I'm new to Programming and have some difficulties with cascading ComboBox to TextBox. Hire is my code:
MainWindow.xaml
Window x:Class="WpfApplication26.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid Margin="0,0,0,-1">
<ComboBox x:Name="Category" HorizontalAlignment="Left" VerticalAlignment="Top" Width="120" SelectionChanged="Category_SelectionChanged" Margin="309,52,0,0">
<ListBoxItem Name="clComboBoxItem1" Content="Comedy" Height="25"/>
<ListBoxItem Name="clComboBoxItem2" Content="Drama" Height="25"/>
<ListBoxItem Name="clComboBoxItem3" Content="Science Fisction" Height="25"/>
</ComboBox>
<ComboBox x:Name="Shows" HorizontalAlignment="Left" VerticalAlignment="Top" Width="120" Margin="309,79,0,0" SelectionChanged="Shows_SelectionChanged" />
<TextBox x:Name="TextBox1" HorizontalAlignment="Left" Height="23" Margin="309,106,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
</Grid>
MainWindow.xamlcs
namespace WpfApplication26
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void Category_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
//Create List for Comedy selection
List<fruits> dropDownList_Comedy = new List<fruits>();
dropDownList_Comedy.Add(new fruits() { price = 10, Name = "Apples" });
dropDownList_Comedy.Add(new fruits() { price = 9, Name = "Bammamas" });
dropDownList_Comedy.Add(new fruits() { price = 1, Name = "Mango" });
//Create List for Drama selection
List<fruits> dropDownList_Drama = new List<fruits>();
dropDownList_Drama.Add(new fruits() { price = 10, Name = "Liver"});
//Create List for Science Fiction selection
List<fruits> dropDownList_SciFi = new List<fruits>();
dropDownList_SciFi.Add(new fruits() { price = 10, Name = "Apples2" });
//Check for SelectedIndex value and assign appropriate list to 2nd
if (Category.SelectedIndex == 0)
{
Shows.ItemsSource = dropDownList_Comedy;
Shows.DisplayMemberPath = "Name";
}
else if (Category.SelectedIndex == 1)
{
Shows.ItemsSource = dropDownList_Drama;
Shows.DisplayMemberPath = "Name";
}
else if (Category.SelectedIndex == 2)
{
Shows.ItemsSource = dropDownList_SciFi;
Shows.DisplayMemberPath = "Name";
}
{
}
}
private void Shows_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
{
fruits dropDownList_Comedy = Shows.SelectedItem as fruits ;
TextBox1.Text = Convert.ToString(dropDownList_Comedy.price);
}
{
fruits dropDownList_Drama = Shows.SelectedItem as fruits;
TextBox1.Text = Convert.ToString(dropDownList_Drama.price);
}
{
fruits dropDownList_SciFi = Shows.SelectedItem as fruits;
TextBox1.Text = Convert.ToString(dropDownList_SciFi.price);
}
}
}
}
Class1.cs
class fruits
{
public int price { get; set; }
public string Name { get; set; }
}
}
There is problem with System.NullReferenceException. I dont know what to do with it. Thanks for helping.
You're using SelectedValue instead of SelectedItem in your second block in the Shows_SelectionChanged function.
SelectedValue returns a String, which can't be parsed into a fruits (so it'll return null). And you're trying to access a member of null when using null.price, so it raises a NullReferenceException.
Edit
If you only want to display the SelectedItem of a ListBox in a TextBlock you can do:
<ListBox x:Name="MyListBox">
...
</ListBox>
<TextBox Text="{Binding ElementName=MyListBox,
Path=SelectedItem,
TargetNullValue=Nothing is selected,
Mode=OneWay}"/>
You don't need code behind in this case.
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