Develop Reference

How to create a program with one model and multiple viewmodel?

I have multiple views (usercontrols) and a model in my program. I've created viewmodel classes for each view. The problem is, I don't know what is the best structure for this purpose. I want to create one model instance and use it in multiple viewmodels. Could you please suggest me a structure or a way to do this?
Model.cs
public class Model
{
....
public string NameModel1 = "Mike";
public string NameModel2 = "George";
}
ViewModel1.cs
public class ViewModel1 : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
....
private string nameViewModel1;
public string NameViewModel1
{
get
{
return value;
}
set
{
if(nameViewModel1!=value)
{
nameViewModel1=value;
OnPropertyChanged();
}
}
}
}
ViewModel2.cs
public class ViewModel2 : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
....
private string nameViewModel2;
public string NameViewModel2
{
get
{
return value;
}
set
{
if(nameViewModel2!=value)
{
nameViewModel2=value;
OnPropertyChanged();
}
}
}
}
How can I equalize NameModel1 value to NameViewModel1 value and NameModel2 value to NameViewModel2 value by creating the model instance once?

Model and ViewModel Consept MVVM WPF

I want to read some data from database and do some process on them and then view them in the view.
I read a lot about MVVM and now I am confused.
Imaging I read a person entity from database with Name attribute.
please make a small code and show me how should I make my model and ViewModel.
I guess it we will be something like this :
public class PersonModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string Name;
public string name
{
get
{
return Name;
}
set
{
Name = value;
onpropertychanged("name");
}
}
public PersonModel( string s)
{
name = s;
}
public void onpropertychanged(string PName)
{
if (PropertyChanged !=null)
{
PropertyChanged(this, new PropertyChangedEventArgs(PName));
}
}
}
public class PersonViewModel
{
public ObservableCollection <PersonModel> list { get; set; }
public PersonViewModel()
{
list = new ObservableCollection<model>();
list.Add(new model("abc"));
list.Add(new model("def"));
}
public void change()
{
list[1].name = "changed";
}
}
public class ViewModelBase
{
public PersonViewModel vperson { get; set; }
public ViewModelBase()
{
vperson = new PersonViewModel();
vperson.change();
}
}
Edite : Where should database connections be?
Edite :
<Grid>
<TextBox Text="{Binding vperson.list[1].name}" />
</Grid>
</Window>

I edited your classes and is working
public class PersonModel : INotifyPropertyChanged
{
private string _name;
public string Name
{
get => _name;
set
{
if (_name == value) return;
_name = value;
OnPropertyChanged();
}
}
public PersonModel(string name)
{
_name = name;
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public class PersonViewModel
{
public ObservableCollection<PersonModel> Items { get; set; }
public PersonViewModel()
{
Items = new ObservableCollection<PersonModel> { new PersonModel("abc"), new PersonModel("def") };
}
public void Change()
{
Items[1].Name = "changed";
}
}
public class ViewModelBase
{
public PersonViewModel PersonViewModel { get; set; }
public ViewModelBase()
{
PersonViewModel = new PersonViewModel();
PersonViewModel.Change();
}
}
//Use the dataContext in this way, will help you with the strong type
xmlns:viewModels="clr-namespace:WpfApp1.ViewModels"
<Window.DataContext>
<viewModels:ViewModelBase />
</Window.DataContext>
<Grid>
<TextBox Text="{Binding PersonViewModel.Items[1].Name}" />
</Grid>

observable collection not changing combobox

I have an observable collection which is the item source to a combo box. When I add a new item to the observable collection, it appears in the combobox. However, when I update an existing item, it does not update the combo box. What am I doing wrong?
xaml:
<ComboBox ItemsSource="{Binding ChildGroupOC}" DisplayMemberPath="childGroupName" />
observable collection property:
public ObservableCollection<ChildGroupBO> ChildGroupOC
{
get
{ return childGroupOC;}
set
{
childGroupOC = value;
}
}
public class ChildGroupBO: INotifyPropertyChanged
{
public int parentGroupId { get; set; }
public int childGroupId { get; set; }
public string childGroupName { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
}

Your implementation of ChildGroupComboBoxBO not only has to implement INotifyPropertyChanged but also call the event on changes:
OnPropertyChanged("parentGroupId");
Example from MSDN:
public class Person : INotifyPropertyChanged
{
private string name;
// Declare the event
public event PropertyChangedEventHandler PropertyChanged;
public Person()
{
}
public Person(string value)
{
this.name = value;
}
public string PersonName
{
get { return name; }
set
{
name = value;
// Call OnPropertyChanged whenever the property is updated
OnPropertyChanged("PersonName");
}
}
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}

Where i need to define INotifyPropertyChanged in case of Base and sub classes

i have this Base class:
public abstract class WiresharkFile
{
protected string _fileName;
protected int _packets;
protected int _packetsSent;
protected string _duration;
public int Packets
{
get { return _packets; }
set { _packets = value; }
}
public int PacketsSent
{
get { return _packetsSent; }
set { _packetsSent = value; }
}
}
And this sub class:
public class Libpcap : WiresharkFile, IDisposable, IEnumerable<WiresharkFilePacket>
{
....
}
Create my object:
WiresharkFile wiresahrkFile = new Libpcap(file);
My collection:
public ObservableCollection<WiresharkFile> wiresharkFiles { get; set; }
Send packets:
wiresahrkFile.Sendpackets();
At this point all my wiresahrkFile (Libpcap type) properties is changing so i wonder where i need to define this INotifyPropertyChanged.

If your xaml is binded to properties of WiresharkFile then a WiresharkFile have to implement the INotifyPropertyChanged, if not it will lead to the memory leaks (Top 3 Memory Leak Inducing Pitfalls of WPF Programming). If your binding is defined only on a Libpcap class then the Libpcap have to implement the INotifyPropertyChanged interface. In my projects I create a base implementation of the INotifyPropertyChanged interface ,and then each base models and base view models just inherits from that implementation. Here some base code:
1. Base implementation:
public class BaseObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged<T>(Expression<Func<T>> raiser)
{
var propName = ((MemberExpression)raiser.Body).Member.Name;
OnPropertyChanged(propName);
}
protected bool Set<T>(ref T field, T value, [CallerMemberName] string name = null)
{
if (!EqualityComparer<T>.Default.Equals(field, value))
{
field = value;
OnPropertyChanged(name);
return true;
}
return false;
}
}
2. Your model (in my opinion):
public abstract class WiresharkFile:BaseObservableObject
{
private string _fileName;
private int _packets;
private int _packetsSent;
private string _duration;
public int Packets
{
get { return _packets; }
set
{
_packets = value;
OnPropertyChanged();
}
}
public int PacketsSent
{
get { return _packetsSent; }
set
{
_packetsSent = value;
OnPropertyChanged();
}
}
}
regards,

Same answer with IIan but for C# 8 and .Net Framework 4.8.
1. Base Model
public class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged<T>(Expression<Func<T>> raiser)
{
string propName = ((MemberExpression)raiser?.Body).Member.Name;
OnPropertyChanged(propName);
}
protected bool Set<T>(ref T field, T value, [CallerMemberName] string name = null)
{
if (!EqualityComparer<T>.Default.Equals(field, value))
{
field = value;
OnPropertyChanged(name);
return true;
}
return false;
}
}
2. Your Model
public class Current : ObservableObject
{
private string _status;
public Current()
{
Status = "Not Connected";
}
public string Status
{
get { return _status; }
set
{
_status = value;
OnPropertyChanged(); // call this to update
}
}
}
3. How to use?
<Label Content="{Binding Status}"/>

Binding a nested object to a DataGrid in c# WPF

I am trying to bind the data displayed in a DataGrid to a dynamic list of object (WhisperModel) which is inside another object(WhisperReader). The DataGrid only displays the headers, but no values. How can I make the DataGrid dynamically update itself when the list "whispers" is changed?
Main Window XAML:
<DataGrid x:Name="whisperDataGrid" Margin="10,69,10,10" IsReadOnly="True" ItemsSource="{Binding}"/>
Main Window C#
public partial class MainWindow : Window
{
private WhisperReader wr;
public MainWindow()
{
InitializeComponent();
wr = new WhisperReader();
whisperDataGrid.DataContext = wr.whispers;
}
WhisperReader:
class WhisperReader
{
public ObservableCollection<WhisperModel> whispers { get; private set; }
public WhisperReader()
{
whispers = new ObservableCollection<WhisperModel>();
}
WhisperModel:
class WhisperModel
{
public DateTime sentTime { get; set; }
public string sender { get; set; }
public string message { get; set; }
}

I think your problem is that it doesn't know when to update itself because:
You have made the whispers list the data context.
The properties that you are binding to don't use INotifyPropertyChanged.
WhisperReader and WhisperModel are not public
All bindings must be public, must be properties, and must call the PropertyChanged method.
The PropertyChanged function triggers the binding updates.
Try this...
public partial class MainWindow : Window
{
private WhisperReader wr;
public MainWindow()
{
InitializeComponent();
wr = new WhisperReader();
whisperDataGrid.DataContext = wr;
}
public class WhisperReader : INotifyPropertyChanged
{
ObservableCollection<WhisperModel> _whispers;
public ObservableCollection<WhisperModel> whispers
{
get { return _whispers; }
private set
{
_whispers = value;
NotifyPropertyChanged();
}
}
public WhisperReader()
{
whispers = new ObservableCollection<WhisperModel>();
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public class WhisperModel : INotifyPropertyChanged
{
public DateTime sentTime { get; set; }
private string _sender;
public string sender
{
get { return _sender; }
set { _sender = value; NotifyPropertyChanged();
}
private string _message;
public string message
{
get { return _message; }
set { _message = value; NotifyPropertyChanged();
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
<DataGrid x:Name="whisperDataGrid" Margin="10,69,10,10" IsReadOnly="True" AutoGenerateColumns="True" ItemsSource="{Binding whispers}"/>