Hi we would to handler the event OnPropertyChanged and gets the value in all application forms of this variable.
using System;
using System.ComponentModel;
using System.Windows;
public partial class App : INotifyPropertyChanged
{
#region - Connected -
/// <summary>
/// Gets or sets Connected status
/// </summary>
private Boolean connected = false;
public Boolean Connected
{
get { return connected; }
set
{
if(connected != value)
{
connected = value;
OnPropertyChanged("Connected");
}
}
}
#endregion - Connected -
#region - INotifyPropertyChanged implementation -
// Basically, the UI thread subscribes to this event and update the binding if the received Property Name correspond to the Binding Path element
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
#endregion - INotifyPropertyChanged implementation -
}
how can fired this event "OnPropertyChanged" and get the value Connected On all App's windows.
On the surface, this looks as simple as each form calling
(Application.Current as App).PropertyChanged += ....
And in your handler, use
(sender as App).Connected
to get the value of that property.
Related
For building the WPF application I used VS2022 (V17.4.4) and NuGet Fody.PropertyChanged Package (V4.1.0).
If a property is set directly, the PropertyChanged event will be raised for the property itself and all the [DependsOn] properties as well.
But if only the underlying field of the property is set and the PropertyChanged event is raised later manually by call of RaisePropertyChanged(nameof(Property)) the [DependsOn] properties will not raise any PropertyChanged event.
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace FodyPropertyChanged
{
[PropertyChanged.AddINotifyPropertyChangedInterface]
public class MainWindowViewModel : INotifyPropertyChanged
{
private DeviceStates _DeviceState;
private event PropertyChangedEventHandler _propertyChanged;
public event PropertyChangedEventHandler PropertyChanged
{
add { _propertyChanged += value; }
remove
{
if (_propertyChanged != null)
_propertyChanged -= value;
}
}
public DeviceStates DeviceState
{
get { return _DeviceState; }
set { _DeviceState = value; }
}
[PropertyChanged.DependsOn(nameof(DeviceState))]
public bool IsBusy
{
get { return DeviceState == DeviceStates.Working; }
}
public void SetDeviceStateTo(DeviceStates deviceState)
{
DeviceState = deviceState;
}
public void SetDeviceStateToAndRaisePropertyChangedAfterwards(DeviceStates deviceState)
{
_DeviceState = deviceState;
RaisePropertyChanged(nameof(DeviceState));
}
private void RaisePropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChangedEventHandler handler = _propertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
If I call SetDeviceStateTo(...) the PropertyChanged event will be raised for DeviceState and IsBusy (GUI will be updated, correctly). But if I call SetDeviceStateToAndRaisePropertyChangedAfterwards(...) the PropertyChanged event will be raised for DeviceState, only (IsBusy bindings will not be updated).
Any idea?
Like canton7 and BionicCode said:
[DependsOn] is only working for the setter not for events. So it is a known limitation and not a bug.
I'm playing with databinding on c# compact framework. I develop a simple form with a Textbox and a Label. I want to change the data binded to Textbox (bindModelTextBox) and show these changes by the Label (bindModelLabel), which is binded to the same data. Here is the code:
public partial class CreateShipment : Form {
//simple bean. Just one property: id, a string
private BasicShipmentBean toBindBasicShipment = null;
public CreateShipment() {
InitializeComponent();
BindingSource bsProva = new BindingSource();
toBindBasicShipment = new BasicShipmentBean();
toBindBasicShipment.id = "boo";
bsProva.Add(toBindBasicShipment);
bindModelLabel.DataBindings.Add("Text", bsProva, "id", true, DataSourceUpdateMode.OnPropertyChanged);
bindModelTextBox.DataBindings.Add("Text", bsProva, "id", true, DataSourceUpdateMode.OnPropertyChanged);
bindModelTextBox.LostFocus += textLoseFocus;
}
...
private void textLoseFocus(object sender, System.EventArgs e)
{
System.Diagnostics.Debug.WriteLine("focus lost. "+toBindBasicShipment.id);
}
When textbox loose focus I can see the data is updated in the bean, but, the label still shows bean's original id value. What am I missing?
You need to implement INotifyPropertyChanged on your BasicShipmentBean class. I forgot where exactly I found this originally, but here is an ObservableObject base class that implements INotifyPropertyChanged, that I use for all of my data sources.
public abstract class ObservableObject : INotifyPropertyChanged
{
#region Debugging Aides
/// <summary>
/// Warns the developer if this object does not have
/// a public property with the specified name. This
/// method does not exist in a Release build.
/// </summary>
[Conditional("DEBUG")]
[DebuggerStepThrough]
public virtual void VerifyPropertyName(string propertyName)
{
// Verify that the property name matches a real,
// public, instance property on this object.
if (TypeDescriptor.GetProperties(this)[propertyName] == null)
{
string msg = "Invalid property name: " + propertyName;
if (this.ThrowOnInvalidPropertyName)
throw new Exception(msg);
else
Debug.Fail(msg);
}
}
/// <summary>
/// Returns whether an exception is thrown, or if a Debug.Fail() is used
/// when an invalid property name is passed to the VerifyPropertyName method.
/// The default value is false, but subclasses used by unit tests might
/// override this property's getter to return true.
/// </summary>
protected virtual bool ThrowOnInvalidPropertyName { get; private set; }
#endregion // Debugging Aides
#region INotifyPropertyChanged Members
/// <summary>
/// Raises the PropertyChange event for the property specified
/// </summary>
/// <param name="propertyName">Property name to update. Is case-sensitive.</param>
public virtual void RaisePropertyChanged(string propertyName)
{
this.VerifyPropertyName(propertyName);
OnPropertyChanged(propertyName);
}
/// <summary>
/// Raised when a property on this object has a new value.
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Raises this object's PropertyChanged event.
/// </summary>
/// <param name="propertyName">The property that has a new value.</param>
protected virtual void OnPropertyChanged(string propertyName)
{
this.VerifyPropertyName(propertyName);
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs(propertyName);
handler(this, e);
}
}
#endregion // INotifyPropertyChanged Members
}
Then, you need to raise the OnPropertyChanged event in your setter for the id in BasicShipmentBean, e.g.:
private string _id;
public string id
{
get { return _id; }
set
{
if (value != _id)
{
_id = value;
OnPropertyChanged("id");
}
}
}
Data binding in the Compact Framework is a bit more tedious than in WPF, but much of the implementation is pretty similar.
I have an MVVM app, where my ViewModel PingerViewModel processes incoming WCF Ping() messages. Processing such a message happens on a thread of Scheduler.Default's thread pool.
Semantically, incoming WCF messages change a bound property CanPing and raise the PropertyChanged event for said property.
But my UI is not updating until it receives some UI event, e.g. focusing/clicking the window, etc.
How do I make it update as soon as the event is fired?
I have tried raising the PropertyChanged event...
on the Application's Dispatcher,
using a SynchronizationContext
without any luck.
I also verified that the bound property is indeed set to the proper value, and that there is indeed a listener consuming my PropertyChanged event.
Here's some code (full code on github):
part of my view's MainWindow.xaml:
It might be worth noting that the bound Command does not actually play a role in producing the incoming WCF message.
<Button Content="Ping" Height="23" HorizontalAlignment="Left" Margin="10,10,0,0" Name="PingBtn" VerticalAlignment="Top" Width="75" AutomationProperties.AutomationId="Ping"
IsEnabled="{Binding CanPing}"
Command="{Binding PingCommand}" />
part of my views MainWindow.xaml.cs
public MainWindow()
{
DataContext = new PingerViewModel();
InitializeComponent();
}
part of my ViewModel
public class PingerViewModel : INotifyPropertyChanged
public PingerViewModel()
{
Pinger = new Pinger(true);
PingCommand = new PingerPingCommand(this);
//...
}
public bool CanPing
{
get
{
if (Pinger == null) return false;
return Pinger.CanPing;
}
}
public void Ping()
{
_pingClient.Channel.Ping();
Pinger.CanPing = false;
OnPropertyChanged("CanPing");
}
protected virtual void OnPong(PongEventArgs e)
{
Pinger.CanPing = true;
OnPropertyChanged("CanPing");
}
public Pinger Pinger { get; private set; }
public ICommand PingCommand { get; private set; }
//...
}
I think you need to remove IsEnabled="{Binding CanPing}" from your button.
Binding to the command is enough as the ICommand object contains CanExecute and the CanExecuteChanged event handler.
I would create a CanExecute boolean inside your Command class, and implement INotifyPropertyChanged also on this class. Something like this:
public class PingCommand : ICommand, INotifyPropertyChanged
{
private bool _canExecute;
public bool CanExecute1
{
get { return _canExecute; }
set
{
if (value.Equals(_canExecute)) return;
_canExecute = value;
CanExecuteChanged.Invoke(null, null);
OnPropertyChanged("CanExecute1");
}
}
public void Execute(object parameter)
{
//whatever
}
public bool CanExecute(object parameter)
{
return _canExecute;
}
public event EventHandler CanExecuteChanged;
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Then, on the Ping/Pong methods inside your ViewModel, update this property inside your Command:
public void Ping()
{
_pingClient.Channel.Ping();
Pinger.CanPing = false;
PingCommand.CanExecute1 = false;
OnPropertyChanged("CanPing");
}
protected virtual void OnPong(PongEventArgs e)
{
Pinger.CanPing = true;
PingCommand.CanExecute1 = true;
OnPropertyChanged("CanPing");
}
if your CanPing Property and the CanExecute methode for your PingCommand both return TRUE it should work.
sometimes the Delegate/RelayCommand implementation give the possibility to call RaiseCanExecuteChanged() - try this if the statement above is true for both and its not working
btw this is called within the RaiseCanExecuteChanged()
CommandManagerHelper.CallWeakReferenceHandlers(_canExecuteChangedHandlers);
You can use RaiseCanExecuteChanged() method of the said property to update.
Eg:
this.PingCommand.RaiseCanExecuteChanged();
Try this, I hope it will solve your problem.
I am just getting started with MVVM so apologies if I've done something really stupid. I tried writing a very simple test to see if I could remember everything, and for the life of me I can't see why its not working.
In my view I have a textBox where its text property is bound to a value in the ViewModel. Then when pressing a button the value should be altered and the textBox update.
I can see the value does alter (I have added a MessageBox.Show() line in the buttom press command) however the textBox does not update.
I assume that this means I have not properly implemented the INotifyPropertyChanged event properly but am unable to see my mistake.
Could anyone point me in the right direction?
Here is the code:
View
<Window x:Class="Mvvm.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<StackPanel Orientation="Horizontal" VerticalAlignment="Top">
<TextBox Height="40" Width="200" Text="{Binding helloWorld.Message, UpdateSourceTrigger=PropertyChanged}"/>
<Button Command="{Binding UpdateTimeCommand}">Update</Button>
</StackPanel>
</Window>
Behind View
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = new ViewModel.MainWindowViewModel();
}
}
ViewModel
namespace Mvvm.ViewModel
{
internal class MainWindowViewModel
{
private HelloWorld _helloWorld;
/// <summary>
/// Creates a new instance of the ViewModel Class
/// </summary>
public MainWindowViewModel()
{
_helloWorld = new HelloWorld("The time is " + DateTime.Now.ToString("HH:mm:ss"));
UpdateTimeCommand = new Commands.UpdateTimeCommand(this);
}
/// <summary>
/// Gets the HellowWorld instance
/// </summary>
public HelloWorld helloWorld
{
get
{
return _helloWorld;
}
set
{
_helloWorld = value;
}
}
/// <summary>
/// Updates the time shown in the helloWorld
/// </summary>
public void UpdateTime()
{
helloWorld = new HelloWorld("The time is " + DateTime.Now.ToString("HH:mm:ss"));
}
public ICommand UpdateTimeCommand
{
get;
private set;
}
}
Model
namespace Mvvm.Model
{
class HelloWorld : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public HelloWorld(string helloWorldMessage)
{
Message = "Hello World! " + helloWorldMessage;
}
private string _Message;
public string Message
{
get
{
return _Message;
}
set
{
_Message = value;
OnPropertyChanged("Message");
}
}
private void OnPropertyChanged(string p)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(p));
}
}
}
}
Commands
namespace Mvvm.Commands
{
internal class UpdateTimeCommand : ICommand
{
private ViewModel.MainWindowViewModel _viewModel;
public UpdateTimeCommand(ViewModel.MainWindowViewModel viewModel)
{
_viewModel = viewModel;
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
_viewModel.UpdateTime();
}
}
}
Sorry for such a long post and it being a spot my mistake post but I've looked at it for so long and I don't know what I'm doing wrong
Thanks!
The Problem that you have is that you are changing the wrong Property. Instead of changing the HelloWorld.Message Property, you are changing MainWindowViewModel.HelloWorld property. Your code will work OK if you change this line:
public void UpdateTime()
{
helloWorld = new HelloWorld("The time is " + DateTime.Now.ToString("HH:mm:ss"));
}
For this one
public void UpdateTime()
{
helloWorld.Message = "The time is " + DateTime.Now.ToString("HH:mm:ss");
}
If you want to keep your original code, then you need to implement INotifyPropertyChanged for your ViewModel, and rise the event when you change helloWorld object.
Hope this helps
I think you need to implement PropertyChanged notification on your ViewModel. You are creating a new HelloWorld in the UpdateTime method, but the UI doesn't know it.
Edit
I have a ViewModel base class which I derive all of my ViewModels from. It implements INotifyPropertyChanged, and has references to my relay command classes, and some other common stuff. I recommend always having INotifyPropertyChanged implemented on the ViewModel. The ViewModel is there to expose data to the UI, and it cant do that for data that changes without that interface.
i think your ViewModel needs to implement INotifyPropertyChanged too,
or you can set the DataContext before you call InitializeComponents(), if you do that you should change your code to NOT create a new instance every update like Agustin Meriles said.
i think you mistake Model and VM: Model is MainWindowViewModel and VM is HelloWorld
In your VM (class HelloWorld ) you need use your model
So, your classes will look like:
using System.ComponentModel;
namespace WpfApplication1
{
public sealed class TextVM : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private TextInfo _info;
public TextVM()
{
_info = new TextInfo();
}
public string MyText
{
get { return _info.MyText; }
set
{
_info.MyText = value;
OnPropertyChanged("MyText");
}
}
private void OnPropertyChanged(string p)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(p));
}
}
}
}
using System;
namespace WpfApplication1
{
public sealed class TextInfo
{
public TextInfo()
{
MyText = String.Empty;
}
public string MyText { get; set; }
}
}
inset inside your ICommands
I apologize for the newbie question, but I am struggling with this problem. I have the following TextBlock defined:
<TextBlock Text="{Binding Source={x:Static local:DeviceManager.Instance},
Path=Player.CurrentArtist}"></TextBlock>
The DeviceManager is a singleton that functions as a facade for other classes. For example, Player is a property of type IPlayer which represents an music-playing application. I would like the TextBlock to display the artist that is currently playing, which is periodically updated in the Player.CurrentArtist property.
Unfortunately, I cannot get the TextBlock to update when the CurrentArtist property updates. Both the DeviceManager and the IPlayer implement INotifyPropertyChanged, but when I step through the application, the DeviceManager does not have an event handler attached to it.
Does anyone have a suggestion for how to update the text block while preserving the singleton-facade?
Here is the code for the INotifyPropertyChanged members in both the DeviceManager and the IPlayer subclass:
public sealed class DeviceManager : INotifyPropertyChanged
{
// Singleton members omitted
public IPlayer Player
{
get { return player; }
set
{
this.player = value;
player.PropertyChanged += new PropertyChangedEventHandler(device_PropertyChanged);
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void device_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(sender, e);
}
}
#endregion
}
class MediaPlayer : IPlayer
{
private string artist;
private string title;
public event PropertyChangedEventHandler PropertyChanged;
public void Play(string artist, string title)
{
this.artist = artist;
this.title = title;
OnPropertyChanged("Player:Song");
}
private void OnPropertyChanged(string p)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(p));
}
}
public string CurrentTitle
{
get { return title; }
}
public string CurrentArtist
{
get { return artist; }
}
}
The problem is that WPF is never notified of the value of the CurrentArtist property changing. You can either implement a private setter for the CurrentArtist property, which will trigger the PropertyChanged event, or trigger a PropertyChanged event for the CurrentArtist property in MediaPlayer.Play().
WPF only responds to PropertyChanged if the name you pass in (i.e. right now "Player:Song") is the same as the property you're bound to - change the PropertyChanged to "CurrentArtist" and you'll see it update properly.
You are not raising the PropertyChanged event, what you need is:
public sealed class DeviceManager : INotifyPropertyChanged
{
// Singleton members omitted
public IPlayer Player
{
get { return player; }
set
{
this.player = value;
OnPropertyChanged(this, new PropertyChangedEventArgs("Player"));
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(sender, e);
}
}
#endregion
}
How does the UI know when you change the Player property? From that code it does not look like it raises PropertyChanged to me. Can you post a complete working sample of the problem? Otherwise we're forced to just guess.