How to implement INotifyPropertyChanged in Xamarin.Forms
As a design methodology, its better to implement MVVM as a subclass and implement it to your ViewModel.
Sample Implementation:
public class ObservableProperty : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
I also strongly suggest implementing ICommand as a Dictionary structure like:
public abstract class ViewModelBase : ObservableProperty
{
public Dictionary<string,ICommand> Commands { get; protected set; }
public ViewModelBase()
{
Commands = new Dictionary<string,ICommand>();
}
}
So all todo in your ViewModel is just inherit the ViewModelBase class and use it
class LoginViewModel : ViewModelBase
{
#region fields
string userName;
string password;
#endregion
#region properties
public string UserName
{
get {return userName;}
set
{
userName = value;
OnPropertyChanged("UserName");
}
}
public string Password
{
get{return password;}
set
{
password = value;
OnPropertyChanged("Password");
}
}
#endregion
#region ctor
public LoginViewModel()
{
//Add Commands
Commands.Add("Login", new Command(CmdLogin));
}
#endregion
#region UI methods
private void CmdLogin()
{
// do your login jobs here
}
#endregion
}
Finally: Xaml Usage:
<Entry Placeholder="Username" Text="{Binding UserName}"/>
<Entry Placeholder="Password" Text="{Binding Password}" IsPassword="True"/>
<Button Text="Login" Command="{Binding Commands[Login]}"/>
Implementing INotifyPropertyChanged in my project Xamarin
Here is running screenshot.
You can achieve it like following format in your model.
public class MyObjets : INotifyPropertyChanged
{
// public string Designation { get; set; }
// public string Description { get; set; }
// public float Prix { get; set; }
// public int nbr_objet { get; set; }
int _nbr_objet;
public int Nbr_objet
{
get
{
return _nbr_objet;
}
set
{
if (_nbr_objet != value)
{
_nbr_objet = value;
OnPropertyChanged("Nbr_objet");
}
}
}
float _prix;
public float Prix
{
get
{
return _prix;
}
set
{
if (_prix != value)
{
_prix = value;
OnPropertyChanged("Prix");
}
}
}
string _designation;
public string Designation
{
get
{
return _designation;
}
set
{
if (_designation != value)
{
_designation = value;
OnPropertyChanged("Designation");
}
}
}
string _description;
public string Description
{
get
{
return _description;
}
set
{
if (_description != value)
{
_description = value;
OnPropertyChanged("Description");
}
}
}
public MyObjets(string Designation, string Description, float Prix, int nbr_objet)
{
this._designation = Designation;
this._description = Description;
this._prix = Prix;
this._nbr_objet = nbr_objet;
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Then Here is Layout.
<StackLayout>
<!-- Place new controls here -->
<Label Text="{Binding Designation}"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<Label Text="{Binding Description}"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<Label Text="{Binding Prix}"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<Label Text="{Binding Nbr_objet}"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
</StackLayout>
Here is layout backend code.
public MainPage()
{
InitializeComponent();
BindingContext = new MyObjets("xxxx","cccc",1.22f,11);
}
Here is my demo about MVVM with Listview, you can refer to it as well.
https://github.com/851265601/MVVMListview
If the reply is helpful, please do not forget to mark it as answer.
======================Update========================
You want to achieve the result like following GIF?
Here is your model
public class MyObjets
{
public string Designation { get; set; }
public string Description { get; set; }
public float Prix { get; set; }
public int nbr_objet { get; set; }
public MyObjets(string Designation, string Description, float Prix, int nbr_objet)
{
this.Designation = Designation;
this.Description = Description;
this.Prix = Prix;
this.nbr_objet = nbr_objet;
}
}
Here is ViewModelBase
public class ViewModelBase: INotifyPropertyChanged
{
public ViewModelBase()
{
ObjetVM = new MyObjets("ccc","xxx",1.2f,123);
}
public MyObjets ObjetVM { get; set; }
public int nbr_objet
{
get { return ObjetVM.nbr_objet; }
set
{
ObjetVM.nbr_objet = value;
OnPropertyChanged(nameof(ObjetVM.nbr_objet));
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyname)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}
}
Here layout forground code.
<StackLayout>
<Label Text="{Binding nbr_objet}"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand" />
<Button Text="change the value" Clicked="Button_Clicked"></Button>
</StackLayout>
here is layout background code.
public partial class MainPage : ContentPage
{
ViewModelBase viewModelBase;
public MainPage()
{
InitializeComponent();
viewModelBase = new ViewModelBase();
BindingContext = viewModelBase;
}
private void Button_Clicked(object sender, EventArgs e)
{
viewModelBase.nbr_objet = 111;
}
}
How can I implement INotifyPropertyChanged to make Xamarin binding update?I
this is how I implemented INotifyPropertyChanged.
public class Bindable : INotifyPropertyChanged
{
private Dictionary<string, object> _properties = new Dictionary<string, object>();
/// <summary>
/// Gets the value of a property
/// <typeparam name="T"></typeparam>
/// <param name="name"></param>
/// <returns></returns>
protected T Get<T>([CallerMemberName] string name = null)
{
object value = null;
if (_properties.TryGetValue(name, out value))
return value == null ? default(T) : (T)value;
return default(T);
}
/// <summary>
/// Sets the value of a property
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="value"></param>
/// <param name="name"></param>
protected void Set<T>(T value, [CallerMemberName] string name = null)
{
if (Equals(value, Get<T>(name)))
return;
_properties[name] = value;
OnPropertyChanged(name);
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Here is a sample class describing how to use
public class Transaction : Bindable
{
public Transaction()
{
this.TransactionDate = DateTimeOffset.Now;
this.TransactionType = TransactionType.Add; //enum
this.Quantity = 0;
this.IsDeleted = false;
this.Item = null; //object defined elsewhere
}
public Guid Id { get { return Get<Guid>(); } private set { Set<Guid>(value); } }
public DateTimeOffset? TransactionDate { get { return Get<DateTimeOffset?>(); } set { Set<DateTimeOffset?>(value); } }
public TransactionType TransactionType { get { return Get<TransactionType>(); } set { Set<TransactionType>(value); } }
public double? Quantity { get { return Get<double?>(); } set { Set<double?>(value); } }
public bool? IsDeleted { get { return Get<bool?>(); } set { Set<bool?>(value); } }
public byte[] RowVersion { get { return Get<byte[]>(); } private set { Set<byte[]>(value); } }
public virtual Guid? ItemId { get { return Get<Guid?>(); } set { Set<Guid?>(value); } }
public virtual Item Item { get { return Get<Item>(); } set { Set<Item>(value); } }
}
Xamarin using INotifyPropertyChanged binding with Entry and Label and MVVM
The model you changing in the Android project is not the same one as your bindingContext, so it doesn't work.
Solution:
Use messagingCenter to send the model from your Android project to your shared project and update the model there:
In the Android project, send the message everytime you scanned a barode:
public void DisplayResult(Intent intent)
{
// Output the scanned barcode to ViewModel
barcodeModel.decodedData = intent.GetStringExtra(Resources.GetString(Resource.String.datawedge_intent_key_data));
barcodeModel.decodedData = "test";
MessagingCenter.Send<object, BarcodeModel>(new object(), "barCodeScanned", barcodeModel);
}
In the shared project, subscribe to that message and update the model:
public partial class MainPage : ContentPage
{
BarcodeModel barCodeModel;
public MainPage()
{
InitializeComponent();
barCodeModel = new BarcodeModel();
barCodeModel.decodedData = "defaultValue";
this.BindingContext = barCodeModel;
MessagingCenter.Subscribe<object, BarcodeModel>(new object(), "barCodeScanned", (sender, arg) =>
{
BarcodeModel tempbarCodeModel = arg as BarcodeModel;
barCodeModel.decodedData = tempbarCodeModel.decodedData;
});
}
}
I uploaded my test project here and feel free to ask me any question.
after implementing iNotifypropertychanged in ViewModel SelectedItem is not working on listview
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();
}
}
}
INotifyPropertyChanged vs BindableObject vs ObservableObject in Xamarin.Forms/MAUI
I think your confusion is stemming from the difference between Bindable and Observable.
You're mostly correct about INotifyPropertyChanged. It's the abstract concept of a value changing, not the concrete implementation of that change. It's not just used for XAML though, it can be used for anything. But what do I mean by that?
Different parts of a system will care about why a value is changed for different reasons. A class that sits and silently logs data to a text file based on the value of something changing, is very different to a class that updates an application's user interface when something changes.
INotifyPropertyChanged is merely a mechanism to facilitate that change notification, it's nothing more.
Circling back to the difference between ObservableObject and BindableObject, they're simply for different use cases.
Take a look at the documentation I linked to above. See how many methods exist on the BindableObject class? Notice how OnPropertyChanged is just one of many methods on the BindableObject, but on ObservableObject it's one of only two?
BindableObject is used as a base class for elements. Changing the state of a button to disable it when it's clicked, for example. Or updating the text value of a Label in response to something changing.
ObservableObject can be used as a base class for anything that needs to notify some other class about a value change. As you correctly pointed out, it's to stop you needing to write that boilerplate INotifyPropertyChanged implementation all the time.
There's much more to this subject, but I don't want to bombard you with a huge amount of information.
If you're looking for some real world examples, study how the MVVM design pattern leverages the concept of classes communicating changes to one another.
Xamarin forms, working with a OnPropertyChanged with a INT value
You can proceed with something like that:
Make following changes to your App class and value1 property inside that class:
public static event PropertyChangedEventHandler PropertyChanged;
private static void OnPropertyChanged (string propertyName)
{
var changed = PropertyChanged;
if (changed != null)
{
PropertyChanged (null, new PropertyChangedEventArgs (propertyName));
}
}
private static int _value1;
public static int value1
{
get { return _value1; }
set
{
_value1 = value;
OnPropertyChanged("value1");
}
}
Then add this line to your StartPageViewModel constructor:
App.PropertyChanged += (sender, args) => OnPropertyChanged("currentValue");
In that code you are just leveraging PropertyChanged for your own purposes (you can even create your own event for that).
I mean StartPageViewModel subscribes to PropertyChanged event in Appclass, so it will be notified when value1 change. And when it actually occurs, then it is invoking his own PropertyChanged to notify View about currentValue change.
However, I would say better solution is to share View Model between MasterDetailPage and StartPage, because using global state makes your solution hard to understand :
public class SharedViewModel : INotifyPropertyChanged
{
private ICommand clickCommand;
private int currentValue;
/* INotifyPropertyChanged implementation */
public SharedViewModel()
{
ClickCommand = new Command(() => CurrentValue = CurrentValue + 1);
}
public ICommand ClickCommand
{
get { return clickCommand; }
set
{
clickCommand = value;
OnPropertyChanged("ClickCommand");
}
}
public int CurrentValue
{
get { return currentValue; }
set
{
currentValue = value;
OnPropertyChanged("CurrentValue");
}
}
}
And you need to use the same instance of SharedViewModel in MasterDetailPage as well as StartPage
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