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CollectinView Grouping doesnt show all Items in the last Group

im working on an Mobile App for Android in Xamarin Forms, and have one problem. I have a ObservableCollection that i fill with the following Model.
private int _category_ID;
public int Category_ID
{
get
{
return _category_ID;
}
set
{
_category_ID = value;
OnPropertyChanged("_category_ID");
}
}
private string _category_Name;
public string Category_Name
{
get
{
return _category_Name;
}
set
{
_category_Name = value;
OnPropertyChanged("_category_Name");
}
}
private string _category_Description;
public string Category_Description
{
get
{
return _category_Description;
}
set
{
_category_Description = value;
OnPropertyChanged("_category_Description");
}
}
public CategoryModel(string name, List<ProductModel> products) : base(products)
{
Category_Name = name;
}
That works fine and all Categorys and Items shows right when i Debugging in the ObservableCollection. Example: Categroy 1 = 2 Items Category 2 = 3 Items Category 3 = 4 Items.
That works.
But my problem is, that when i use a CollectionView like this
<CollectionView ItemsSource="{Binding ObservCollectionCategory}" IsGrouped="True">
<CollectionView.ItemTemplate>
<DataTemplate>
<ScrollView>
<Grid Padding="10">
<StackLayout BackgroundColor="Blue">
<Label Text="{Binding Product_Name}"/>
<Label Text="{Binding Product_Description}"/>
</StackLayout>
</Grid>
</ScrollView>
</DataTemplate>
</CollectionView.ItemTemplate>
<CollectionView.GroupHeaderTemplate>
<DataTemplate >
<Label Text="{Binding Category_Name}"/>
</DataTemplate>
</CollectionView.GroupHeaderTemplate>
</CollectionView>
The View shows me only the first item of the last categroy and the other ignores. All other Categorys shows right.
When i create a blank Categroy at the end of the ObservableCollection then all Items, from the last category, shows in the View. But i have an empty Group then at the end.
I have try to show me the count in the header, and the count the right one (4).

You could try the code below.
Model:
public class ProductModel : INotifyPropertyChanged
{
private string _product_Name;
public string Product_Name
{
get
{
return _product_Name;
}
set
{
_product_Name = value;
OnPropertyChanged("Product_Name");
}
}
private string _product_Description;
public string Product_Description
{
get
{
return _product_Description;
}
set
{
_product_Description = value;
OnPropertyChanged("Product_Description");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public class CategoryModel : List<ProductModel>, INotifyPropertyChanged
{
private string _category_Name;
public event PropertyChangedEventHandler PropertyChanged;
public string Category_Name
{
get
{
return _category_Name;
}
set
{
_category_Name = value;
OnPropertyChanged("Category_Name");
}
}
public CategoryModel(string name, List<ProductModel> diary) : base(diary)
{
Category_Name = name;
}
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Code behind:
public ObservableCollection<CategoryModel> ObservCollectionCategory { get; set; } = new ObservableCollection<CategoryModel>();
public Page18()
{
InitializeComponent();
ObservCollectionCategory.Add(new CategoryModel("Categroy 1", new List<ProductModel>
{
new ProductModel(){ Product_Name="item1", Product_Description="Description1"},
new ProductModel(){ Product_Name="item2", Product_Description="Description2"},
}));
ObservCollectionCategory.Add(new CategoryModel("Categroy 2", new List<ProductModel>
{
new ProductModel(){ Product_Name="item1", Product_Description="Description1"},
new ProductModel(){ Product_Name="item2", Product_Description="Description2"},
new ProductModel(){ Product_Name="item3", Product_Description="Description3"},
}));
ObservCollectionCategory.Add(new CategoryModel("Categroy 3", new List<ProductModel>
{
new ProductModel(){ Product_Name="item1", Product_Description="Description1"},
new ProductModel(){ Product_Name="item2", Product_Description="Description2"},
new ProductModel(){ Product_Name="item3", Product_Description="Description3"},
new ProductModel(){ Product_Name="item4", Product_Description="Description4"},
}));
this.BindingContext = this;
}
Output:

Property changed event is not getting fired wpf

I have to change the value in a text box dynamically, on selecting a value from a combox box, which is present in different view. when changing the dependency property's source, the propertychangedEventHandler value is not changing, i.e it is remaining as null, so the event is not getting fired. As a result the text in the textbox is not changing. Below is the code. I have bound the text in textbox to _name property.
public partial class Details : UserControl, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public string name = "";
public Details()
{
InitializeComponent();
Name = Connector.Name;
DataContext = this;
}
public string Name
{
get { return name; }
set
{
name = value; OnPropertyChanged("Name");
}
}
protected void OnPropertyChanged(string s)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(s));
}
}
}
Xaml code
<StackPanel Orientation="Vertical">
<TextBlock Text="Student Details" VerticalAlignment="Top" HorizontalAlignment="Center" FontSize="16" FontWeight="Bold"> </TextBlock>
<StackPanel Margin="0,5" Orientation="Horizontal" >
<Label MinWidth="100" MaxWidth="110">Name:</Label>
<Border BorderBrush="Gray" BorderThickness="2">
<TextBox Name="nametextbox" Text="{Binding Name,Mode=TwoWay}" Width="auto" MinWidth="100" FontWeight="Black"></TextBox>
</Border>
</StackPanel>

Is it possible that you accidentally exchanged name and _name, using name in XAML for the binding?
Usually you have a public property with a capitalized name, and a private field with a non-capitalized name, optionally prefixed with an underscore as you did.
So, you should have
public string Name {
get { return _name; }
set { _name = value; OnPropertyChanged("Name"); }
{
private string _name = "";
Please check the following:
If you're not currently binding to name instead of _name;
Either if that is or is not the case, please fix your naming convention, because it is a source of errors, and every example you'll find follow the convention I included above.

In your XAML, you are binding "Name" property and in your code, you have created _name property. So, you need to change it to "Name" property in your code.
Just change your property as per below:
private string _name = "";
public string Name
{
get { return _name; }
set {
_name = value;
OnPropertyChanged("Name");
}
}
Try this and let me know.

I have used eventaggregator for this purpose, as we need to change the text in the text box dynamically when an event in a different view is fired. Below is the C# code of both the DropView(where we select student name from a list), and DetailsView(where we display the details). I publish events in Drop.xaml.cs and subscribe to those events in Details.xaml.cs
Drop.xaml.cs
public partial class Drop : UserControl
{
private IEventAggregator iEventAggregator;
public Drop(IEventAggregator ieventaggregator)
{
InitializeComponent();
iEventAggregator = ieventaggregator;
this.DataContext = this;
var doc = XDocument.Load("C:\\Users\\srinivasaarudra.k\\Desktop\\students.xml");
var names = doc.Descendants("Name");
foreach (var item in names)
{
droplist.Items.Add(item.Value);
}
}
public string name;
public string Naam
{
get { return name; }
set { name = value;
iEventAggregator.GetEvent<Itemselectedevent>().Publish(Naam);
}
}
public string grade;
public string Grade
{
get { return grade; }
set
{
grade = value;
iEventAggregator.GetEvent<gradeevent>().Publish(Grade);
}
}
public string dept;
public string Dept
{
get { return dept; }
set
{
dept = value;
iEventAggregator.GetEvent<deptevent>().Publish(Dept);
}
}
public static string str;
public static string Str
{
get { return str; }
set {
str = value;
}
}
private void droplist_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var sel = droplist.SelectedValue;
Str=sel.ToString();
XmlDocument doc2 = new XmlDocument();
doc2.Load("C:\\Users\\srinivasaarudra.k\\Desktop\\students.xml");
var details = doc2.DocumentElement.SelectNodes("/Students/StudentDetails");
foreach (XmlNode node in details)
{
if (node.SelectSingleNode("Name").InnerText == Str)
{
Naam = node.SelectSingleNode("Name").InnerText;
Grade = node.SelectSingleNode("Grade").InnerText;
Dept = node.SelectSingleNode("Department").InnerText;
}
}
// Details det = new Details();
Details dt = new Details(iEventAggregator);
}
}
public class Itemselectedevent:Prism.Events.PubSubEvent<string>
{
}
public class gradeevent : Prism.Events.PubSubEvent<string>
{
}
public class deptevent : Prism.Events.PubSubEvent<string>
{
}
Details.xaml.cs
public partial class Details : UserControl,INotifyPropertyChanged
{
public IEventAggregator iEventAggregator;
public event PropertyChangedEventHandler PropertyChanged;
public static string name;
public static string dept;
public static string grade;
[Bindable(true)]
public string Naam
{
get { return name; }
set
{
name = value;
OnPropertyChanged("Naam");
}
}
[Bindable(true)]
public string Grade
{
get { return grade; }
set
{
grade = value; OnPropertyChanged("Grade");
}
}
[Bindable(true)]
public string Dept
{
get { return dept; }
set
{
dept = value;
OnPropertyChanged("Dept");
}
}
public Details(IEventAggregator eventaggregator)
{
InitializeComponent();
this.iEventAggregator = eventaggregator;
iEventAggregator.GetEvent<Itemselectedevent>().Subscribe((str) => { Naam = str; });
iEventAggregator.GetEvent<gradeevent>().Subscribe((str) => { Grade = str; });
iEventAggregator.GetEvent<deptevent>().Subscribe((str) => { Dept = str; });
this.DataContext = this;
}
protected void OnPropertyChanged(string s)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(s));
}
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
Application.Current.Shutdown();
}
}

WPF Binding ComboBox to my ViewModel

I am trying to bind my ViewModel to my ComboBox. I have ViewModel class defined like this:
class ViewModel
{
public ViewModel()
{
this.Car= "VW";
}
public string Car{ get; set; }
}
I set this ViewModel as DataContext in Window_Load like:
private void Window_Loaded(object sender, RoutedEventArgs e)
{
this.DataContext = new CarModel();
}
Then in my xaml, I do this to bind my ComboBox to this ViewModel. I want to show the "VW" as selected by default in my ComboBox:
<ComboBox Name="cbCar" SelectedItem="{Binding Car, UpdateSourceTrigger=PropertyChanged}">
<ComboBoxItem Tag="Mazda">Mazda</ComboBoxItem>
<ComboBoxItem Tag="VW">VW</ComboBoxItem>
<ComboBoxItem Tag="Audi">Audi</ComboBoxItem>
</ComboBox>
I have 2 questions:
How do I set default value selected in Combo Box to "VW" (once form loads, it should show "VW" in combo box).
Instead of setting ComboBoxItems like above in xaml, how to I set it in my ViewModel and then load these in ComboBox?
Thanks,
UPDATE:
So far, I manage to implement this but I get error as below in the ViewModel c-tor:
namespace MyData
{
class ViewModel
{
public ViewModel()
{
this.Make = "";
this.Year = 1;
this.DefaultCar = "VW"; //this is where I get error 'No string allowed'
}
public IEnumerable<Car> Cars
{
get
{
var cars = new Car[] { new Car{Model="Mazda"}, new Car{Model="VW"}, new Car{Model="Audi"} };
DefaultCar = cars.FirstOrDefault(car => car.Model == "VW");
}
}
public string Make { get; set; }
public int Year { get; set; }
public Car DefaultCar { get; set; }
}
class Car
{
public string Model { get; set; }
}
}

As you are going to implement MVVM it will be a lot better if you start to think in objects to represent Cars in your application:
public class ViewModel
{
public Car SelectedCar{ get; set; }
public ObservableCollection<Car> Cars{
get {
var cars = new ObservableCollection(YOUR_DATA_STORE.Cars.ToList());
SelectedCar = cars.FirstOrDefault(car=>car.Model == "VW");
return cars;
}
}
}
public class Car
{
public string Model {get;set;}
public string Make { get; set; }
public int Year { get; set; }
}
Your Xaml:
<ComboBox SelectedItem="{Binding SelectedCar}", ItemsSource="{Binding Cars}"
UpdateSourceTrigger=PropertyChanged}"/>

Default Value:
If you set viewModel.Car = "VW", then it should auto-select that item in the combo box.
For this to work you will need to either implement INotifyPropertyChanged or set Car before you set DataContext.
INotifyPropertyChanged implementation might look like:
class ViewModel : INotifyPropertyChanged
{
private string car;
public ViewModel()
{
this.Car = "VW";
this.Cars = new ObservableCollection<string>() { "Mazda", "VW", "Audi" };
}
public string Car
{
get
{
return this.car;
}
set
{
if (this.car != value)
{
this.car = value;
OnPropertyChanged();
}
}
}
public ObservableCollection<string> Cars { get; }
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
2.
Bind ItemsSource and SelectedItem.
<ComboBox ItemsSource="{Binding Cars}"
SelectedItem="{Binding Car, Mode=TwoWay}">
</ComboBox>
You can also set ComboBox.ItemTemplate if your source or view is more complex than just displaying a string:
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" />
</DataTemplate>
</ComboBox.ItemTemplate>
In the view model just add a list property:
public ObservableCollection<string> Cars { get; set; }
It doesn't have to be ObservableCollection but that type will auto-update the UI whenever you change the collection.

Binding ComboBox SelectedItem using MVVM

I have a problem with the SelectedItem in my ComboBox.
<ComboBox Name="cbxSalesPeriods"
ItemsSource="{Binding SalesPeriods}"
DisplayMemberPath="displayPeriod"
SelectedItem="{Binding SelectedSalesPeriod}"
SelectedValuePath="displayPeriod"
IsSynchronizedWithCurrentItem="True"/>
If I open the ComboBox, I see the values.
If I select an item, the selected Item won't be shown.
Has anybody an idea?
In my ViewModel I have these two properties:
public ObservableCollection<SalesPeriodVM> SalesPeriods { get; private set; }
private SalesPeriodVM selectedSalesPeriod;
public SalesPeriodVM SelectedSalesPeriod
{
get { return selectedSalesPeriod; }
set
{
if (selectedSalesPeriod != value)
{
selectedSalesPeriod = value;
RaisePropertyChanged("SelectedSalesPeriod");
}
}
}
These are a few properties from the class :
public SalesPeriodVO Vo
{
get { return period; }
}
public int Year
{
get { return period.Year; }
set
{
if (period.Year != value)
{
period.Year = value;
RaisePropertyChanged("Year");
}
}
}
public int Month
{
get { return period.Month; }
set
{
if (period.Month != value)
{
period.Month = value;
RaisePropertyChanged("Month");
}
}
}
public string displayPeriod {
get
{
return this.ToString();
}
}
public override string ToString()
{
return String.Format("{0:D2}.{1}", Month, Year);
}
EDIT:
The Following happens If I remove the Property DisplayMemberPath:

You seem to be unnecessarily setting properties on your ComboBox. You can remove the DisplayMemberPath and SelectedValuePath properties which have different uses. It might be an idea for you to take a look at the Difference between SelectedItem, SelectedValue and SelectedValuePath post here for an explanation of these properties. Try this:
<ComboBox Name="cbxSalesPeriods"
ItemsSource="{Binding SalesPeriods}"
SelectedItem="{Binding SelectedSalesPeriod}"
IsSynchronizedWithCurrentItem="True"/>
Furthermore, it is pointless using your displayPeriod property, as the WPF Framework would call the ToString method automatically for objects that it needs to display that don't have a DataTemplate set up for them explicitly.
UPDATE >>>
As I can't see all of your code, I cannot tell you what you are doing wrong. Instead, all I can do is to provide you with a complete working example of how to achieve what you want. I've removed the pointless displayPeriod property and also your SalesPeriodVO property from your class as I know nothing about it... maybe that is the cause of your problem??. Try this:
public class SalesPeriodV
{
private int month, year;
public int Year
{
get { return year; }
set
{
if (year != value)
{
year = value;
NotifyPropertyChanged("Year");
}
}
}
public int Month
{
get { return month; }
set
{
if (month != value)
{
month = value;
NotifyPropertyChanged("Month");
}
}
}
public override string ToString()
{
return String.Format("{0:D2}.{1}", Month, Year);
}
public virtual event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged(params string[] propertyNames)
{
if (PropertyChanged != null)
{
foreach (string propertyName in propertyNames) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
PropertyChanged(this, new PropertyChangedEventArgs("HasError"));
}
}
}
Then I added two properties into the view model:
private ObservableCollection<SalesPeriodV> salesPeriods = new ObservableCollection<SalesPeriodV>();
public ObservableCollection<SalesPeriodV> SalesPeriods
{
get { return salesPeriods; }
set { salesPeriods = value; NotifyPropertyChanged("SalesPeriods"); }
}
private SalesPeriodV selectedItem = new SalesPeriodV();
public SalesPeriodV SelectedItem
{
get { return selectedItem; }
set { selectedItem = value; NotifyPropertyChanged("SelectedItem"); }
}
Then initialised the collection with your values:
SalesPeriods.Add(new SalesPeriodV() { Month = 3, Year = 2013 } );
SalesPeriods.Add(new SalesPeriodV() { Month = 4, Year = 2013 } );
And then data bound only these two properties to a ComboBox:
<ComboBox ItemsSource="{Binding SalesPeriods}" SelectedItem="{Binding SelectedItem}" />
That's it... that's all you need for a perfectly working example. You should see that the display of the items comes from the ToString method without your displayPeriod property. Hopefully, you can work out your mistakes from this code example.

I had a similar problem where the SelectedItem-binding did not update when I selected something in the combobox. My problem was that I had to set UpdateSourceTrigger=PropertyChanged for the binding.
<ComboBox ItemsSource="{Binding SalesPeriods}"
SelectedItem="{Binding SelectedItem, UpdateSourceTrigger=PropertyChanged}" />

<!-- xaml code-->
<Grid>
<ComboBox Name="cmbData" SelectedItem="{Binding SelectedstudentInfo, Mode=OneWayToSource}" HorizontalAlignment="Left" Margin="225,150,0,0" VerticalAlignment="Top" Width="120" DisplayMemberPath="name" SelectedValuePath="id" SelectedIndex="0" />
<Button VerticalAlignment="Center" Margin="0,0,150,0" Height="40" Width="70" Click="Button_Click">OK</Button>
</Grid>
//student Class
public class Student
{
public int Id { set; get; }
public string name { set; get; }
}
//set 2 properties in MainWindow.xaml.cs Class
public ObservableCollection<Student> studentInfo { set; get; }
public Student SelectedstudentInfo { set; get; }
//MainWindow.xaml.cs Constructor
public MainWindow()
{
InitializeComponent();
bindCombo();
this.DataContext = this;
cmbData.ItemsSource = studentInfo;
}
//method to bind cobobox or you can fetch data from database in MainWindow.xaml.cs
public void bindCombo()
{
ObservableCollection<Student> studentList = new ObservableCollection<Student>();
studentList.Add(new Student { Id=0 ,name="==Select=="});
studentList.Add(new Student { Id = 1, name = "zoyeb" });
studentList.Add(new Student { Id = 2, name = "siddiq" });
studentList.Add(new Student { Id = 3, name = "James" });
studentInfo=studentList;
}
//button click to get selected student MainWindow.xaml.cs
private void Button_Click(object sender, RoutedEventArgs e)
{
Student student = SelectedstudentInfo;
if(student.Id ==0)
{
MessageBox.Show("select name from dropdown");
}
else
{
MessageBox.Show("Name :"+student.name + "Id :"+student.Id);
}
}

Binding to a property within a static class instance

What I am trying to achieve
I have a WPF application (it's just for testing) and I want to bind the text (Content) of a label to a property somewhere. The idea is that this property value will be changed when the user chooses a different language. When the property changes, I want the label text to update with the new value.
What I have tried
I tried to create a static class with a static property for the label value. For example:
public static class Language
{
public static string Name = "Name";
}
I then was able to bind this value to my label using XAML like so:
Content="{Binding Source={x:Static lang:Language.Name}}"
And this worked fine for showing the initial value of "Name". The problem is, when the Name property changes the label value doesn't change.
So, back to the drawing board (Google). Then I found this answer which sounded exactly like what I needed. So here was my new attempt at this:
public class Language
{
public static Language Instance { get; private set; }
static Language() { Instance = new Language(); }
private Language() { }
private string name = "Name";
public string Name { get { return name; } set { name = value; } }
}
With my binding changed it this:
Content="{Binding Source={x:Static lang:Language.Instance}, Path=Name}"
This still results in the same problem.
Questions
What am I missing here? How can I get the label to update when the value is changed?

That simply isn't a property. Try:
public class Language
{
public static Language Instance { get; private set; }
static Language() { Instance = new Language(); }
private Language() { Name = "Name"; }
public string Name {get;private set;}
}
or with change notification:
public class Language : INotifyPropertyChanged
{
public static Language Instance { get; private set; }
static Language() { Instance = new Language(); }
private Language() { }
private string name = "Name";
public string Name
{
get { return name; }
set { SetValue(ref name, value);}
}
protected void SetValue<T>(ref T field, T value,
[CallerMemberName]string propertyName=null)
{
if (!EqualityComparer<T>.Default.Equals(field, value))
{
field = value;
OnPropertyChanged(propertyName);
}
}
protected virtual void OnPropertyChanged(
[CallerMemberName]string propertyName=null)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}