible="{Binding BookEntriesVisible}"/>
    </StackLayout>

</ContentPage>

NewBookInfo.xaml

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="FieldGuide.Views.NewBookInfo">
  <ContentView.Content>
        <StackLayout>
            <Grid Margin="10, 10">
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto"/>
                    <RowDefinition Height="Auto"/>
                    <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="30*"/>
                    <ColumnDefinition Width="70*"/>
                </Grid.ColumnDefinitions>
                <Label Text="Title" FontSize="20" 
                   HorizontalOptions="Center" VerticalOptions="CenterAndExpand" 
                   Grid.Row="0" Grid.Column="0"/>
                <Label Text="Author" FontSize="20" 
                   HorizontalOptions="Center" VerticalOptions="CenterAndExpand" 
                   Grid.Row="1" Grid.Column="0"/>
                <Label Text="Tags" FontSize="20" 
                   HorizontalOptions="Center" VerticalOptions="CenterAndExpand" 
                   Grid.Row="2" Grid.Column="0"/>
                <Entry Grid.Row="0" Grid.Column="1"/>
                <Entry Grid.Row="1" Grid.Column="1"/>
                <Entry Placeholder="Separate with Comma" Grid.Row="2" Grid.Column="1"/>
            </Grid>
            <Grid VerticalOptions="EndAndExpand" Margin="10, 10">
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="100/3*"/>
                    <ColumnDefinition Width="100/3*"/>
                    <ColumnDefinition Width="100/3*"/>
                </Grid.ColumnDefinitions>
                <Button Text="Save" Grid.Row="0" Grid.Column="0" 
                        Command="{Binding SaveBook}"/>
                <Button Text="Entries" Grid.Row="0" Grid.Column="1" 
                        Command="{Binding NewEntry}"/>
                <Button Text="Discard" Grid.Row="0" Grid.Column="2" 
                        Command="{Binding DiscardBook}"/>
            </Grid>
        </StackLayout>
    </ContentView.Content>
</ContentView>

For comparison NewBookEntryList.xaml (ListView is not yet finished)

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="FieldGuide.Views.NewBookEntryList">
    <ContentView.Content>
        <StackLayout>
            <ListView x:Name="FileSystem" ItemsSource="{Binding Entries}" SelectedItem="{Binding SelectedEntry}" VerticalOptions="FillAndExpand">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>

                                <Label Text="{Binding Name}" Margin="10" FontSize="Medium" VerticalOptions="Center" HorizontalOptions="StartAndExpand"/>
                            </Grid>
                        </ViewCell>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
            <Grid VerticalOptions="EndAndExpand" Margin="10, 10">
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="50*"/>
                    <ColumnDefinition Width="50*"/>
                </Grid.ColumnDefinitions>
                <Button Text="Book Info" Grid.Row="0" Grid.Column="0" 
                        Command="{Binding SaveBook}"/>
                <Button Text="New Entry" Grid.Row="0" Grid.Column="1" 
                        Command="{Binding NewEntry}"/>
            </Grid>
        </StackLayout>
    </ContentView.Content>
</ContentView>

This is how I wish it to be in the end.

Answer 1

The problem was in the width-declaration of the last grid in NewBookInfo.xaml.But the error wasn't flagged by the built-in error-detection in VS. Instead of

<ColumnDefinition Width="100/3*"/>

I just replaced it with

<ColumnDefinition Width="33*"/>

Thanks to @Jason, for providing help in the comments.