Develop Reference

I can't add an Entity Framework entry. System.ArgumentNullException: "The value cannot be null. Parameter name: entity"

There is a WPF form containing 8 textboxes.
<StackPanel Grid.Column="2">
<TextBox Margin="5" Width="100" Text="{Binding SelectedOrder.OrderCode}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.ClientID}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.RouteCode}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.DriverID}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.TCCode}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.Date}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.StartDate}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<TextBox Margin="10" Width="100" Text="{Binding SelectedOrder.EndDate}" FontSize="16" FontWeight="Normal" FontStyle="Normal"/>
<Button Margin="50" Width="100" Content="Create"
Command="{Binding AddCommand}"
/>
</StackPanel>
There is a ViewModel class that implements the transfer of data from the view to the model
public class OrderViewModel : INotifyPropertyChanged
{
private ObservableCollection<Order> orderList; //list of records in the Order table
private Order selectedOrder; // specific entry in Order
private TransportCompanyEntities transportCompanyEntities; // context?
public Order SelectedOrder
{
get { return selectedOrder; }
set
{
selectedOrder = value;
OnPropertyChanged(nameof(SelectedOrder));
}
}
public ObservableCollection<Order> OrderList
{
get { return orderList; }
set
{
orderList = value;
OnPropertyChanged(nameof(OrderList));
}
}
public OrderViewModel()
{
transportCompanyEntities = new TransportCompanyEntities();
Load Orders();
}
private void LoadOrders()
{
OrderList = new ObservableCollection<Order>(transportCompanyEntities.Order);
}
private RelayCommand addCommand;
public RelayCommand AddCommand
{
get
{
return addCommand ??
(addCommand = new RelayCommand(obj =>
{
transportCompanyEntities.Order.Add(SelectedOrder);
transportCompanyEntities.SaveChanges();
}));
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public class RelayCommand{}
When the button is clicked, an entry should be created, but an error occurs
How can i fix it?
System.ArgumentNullException: "Value cannot be null. Parameter name: entity"
I understand that I am trying to add an empty entry, but it is not clear to me why it is not created when the button is clicked.

Checkbox Event not trigerred in Listview UWP

I'm actually developping an UWP app who's reading Excel data, and display it on a form. Every Excel sheet are represented with RadioButton, and when the user click on a RadioButton, I update a ListView with the corresponding data.
Every item of the ListView have different data, and 2 checkboxes. This checkboxes can have the state "true" or "false", and if the user need to change the state, I want to modify his value
But the problem is, there is no event triggered with all the checkboxes when I check them. I tried to search and try to make my own template, but without success.
All the data are stored in a class :
public class REFERENCES
{
public int AI_ID { get; set; }
public int ID_poste { get; set; }
public string reference { get; set; }
public string designation { get; set; }
public bool avance { get; set; }
public bool jour { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
public REFERENCES(int ai_id, int id_poste, string ref_, string des_, string avance_, string jour_)
{
AI_ID = ai_id;
ID_poste = id_poste;
reference = ref_;
designation = des_;
if(jour_ != null)
{
jour = true;
}
else
{
jour = false;
}
if (avance_ != null)
{
avance = true;
}
else
{
avance = false;
}
}
public void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
And this is my ListView :
<ListView x:Name="ListViewData" SelectionMode="None" HorizontalAlignment="Center" Height="412" VerticalAlignment="Top" Width="650" Margin="0,218,0,0" >
<ListView.HeaderTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center" Height="35" Margin="0,0,0,0" VerticalAlignment="Center" >
<TextBlock Text="AI_ID" Width="0" Visibility="Collapsed" />
<TextBlock Text="Désignations" FontSize="20" Width="300" Foreground="Blue" TextAlignment="Center" VerticalAlignment="Center" />
<TextBlock Text="Références" FontSize="20" Width="150" Foreground="Blue" TextAlignment="Center" VerticalAlignment="Center" />
<TextBlock Text="Avance" FontSize="20" Width="100" Foreground="Blue" TextAlignment="Center" VerticalAlignment="Center" />
<TextBlock Text="Jour" FontSize="20" Width="100" Foreground="Blue" TextAlignment="Center" VerticalAlignment="Center" />
</StackPanel>
</DataTemplate>
</ListView.HeaderTemplate>
<ListView.ItemTemplate>
<DataTemplate x:DataType="ExcelLinkData:REFERENCES">
<StackPanel Orientation="Horizontal" >
<TextBlock Name="ItemAI_ID" Text="{x:Bind AI_ID}" Width="0" />
<TextBlock Name="ItemDesignation" Text="{x:Bind designation}" Width="300" FontSize="16" Height="55" VerticalAlignment="Center" HorizontalAlignment="Center" TextAlignment="Center"/>
<TextBlock Name="ItemReference" Text="{x:Bind reference}" Width="150" FontSize="16" Height="55" VerticalAlignment="Center" HorizontalAlignment="Center" TextAlignment="Center" />
<Grid Width="100" Height="55" VerticalAlignment="Center" HorizontalAlignment="Center">
<CheckBox Name="ItemAvance" IsChecked="{x:Bind avance}" Tag="{x:Bind AI_ID}" Checked="CHANGE_STATUS_REFERENCE"/>
</Grid>
<Grid Width="100" Height="55" VerticalAlignment="Center" HorizontalAlignment="Center">
<CheckBox Name="ItemJour" IsChecked="{x:Bind jour}" Tag="{x:Bind AI_ID}" Checked="CHANGE_STATUS_REFERENCE"/>
</Grid>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The method "CHANGE_STATUS_REFERENCE" is the method where I want to change the state in my class.
I tried different solutions, but I'm not an expert in UWP, so if anyone got an advice, I'll take it !
Thanks in advance for your time !
Guillaume

In UWP, default mode for Binding is OneTime. And when you change property from viewmodel then no event is triggered. By changing Binding to OneWay / TwoWay (depending on your usage), viewmodel will trigger the event.
Change
IsChecked="{x:Bind jour}"
To
IsChecked="{x:Bind jour Mode=TwoWay}"

Change
<CheckBox Name="ItemAvance" IsChecked="{x:Bind avance}" Tag="{x:Bind AI_ID}" Checked="CHANGE_STATUS_REFERENCE"/>
to
<CheckBox Name="ItemAvance" IsChecked="{x:Bind avance}" Tag="{x:Bind AI_ID}" Command="{Binding CHANGE_STATUS_REFERENCE}"/>
Add a "Flip Function" to your class:
private void Flip()
{
this.avance = !this.avance;
}
Set up a RelayCommand:
RelayCommand _flipCommand = new RelayCommand(this.Flip);
and Implement CHANGE_STATUS_REFERENCE as an ICommand like so:
public ICommand CHANGE_STATUS_REFERENCE
{
get
{
return _flipCommand;
}
}

display grid item position number in a grid observable collection

Below is my item template in a grid view.
</Grid.ColumnDefinitions>
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding SerialNumber}" VerticalAlignment="Center" HorizontalAlignment="Left" FontWeight="Bold" Margin="10" FontSize="25"/>
<TextBlock Text="." VerticalAlignment="Center" HorizontalAlignment="Left" FontWeight="Bold" FontSize="25" />
</StackPanel>
<Image Grid.Column="0" Margin="20" Height="100" Width="150" HorizontalAlignment="Center" Source="{Binding ImageUri,Mode=TwoWay}" VerticalAlignment="Center"/>
</StackPanel>
</Border>
</DataTemplate>
</GridView.ItemTemplate>
what i am trying to achieve is to display the item position in the collection in the TextBlock Text="{Binding SerialNumber} (if this were to be a list view, it would be row number), please how do i achieve this.

You just need to define a class with the specific properties and bind it on xaml.
I made a simple code sample for your reference:
<GridView ItemsSource="{Binding oc}">
<GridView.ItemTemplate>
<DataTemplate>
<Border>
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding SerialNumber}" VerticalAlignment="Center" HorizontalAlignment="Left" FontWeight="Bold" Margin="10" FontSize="25"/>
<TextBlock Text="." VerticalAlignment="Center" HorizontalAlignment="Left" FontWeight="Bold" FontSize="25" />
</StackPanel>
<Image Grid.Column="0" Margin="20" Height="100" Width="150" HorizontalAlignment="Center" Source="{Binding source,Mode=TwoWay}" VerticalAlignment="Center"/>
</StackPanel>
</Border>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
public sealed partial class MainPage : Page
{
public ObservableCollection<Test> oc { get; set;}
public MainPage()
{
this.InitializeComponent();
oc = new ObservableCollection<Test>();
oc.CollectionChanged += Oc_CollectionChanged;
for (int i=0;i<10;i++)
{
oc.Add(new Test() {SerialNumber=i,source=new BitmapImage(new Uri("ms-appx:///Assets/test.png")) });
}
this.DataContext = this;
}
private void Oc_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
{
for (int i =e.OldStartingIndex; i<oc.Count;i++)
{
oc[i].SerialNumber = i;
}
}
}
}
public class Test:INotifyPropertyChanged
{
private int _SerialNumber;
public int SerialNumber
{
get { return _SerialNumber; }
set
{
_SerialNumber = value;
RaisePropertyChanged("SerialNumber");
}
}
private BitmapImage _source;
public BitmapImage source
{
get { return _source; }
set
{
_source = value;
RaisePropertyChanged("source");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string PropertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this,new PropertyChangedEventArgs(PropertyName));
}
}
}

WPF MVVM Clear textbox bound to Listview SelectedItem

I am trying to learn about C# mvvm and wpf, so i decided to make a simple project(a book&readers managing application for a library) and now i am a little lost so i would really appreciate some help.
In my view i have a listview displaying the readers, and a bunch of textboxes bound to the selected item of the listview(name, adress,etc).
The listview is bound to an observable collection of readers created from a database table(Readers) with Linq2SQL.
Below the textboxes i have a few buttons (Clear/Add/Save/Delete).
The problems i am having are that the "selected item" of the listview, seems null if i try to execute some commands when i click the buttons.
when i click the clear button, if i have a breakpoint on the selected item(reader), it shows that it gets null/empty spaced, but the textboxes dont clear;
If in the Clear method in use the SelectedReader property, and assign empty spaces to its attributes, the selected item in the listview also clears(because its bound to Reader's FullName property)
i have other problems on adding a new reader, and saving changes, and i assume its because of wrong linq queries but i hope i can fix the current ones and move on afterwards.
What should i do?
ViewModel
public class MainWindowViewModel : ViewModelBase
{
private Reader selectedReader;
private ObservableCollection<Reader> readerList;
public MainWindowViewModel()
{
SelectedReader = new Reader()
{
FullName = "",
SerialNumber = "",
IdNumber = "",
Adress = "",
AltContactMethods = ""
};
BookDBDataContext rdb = new BookDBDataContext();
ReadersList = new ObservableCollection<Reader>(rdb.Readers);
AddR = new TblQryCommand(AddToDb);
EditR = new TblQryCommand(EditToDb);
DeleteR = new TblQryCommand(DeleteFromDb);
ClearR = new TblQryCommand(ClearReaderFields);
}
public TblQryCommand AddR { get; private set; }
public TblQryCommand EditR { get; private set; }
public TblQryCommand DeleteR { get; private set; }
public TblQryCommand ClearR { get; private set; }
//Reader List
public ObservableCollection<Reader> ReadersList
{
get { return readerList; }
set
{
if (readerList != value)
{
readerList = value;
RaisePropertyChanged();
}
}
}
public Reader SelectedReader
{
get { return selectedReader; }
set
{
if (selectedReader != value)
{
selectedReader = value;
RaisePropertyChanged();
}
}
}
public void AddToDb()
{
BookDBDataContext db = new BookDBDataContext();
Reader r = new Reader
{
FullName = SelectedReader.FullName,
SerialNumber = SelectedReader.SerialNumber,
IdNumber = SelectedReader.IdNumber,
Adress = SelectedReader.Adress,
AltContactMethods = SelectedReader.AltContactMethods
};
db.Readers.InsertOnSubmit(r);
db.Readers.Context.SubmitChanges();
}
public void DeleteFromDb()
{
}
public void EditToDb()
{
}
public void ClearReaderFields()
{
SelectedReader = new Reader
{
Id = 0,
FullName = string.Empty,
SerialNumber = string.Empty,
IdNumber = string.Empty,
Adress = string.Empty,
AltContactMethods = string.Empty
};
}
View:
<ListView Name="listviewReaders" ItemsSource="{Binding ReadersList}" SelectedItem="{Binding SelectedReader,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Width="140" Height="180" Margin="10,68,492,281">
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding FullName}" />
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<TextBox x:Name="txtBxFullName" HorizontalAlignment="Left" Height="22" Margin="211,68,0,0" TextWrapping="Wrap" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.FullName, Mode=TwoWay, UpdateSourceTrigger=Explicit}" VerticalAlignment="Top" Width="315"/>
<TextBox x:Name="txtBxSerialNumber" HorizontalAlignment="Left" Height="22" Margin="211,95,0,0" TextWrapping="Wrap" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.SerialNumber, Mode=TwoWay, UpdateSourceTrigger=Explicit}" VerticalAlignment="Top" Width="315"/>
<TextBox x:Name="txtBxIdNumber" HorizontalAlignment="Left" Height="22" Margin="211,122,0,0" TextWrapping="Wrap" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.IdNumber, Mode=TwoWay, UpdateSourceTrigger=Explicit}" VerticalAlignment="Top" Width="315"/>
<TextBox x:Name="txtBxAdress" HorizontalAlignment="Left" Height="22" Margin="211,149,0,0" TextWrapping="Wrap" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.Adress, Mode=TwoWay, UpdateSourceTrigger=Explicit}" VerticalAlignment="Top" Width="315"/>
<TextBox x:Name="txtBxAltContactMethods" HorizontalAlignment="Left" Height="22" Margin="211,176,0,0" TextWrapping="Wrap" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.AltContactMethods, Mode=TwoWay, UpdateSourceTrigger=Explicit}" VerticalAlignment="Top" Width="315"/>
<Button x:Name="btnReader_Clear" Content="Clear" Command="{Binding ClearR}" HorizontalAlignment="Left" Margin="211,228,0,0" VerticalAlignment="Top" Width="75"/>
<Button x:Name="btnReader_Save" Content="Save" Command="{Binding EditR}" HorizontalAlignment="Left" Margin="291,228,0,0" VerticalAlignment="Top" Width="75"/>
<Button x:Name="btnReader_Add" Content="Add New" Command="{Binding AddR}" HorizontalAlignment="Left" Margin="371,228,0,0" VerticalAlignment="Top" Width="75"/>
<Button x:Name="btnReader_Delete" Content="Delete" Command="{Binding DeleteR}" HorizontalAlignment="Left" Margin="451,228,0,0" VerticalAlignment="Top" Width="75"/>

Have you tried to set the Binding of the Text-Property of your textboxes to your ViewModel's SelectedReader-Property directly?
So instead of writing this:
<TextBox x:Name="txtBxFullName" Text="{Binding ElementName=listviewReaders, Path=SelectedItem.FullName, Mode=TwoWay, UpdateSourceTrigger=Explicit}" ... />
you would write:
<TextBox x:Name="txtBxFullName" Text="{Binding Path=SelectedReader.FullName, Mode=TwoWay, UpdateSourceTrigger=Explicit}" ... />

C# ListBox, different background for each item

I have ListBox in xaml:
<ListBox Name="feedListBox" Height="758" HorizontalAlignment="Center" Margin="0,10,0,0" VerticalAlignment="Top" Width="480" ScrollViewer.VerticalScrollBarVisibility="Auto" SelectionChanged="feedListBox_SelectionChanged" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="1" Background="White">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel VerticalAlignment="Top" Width="480">
<TextBlock FontWeight="Bold" FontSize="24" Name="feedTitle" TextWrapping="Wrap" Margin="12,0,0,0" HorizontalAlignment="Left" Foreground="#FF000000" Text="{Binding Title.Text, Converter={StaticResource RssTextTrimmer}}" />
<TextBlock Name="feedSummary" Foreground="#FF000000" TextWrapping="Wrap" Margin="12,0,0,0" Text="{Binding Summary.Text, Converter={StaticResource RssTextTrimmer}}" />
<TextBlock Name="feedPubDate" Foreground="#FF939393" Margin="12,0,10,10" Text="{Binding PublishDate.DateTime}" HorizontalAlignment="Right" />
<Border BorderThickness="1" Height="2" HorizontalAlignment="Center" VerticalAlignment="Top" Width="480" BorderBrush="Black" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
How can I specify different background for each item?

add a Brush property to your viewmodel and bind the controls in your DataTemplate to it
ViewModel:
using System.ComponentModel;
using System.Windows.Media;
...
public class YourViewModel : INotifyPropertyChanged{
...
private Brush _backgroundCol = Brushes.Red; //Default color
public Brush BackgroundCol
{
get { return _backgroundCol; }
set
{
_backgroundCol = value;
OnPropertyChanged("BackgroundCol");
}
}
...
}
xaml:
<TextBlock Name="feedPubDate" Background="{Binding Path=BackgroundCol}" />
for Information about how to implement the INotifyPropertyChanged interface have a look at: Implementing INotifyPropertyChanged - does a better way exist?

Try this:
XAML:
<ListBox Name="feedListBox" Height="758" HorizontalAlignment="Center" Margin="0,10,0,0" VerticalAlignment="Top" Width="480" ScrollViewer.VerticalScrollBarVisibility="Auto" SelectionChanged="feedListBox_SelectionChanged" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="1" Background="White">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel VerticalAlignment="Top" Width="480">
<Grid Background="{Binding feedTitleBack}">
<TextBlock FontWeight="Bold" FontSize="24" Name="feedTitle" TextWrapping="Wrap" Margin="12,0,0,0" HorizontalAlignment="Left" Foreground="#FF000000" Text="{Binding Title}"/>
</Grid>
<Grid Background="{Binding feedSummaryBack}">
<TextBlock Name="feedSummary" Foreground="#FF000000" TextWrapping="Wrap" Margin="12,0,0,0" Text="{Binding Summary}" />
</Grid>
<Grid Background="{Binding feedPubDateBack}">
<TextBlock Name="feedPubDate" Foreground="#FF939393" Margin="12,0,10,10" Text="{Binding PublishDate}" HorizontalAlignment="Right" />
</Grid>
<Border BorderThickness="1" Height="2" HorizontalAlignment="Center" VerticalAlignment="Top" Width="480" BorderBrush="Black" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
CS:
public class data
{
public string Title { get; set; }
public string feedTitleBack { get; set; }
public string Summary { get; set; }
public string feedSummaryBack { get; set; }
public string PublishDate { get; set; }
public string feedPubDateBack { get; set; }
public data() { }
public data(string Title, string feedTitleBack, string Summary, string feedSummaryBack, string PublishDate, string feedPubDateBack)
{
this.Title = Title;
this.feedTitleBack = feedTitleBack;
this.Summary = Summary;
this.feedSummaryBack = feedSummaryBack;
this.PublishDate = PublishDate;
this.feedPubDateBack = feedPubDateBack;
}
}
void loadData()
{
List<data> obj = new List<data>();
obj.Add(new data("Title1", "Red", "Summary1", "Green", "Date", "Blue"));
obj.Add(new data("Title1", "#DD4B39", "Summary1", "#006621", "Date", "#1A0DAB"));
feedListBox.ItemsSource = obj;
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
loadData();
}