Serialization Json C#

Question

I have WPF project "LittleLibrary" and and it must enable adding and deleting books. So in Xaml i have form and one button

Here is how it looks like https://imgur.com/1N7PYWm

and in C# code i'm trying to serialization like this (I'm using Newtonsoft.Json)

public class Book
{
  public string Title { get; set; }
  public string Author { get; set; }
  public string Genre { get; set; }
  public int Year { get; set; }
  public string Cover { get; set; }
  public int Availability { get; set; }
  public string Description { get; set; }
}
public class RootObject
{
    public List<Book> Book { get; set; }
}   
private void btnAdd_Click(object sender, RoutedEventArgs e)
{
     RootObject rootObjectSerializacja = new RootObject();

     Book newBook = new Book();
     newBook.Title = titleTextBox.Text;
     newBook.Author = authorTextBox.Text;
     newBook.Genre = gatunekTextBox.Text;
     newBook.Year = int.Parse(rokWydaniaTextBox.Text);
     newBook.Cover = okladkaTextBox.Text;
     newBook.Availability = int.Parse(dostepnoscTextBox.Text);
     newBook.Description = opisTextBox.Text;

     rootObjectSerializacja.Book.Add(newBook);


        string content = JsonConvert.SerializeObject(rootObjectSerializacja);

        File.WriteAllText("newJsonFile.json", content);
    }

Code from my Xaml :

<Grid>

    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" MinWidth="200"></ColumnDefinition>
        <ColumnDefinition Width="*" MinWidth="300"></ColumnDefinition>
    </Grid.ColumnDefinitions>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="7*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>

        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"></ColumnDefinition>
                <ColumnDefinition Width="*"></ColumnDefinition>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
                <RowDefinition></RowDefinition>
            </Grid.RowDefinitions>
            <!--Lewa strona -->
            <Label x:Name="titleLabel" Grid.Column="0" Grid.Row="0" HorizontalAlignment="Right" VerticalAlignment="Center">Title:</Label>
            <TextBox x:Name="titleTextBox" Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Center" Width="150"></TextBox>
            <Label x:Name="authorLabel" Grid.Column="0" Grid.Row="1" HorizontalAlignment="Right" VerticalAlignment="Center">Author:</Label>
            <TextBox x:Name="authorTextBox" Grid.Column="1" Grid.Row="1" HorizontalAlignment="Center" VerticalAlignment="Center" Width="150"></TextBox>
            <Label x:Name="gatunekLabel" Grid.Column="0" Grid.Row="2" HorizontalAlignment="Right" VerticalAlignment="Center">Gentre:</Label>
            <TextBox x:Name="gatunekTextBox" Grid.Column="1" Grid.Row="2" Width="150" HorizontalAlignment="Center" VerticalAlignment="Center" ></TextBox>
            <Label x:Name="rokLabel" Grid.Column="0" Grid.Row="3" HorizontalAlignment="Right" VerticalAlignment="Center">Year:</Label>
            <TextBox x:Name="rokWydaniaTextBox" Grid.Column="1" Grid.Row="3" Width="150" HorizontalAlignment="Center" VerticalAlignment="Center" ></TextBox>
            <Label x:Name="okladkaLabel" Grid.Column="0" Grid.Row="4" HorizontalAlignment="Right" VerticalAlignment="Center">Cover:</Label>
            <TextBox x:Name="okladkaTextBox" Grid.Column="1" Grid.Row="4" Width="150" HorizontalAlignment="Center" VerticalAlignment="Center" ></TextBox>
            <Label x:Name="dostepnoscLabel" Grid.Column="0" Grid.Row="5" HorizontalAlignment="Right" VerticalAlignment="Center">Avb:</Label>
            <TextBox x:Name="dostepnoscTextBox" Grid.Column="1" Grid.Row="5" Width="150" HorizontalAlignment="Center" VerticalAlignment="Center" ></TextBox>
            <Label x:Name="opisLabel" Grid.Column="0" Grid.Row="6" HorizontalAlignment="Right" VerticalAlignment="Center">Description:</Label>
            <TextBox x:Name="opisTextBox" Grid.Column="1" Grid.Row="6" Width="150"  ></TextBox>

        </Grid>
        <Button x:Name="btnAdd" Grid.Column="0" Grid.Row="2" HorizontalAlignment="Center" VerticalAlignment="Center" Width="150" Margin="10" Click="btnAdd_Click" >ADD</Button>
    </Grid>

</Grid>

The problem is i have an Exception {"The object reference has not been set to the instance of the object."} System.NullReferenceException

And content is NULL. What i'm doing wrong ?

Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Selvin, Mar 18 '19 at 12:46
obviously list is null ... please learn how to read exceptions and use debugger ... — Selvin, Mar 18 '19 at 12:48

score 1 · Accepted Answer · edited Mar 18 '19 at 13:17

1

Try adding a constructor in your RootObject class.

public class RootObject
{
    public List<Book> Book { get; set; }

    public RootObject()
    {
       Book = new List<string>();
    }
}

edited Mar 18 '19 at 13:17

er-sho

8,871
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answered Mar 18 '19 at 12:51

Ian

122
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Serialization Json C#

1 Answers1