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after implementing iNotifypropertychanged in ViewModel SelectedItem is not working on listview

Hello I am using MVVM in Xamarin Forms. I am trying to Bind my Listview's SeletedItem to my ViewModel. I binded it and worked fine. but when i have implemented INotifyPropertyChanged to update the view for some other component it stopped working.
I want it to work even INotifyPropertyChanged is implemented in my ViewModel. I am figuring out the problem why its happened. I searched on internet and Xamarin's documentation and could not find the reason.
My View
<ListView ItemsSource="{Binding PersonsList}"
CachingStrategy="RecycleElement"
HasUnevenRows="True"
SelectionMode="None"
SelectedItem="{Binding SelectedPerson}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="5">
<Label Text="{Binding FullName}"
FontSize="Medium"
TextColor="Orange"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
ViewModel
public class PersonViewModel : INotifyPropertyChanged
{
public PersonViewModel()
{
PersonsList = new ObservableCollection<User>
{
new User(){ UserId = 1, FullName = "John" },
new User(){ UserId = 2, FullName = "Alex" },
new User(){ UserId = 3, FullName = "Ellen" },
new User(){ UserId = 4, FullName = "Grace" }
};
}
public ObservableCollection<User> PersonsList { get; set; }
private User _selectedPerson { get; set; }
public User SelectedPerson
{
get { return _selectedPerson; }
set
{
if (_selectedPerson != value)
{
_selectedPerson = value;
OnPropertyChanged();
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Model
public class User
{
public int UserId { get; set; }
public string FullName { get; set; }
}
Hope to get some useful advice.

Change your SelectedPerson property to call OnPropertyChanged().
private User _selectedPerson { get; set; }
public User SelectedPerson
{
get { return _selectedPerson; }
set
{
if (_selectedPerson != value)
{
_selectedPerson = value;
OnPropertyChanged();
}
}
}

Wpf two way binding in listbox

trying to do two way binding in the listbox unfortunately does not work.
Here's the xaml code:
<ListBox Margin="19,0,21,149" ItemsSource="{Binding Items}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBox Text="{Binding Path=Name, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
<TextBlock Text="{Binding Path=Age}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
here's the viewmodel and person code:
public class ViewModel
{
public ObservableCollection<Person> Items
{
get
{
return new ObservableCollection<Person>
{
new Person { Name = "P1", Age = 1 },
new Person { Name = "P2", Age = 2 }
};
}
}
}
public class Person : INotifyPropertyChanged
{
public string _name;
public int Age { get; set; }
public string Name
{
get
{
return _name;
}
set
{
if (value != _name)
{
_name = value;
OnPropertyChanged("Name");
}
}
}
private void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
and MainWindow:
public MainWindow()
{
InitializeComponent();
model = new ViewModel();
this.DataContext = model;
}
I do not know what is wrong, trying to bind the property "Name", but it does not work. Please, let me know what may be wrong.

It was enough to change:
public class ViewModel
{
ObservableCollection<Person> _items = new ObservableCollection<Person>
{
new Person { Name = "P1", Age = 1 },
new Person { Name = "P2", Age = 2 }
};
public ObservableCollection<Person> Items
{
get
{
return _items;
}
}
}

Xamarin Forms Binding not showing on ListView

I'm new to Xamarin and I'm trying to bind my ViewModel to the View but I couldn't do it yet.
Here's the code.
(Model)
namespace CadastroProdutos
{
public class Produto
{
public string Codigo { get; set; }
public string Identificacao { get; set; }
public string Tipo { get; set; }
}
}
(Observable Model)
namespace CadastroProdutos
{
public class ObservableProduto : INotifyPropertyChanged
{
Produto produto;
public ObservableProduto()
{
produto = new Produto()
{
Identificacao = "Primeiro",
Codigo = "123456"
};
produto = new Produto()
{
Identificacao = "Segundo",
Codigo = "123456"
};
produto = new Produto()
{
Identificacao = "Terceiro",
Codigo = "123456"
};
}
public event PropertyChangedEventHandler PropertyChanged;
public string Codigo
{
set
{
if (!value.Equals(produto.Codigo, StringComparison.Ordinal))
{
produto.Codigo = value;
OnPropertyChanged("Codigo");
}
}
get
{
return produto.Codigo;
}
}
public string Identificacao
{
set
{
if (!value.Equals(produto.Identificacao, StringComparison.Ordinal))
{
produto.Identificacao = value;
OnPropertyChanged("Identificacao");
}
}
get
{
return produto.Identificacao;
}
}
public string Tipo
{
set
{
if (!value.Equals(produto.Tipo, StringComparison.Ordinal))
{
produto.Tipo = value;
OnPropertyChanged("Tipo");
}
}
get
{
return produto.Tipo;
}
}
void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler == null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
(ViewModel)
namespace CadastroProdutos
{
public class ListProdutoViewModel
{
ObservableCollection<ObservableProduto> produtos;
public ListProdutoViewModel()
{
produtos = new ObservableCollection<ObservableProduto>();
}
public ObservableCollection<ObservableProduto> Produtos
{
set
{
if (value != produtos)
{
produtos = value;
}
}
get
{
return produtos;
}
}
}
}
(View)
<?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:CadastroProdutos;"
x:Class="CadastroProdutos.ListProduto"
Title="Listagem de Produtos">
<ContentPage.Content>
<ListView x:Name="listView" Margin="20,40,20,20" ItemsSource="{Binding Produtos}">
<ListView.BindingContext>
<local:ListProdutoViewModel />
</ListView.BindingContext>
<ListView.Header>
<StackLayout Orientation="Vertical" >
<Label Text="Produtos" HorizontalOptions="Center"/>
</StackLayout>
</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<StackLayout Orientation="Horizontal" >
<TextCell Text="{Binding Identificacao}"/>
</StackLayout>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</ContentPage.Content>
</ContentPage>
It not worked, It didn't show those elements on the list. Can someone help me?
Thanks in advance.

You're not quite understanding the MVVM approach, but you're almost there. You don't need to have the ObservableProduto class. You can make your Produto class your model.
This is your Produto model. I went ahead and changed it up for you.
namespace CadastroProdutos
{
public class Produto : INotifyPropertyChanged
{
private string codigo;
public string Codigo
{
get {return codigo;}
set {codigo=value; OnPropertyChanged(); }
}
private string identificacao;
public string Identificacao
{
get {return identificacao;}
set {identificacao=value; OnPropertyChanged(); }
}
private string tipo ;
public string Tipo
{
get {return tipo;}
set {tipo=value; OnPropertyChanged(); }
}
public event PropertyChangedEventHandler PropertyChanged;
void OnPropertyChanged([CallerMemberName]string propertyName = "") =>
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
You should contain an ObservableCollection of your Produtos in a viewmodel. I see you've done that. I've edited it a bit. You may need to be careful about totally resetting your ObservableCollection on a set.
namespace CadastroProdutos
{
public class ListProdutoViewModel
{
ObservableCollection<Produto> produtos;
public ListProdutoViewModel()
{
produtos = new ObservableCollection<Produto>();
}
public ObservableCollection<Produto> Produtos
{
set
{
if (value != produtos)
{
produtos = value;
}
}
get
{
return produtos;
}
}
}
}
Note: you will need to add items to your ObservableColleciton still.

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();
}
}

C# WPF MVVM ComboBox SelectedItem

I know that it's been here a million times but I don't know what's wrong in my code. I tried everything but the ComboBox is not binding SelectedItem correctly.
Here is my complete sandbox solution. You can also find it on GitHub (https://github.com/LukasNespor/ComboBoxBinding).
BindableBase.cs
public class BindableBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public virtual void RaisePropertyChanged(string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
ContactModel.cs
public class ContactModel : BindableBase
{
private int _Id;
public int Id
{
get { return _Id; }
set
{
_Id = value;
RaisePropertyChanged(nameof(Id));
}
}
private string _Name;
public string Name
{
get { return _Name; }
set
{
_Name = value;
RaisePropertyChanged(nameof(Name));
}
}
private string _Phone;
public string Phone
{
get { return _Phone; }
set
{
_Phone = value;
RaisePropertyChanged(nameof(Phone));
}
}
public override bool Equals(object obj)
{
if (obj != null || !(obj is ContactModel))
return false;
return ((ContactModel)obj).Id == this.Id;
}
public override string ToString()
{
return $"{Name} {Phone}";
}
}
MainWindow.xaml
<Window x:Class="WpfApplication1.MainWindow"
...>
<Grid>
<ComboBox Width="200" Height="23"
SelectedItem="{Binding ViewModel.SelectedContact}" ItemsSource="{Binding ViewModel.Contacts}" />
</Grid>
MainWindows.xaml.cs
public partial class MainWindow : Window
{
public MainViewModel ViewModel { get; set; }
public MainWindow()
{
InitializeComponent();
DataContext = this;
ViewModel = new MainViewModel();
ViewModel.SelectedContact = new ContactModel
{
Id = 2,
Name = "Some Guy",
Phone = "+123456789"
};
}
}
MainViewModel.cs
public class MainViewModel : BindableBase
{
public List<ContactModel> Contacts
{
get
{
return new List<ContactModel>
{
new ContactModel() {Id = 1, Name = "John Doe", Phone = "+166666333" },
new ContactModel() {Id = 2, Name = "Some Guy", Phone = "+123456789" }
};
}
}
private ContactModel _SelectedContact;
public ContactModel SelectedContact
{
get { return _SelectedContact; }
set
{
_SelectedContact = value;
RaisePropertyChanged(nameof(SelectedContact));
}
}
}

You need do Sync the list with the current selected item:
1.Xaml:
<ComboBox ItemsSource="{Binding Contacts}" SelectedItem="{Binding SelectedContact}" IsSynchronizedWithCurrentItem="True" />
2.ViewModel:
public ObservableCollection<ContactModel> Contacts { get; set; }
public MainViewModel()
{
_model = new Model {Name = "Prop Name" };
Contacts = new ObservableCollection<ContactModel>
{
new ContactModel {Id = 1, Name = "John Doe", Phone = "+166666333"},
new ContactModel {Id = 2, Name = "Some Guy", Phone = "+123456789"}
};
SelectedContact = Contacts[0];
}
private ContactModel _SelectedContact;
public ContactModel SelectedContact
{
get { return _SelectedContact; }
set
{
_SelectedContact = value;
OnPropertyChanged(nameof(SelectedContact));
}
}