I need to add logic of a property setter.
For example, I have a property named "CurrentTab":
private WorkspaceViewModel _currentTab;
public WorkspaceViewModel CurrentTab
{
get
{
return _currentTab;
}
set
{
_currentTab = value;
OnPropertyChanged("CurrentTab");
}
}
This is all good and works, but I want to be able to just define it like this:
public WorkspaceViewModel CurrentTab { get; set; }
So that the system automatically performs the OnPropertyChanged() function for the property name after the setter has run without me adding any specific code.
How to identify which properties need to follow this logic is no problem, I just need to find a way how to actually do it.
I want to make this simpler because I'll be having quite a lot of those kind of properties and I'd like to keep it clean.
Is there a way?
Any help is much appreciated!
Take a look: Fody. There is an add-in for INotifyPropertyChange: github
It is manipulating IL code while building the solution.
You need only to add attribute to view model:
[ImplementPropertyChanged]
public class Person
{
public string GivenNames { get; set; }
public string FamilyName { get; set; }
public string FullName
{
get
{
return string.Format("{0} {1}", GivenNames, FamilyName);
}
}
}
When code gets compiled:
public class Person : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
string givenNames;
public string GivenNames
{
get { return givenNames; }
set
{
if (value != givenNames)
{
givenNames = value;
OnPropertyChanged("GivenNames");
OnPropertyChanged("FullName");
}
}
}
string familyName;
public string FamilyName
{
get { return familyName; }
set
{
if (value != familyName)
{
familyName = value;
OnPropertyChanged("FamilyName");
OnPropertyChanged("FullName");
}
}
}
public string FullName
{
get
{
return string.Format("{0} {1}", GivenNames, FamilyName);
}
}
public virtual void OnPropertyChanged(string propertyName)
{
var propertyChanged = PropertyChanged;
if (propertyChanged != null)
{
propertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
This can be achieved using PostSharp, which is an Aspect Oriented Programming approach:
In computing, aspect-oriented programming (AOP) is a programming
paradigm that aims to increase modularity by allowing the separation
of cross-cutting concerns. AOP forms a basis for aspect-oriented
software development.
You can implement this using an Aspect called InstanceLevelAspect:
/// <summary>
/// Aspect that, when apply on a class, fully implements the interface
/// <see cref="INotifyPropertyChanged"/> into that class, and overrides all properties to
/// that they raise the event <see cref="INotifyPropertyChanged.PropertyChanged"/>.
/// </summary>
[Serializable]
[IntroduceInterface(typeof(INotifyPropertyChanged),
OverrideAction = InterfaceOverrideAction.Ignore)]
[MulticastAttributeUsage(MulticastTargets.Class | MulticastTargets.Property,
Inheritance = MulticastInheritance.Strict)]
public sealed class NotifyPropertyChangedAttribute : InstanceLevelAspect,
INotifyPropertyChanged
{
/// <summary>
/// Field bound at runtime to a delegate of the method OnPropertyChanged
/// </summary>
[ImportMember("OnPropertyChanged", IsRequired = false)]
public Action<string> OnPropertyChangedMethod;
/// <summary>
/// Method introduced in the target type (unless it is already present);
/// raises the <see cref="PropertyChanged"/> event.
/// </summary>
/// <param name="propertyName">Name of the property.</param>
[IntroduceMember(Visibility = Visibility.Family, IsVirtual = true,
OverrideAction = MemberOverrideAction.Ignore)]
public void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this.Instance,
new PropertyChangedEventArgs(propertyName));
}
}
/// <summary>
/// Event introduced in the target type (unless it is already present);
/// raised whenever a property has changed.
/// </summary>
[IntroduceMember(OverrideAction = MemberOverrideAction.Ignore)]
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Method intercepting any call to a property setter.
/// </summary>
/// <param name="args">Aspect arguments.</param>
[OnLocationSetValueAdvice,
MulticastPointcut( Targets = MulticastTargets.Property,
Attributes = MulticastAttributes.Instance)]
public void OnPropertySet(LocationInterceptionArgs args)
{
// Don't go further if the new value is equal to the old one.
// (Possibly use object.Equals here).
if (args.Value == args.GetCurrentValue())
{
return;
}
// Actually sets the value.
args.ProceedSetValue();
// Invoke method OnPropertyChanged (our, the base one, or the overridden one).
this.OnPropertyChangedMethod.Invoke(args.Location.Name);
}
}
Then, use it on your property like this:
[NotifyPropertyChanged]
public WorkspaceViewModel CurrentTab { get; set; }
This attirubte can also be applied at the class level, if you want all your properties to implement NotifyPropertyChanged. More on the example can be found here
Related
I have a small WPF application and I'm beginning to learn the MVVM Data Binding pattern. I have an empty textBox and I have bound it to "FirstName" however when I run my code it's not updating. I have an ObservableObject class which inherits from the INotifyPropertyChanged class to check if the property has been updated. When I run the code the property does take the correct value however the UI never updates.
My code is as follows
MainWindow.xaml
<TextBox Grid.Row="0" Grid.Column="1" Text="{Binding FirstName}" VerticalAlignment="Center" HorizontalAlignment="Left" TextWrapping="Wrap" FontSize="16" Margin="20,20,0,20" Width="132"></TextBox>
Main Windows.xaml.cs
public MainWindow()
{
InitializeComponent();
this.DataContext = new MainViewModel();
}
Person.cs
class Person:ObservableObject
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set
{
_firstName = value;
RaisePropertyChanged("FirstName");
}
}
}
MainViewModel.cs
class MainViewModel:ObservableObject
{
List<Person> pList = new List<Person>();
public MainViewModel()
{
pList = new List<Person>()
{
new Person() {FirstName="Craig"}
};
Init();
}
public void Init()
{
var li = pList.FirstOrDefault();
}
}
OnservableObject.cs
[Serializable]
public abstract class ObservableObject : INotifyPropertyChanged, IDisposable
{
#region Constructor
protected ObservableObject()
{
}
#endregion Constructor
#region DisplayName
/// <summary>
/// Returns the user-friendly name of this object.
/// Child classes can set this property to a new value,
/// or override it to determine the value on-demand.
/// </summary>
public virtual string DisplayName { get; protected set; }
#endregion DisplayName
#region INotifyPropertyChanged Members
[field: NonSerialized]
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
{
this.PropertyChanged?.Invoke(this, e);
}
protected void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpresssion)
{
var propertyName = PropertySupport.ExtractPropertyName(propertyExpresssion);
this.RaisePropertyChanged(propertyName);
}
protected void RaisePropertyChanged(String propertyName)
{
VerifyPropertyName(propertyName);
OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
}
#endregion INotifyPropertyChanged Members
#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 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 IDisposable Members
/// <summary>
/// Invoked when this object is being removed from the application
/// and will be subject to garbage collection.
/// </summary>
public void Dispose()
{
this.OnDispose();
}
/// <summary>
/// Child classes can override this method to perform
/// clean-up logic, such as removing event handlers.
/// </summary>
protected virtual void OnDispose()
{
}
/// <summary>
/// Useful for ensuring that ViewModel objects are properly garbage collected.
/// </summary>
~ObservableObject()
{
string msg = string.Format("{0} ({1}) ({2}) Finalized", this.GetType().Name, this.DisplayName, this.GetHashCode());
Debug.WriteLine(msg);
}
#endregion IDisposable Members
}
PropertySupport.cs
public static class PropertySupport
{
public static String ExtractPropertyName<T>(Expression<Func<T>> propertyExpresssion)
{
if (propertyExpresssion == null)
{
throw new ArgumentNullException("propertyExpresssion");
}
var memberExpression = propertyExpresssion.Body as MemberExpression;
if (memberExpression == null)
{
throw new ArgumentException("The expression is not a member access expression.", "propertyExpresssion");
}
var property = memberExpression.Member as PropertyInfo;
if (property == null)
{
throw new ArgumentException("The member access expression does not access a property.", "propertyExpresssion");
}
var getMethod = property.GetGetMethod(true);
if (getMethod.IsStatic)
{
throw new ArgumentException("The referenced property is a static property.", "propertyExpresssion");
}
return memberExpression.Member.Name;
}
}
You should make a property CurrentPerson, or something like this, in your MainViewModel. CurrentPerson should be e.g. the first entry of your pList. Then you can bind to CurrentPerson.FirstName.
The MainViewModel has no property called FirstName. In fact, it has no property at all.
If you define pList as a public property:
class MainViewModel : ObservableObject
{
public List<Person> pList { get; }
public MainViewModel()
{
pList = new List<Person>()
{
new Person() {FirstName="Craig"}
};
}
}
...you can bind to the first Person object in the List<Person> like this:
<TextBox Grid.Row="0" Grid.Column="1" Text="{Binding pList[0].FirstName}" />
Alternatively, you could add a Person property that returns the value of pList.FirstOrDefault() to the MainViewModel class and bind to this one in your XAML.
But you can only bind to public properties. You cannot bind to fields.
You are trying to bind the Model's property directly to the UI.
Think what you are going to bind to the TextBox. You are having a list of Person, from which you may bind selected person's FirstName property to the TextBox. In that sense, create a SelectedPerson property in ViewModel and bind the SelectedPerson.FirstName to the TextBox which would work.
Add the below property to your viewmodel
private Person _selectedPerson;
public Person SelectedPerson
{
get { return _selectedPerson; }
set
{
_selectedPerson= value;
RaisePropertyChanged("SelectedPerson");
}
}
And try to bind as follows in XAML
<TextBox Grid.Row="0" Grid.Column="1" Text="{Binding SelectedPerson.FirstName}" VerticalAlignment="Center" HorizontalAlignment="Left" TextWrapping="Wrap" FontSize="16" Margin="20,20,0,20" Width="132"></TextBox>
The answer to this question has been edited to say that in C# 6.0, INotifyPropertyChanged can be implemented with the following OnPropertyChanged procedure:
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
However, it isn't clear from that answer what the corresponding property definition should be. What does a complete implementation of INotifyPropertyChanged look like in C# 6.0 when this construction is used?
After incorporating the various changes, the code will look like this. I've highlighted with comments the parts that changed and how each one helps
public class Data : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
//C# 6 null-safe operator. No need to check for event listeners
//If there are no listeners, this will be a noop
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
// C# 5 - CallMemberName means we don't need to pass the property's name
protected bool SetField<T>(ref T field, T value,
[CallerMemberName] string propertyName = null)
{
if (EqualityComparer<T>.Default.Equals(field, value))
return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
private string name;
public string Name
{
get { return name; }
//C# 5 no need to pass the property name anymore
set { SetField(ref name, value); }
}
}
I use the same logic in my project. I have a base class for all view models in my app:
using System.ComponentModel;
using System.Runtime.CompilerServices;
public class PropertyChangedBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Every view model inherits from this class. Now, in the setter of each property I just need to call OnPropertyChanged().
public class EveryViewModel : PropertyChangedBase
{
private bool initialized;
public bool Initialized
{
get
{
return initialized;
}
set
{
if (initialized != value)
{
initialized = value;
OnPropertyChanged();
}
}
}
Why does it work?
[CallerMemberName] is automatically populated by the compiler with the name of the member who calls this function. When we call OnPropertyChanged from Initialized, the compiler puts nameof(Initialized) as the parameter to OnPropertyChanged
Another important detail to keep in mind
The framework requires that PropertyChanged and all properties that you're binding to are public.
I know this question is old, but here is my implementation
Bindable uses a dictionary as a property store. It's easy enough to add the necessary overloads for a subclass to manage its own backing field using ref parameters.
No magic string
No reflection
Can be improved to suppress the default dictionary lookup
The code:
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));
}
}
used like this
public class Item : Bindable
{
public Guid Id { get { return Get<Guid>(); } set { Set<Guid>(value); } }
}
Say I have a Logger class, a LoggerViewModel class and a MainWindow with a TextBox. The Logger class is a thread-safe singleton, so I have only an instance of it in the application domain.
public sealed class Logger : INotifyPropertyChanged
{
private static readonly Logger _Instance = new Logger();
private static readonly object _SyncLock = new object();
private static List<LogEntry> _Data = new List<LogEntry>();
/// <summary>
///
/// </summary>
private Logger() { ; }
/// <summary>
///
/// </summary>
public static Logger Instance
{
get { return _Instance; }
}
/// <summary>
///
/// </summary>
/// <param name="entry"></param>
public void Write(LogEntry entry)
{
lock (_SyncLock)
{
_Data.Add(entry);
}
this.RaiseNotifyPropertyChanged("Entries");
}
/// <summary>
///
/// </summary>
/// <param name="component"></param>
/// <param name="message"></param>
public void Write(string component, string message)
{
LogEntry entry = LogEntry.Create(component, message);
Write(entry);
}
/// <summary>
///
/// </summary>
public IList<LogEntry> Entries
{
get
{
lock (_SyncLock)
{
return new ReadOnlyCollection<LogEntry>(_Data);
}
}
}
/// <summary>
///
/// </summary>
/// <param name="property"></param>
private void RaiseNotifyPropertyChanged(string property)
{
var handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(property));
}
}
/// <summary>
///
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
}
The Logger unique instance is updated by more thread while the application is running, so I would update the TextBox on the MainWindow whenever the model (that is the Logger singleton class) changes.
How to connect the Model and the ViewModel between them? I emphasize that the Model is changed by only a few application thread, so it is read-only from the point of view of UI.
I provided the LoggerText property within the LoggerViewModel class, since I thought the following working mechanism.
1. When the Model (the Logger instance) changes, it notifies the ViewModel.
2. The ViewModel receives the notify by the Model and create a new string containing all the messages from the logger.
3. The ViewModel notifies the View.
public class LoggerViewModel : INotifyPropertyChanged
{
Logger _LoggerModel;
/// <summary>
///
/// </summary>
public LoggerViewModel()
{
_LoggerModel = Logger.Instance;
}
/// <summary>
///
/// </summary>
public string LoggerText
{
get
{
string text = "";
List<LogEntry> entries = new List<LogEntry>(_LoggerModel.Entries);
foreach (LogEntry entry in entries)
{
text += entry.ToString();
text += "\n";
}
return text;
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
// take a copy to prevent thread issues
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
How the ViewModel can intercept the notifications sent by the Model?
First of all I do not like that you are using a singleton. When using the singleton pattern you are making it hard on yourself when testing or reusing your view controllers. I would instead inject the Logger dependency into your LoggerViewModel class.
Aside from that one way to solve your problem is to register a handler for the PropertyChanged event on your Logger and build the text when the event fires for the Entries property.
In LoggerViewModel you would then add a property handler and update the LoggerText property as needed.
public LoggerViewModel(Logger loggerModel /* Dependency injection*/)
{
_LoggerModel = loggerModel;
_LoggerModel.PropertyChanged += this.LoggerModel_PropertyChanged;
}
private void LoggerModel_PropertyChanged(object sender, PropertyChangedEventArgs args)
{
if (args.PropertyName == "Entries")
{
StringBuilder text = new StringBuilder(); // Use StringBuilder for performance
List<LogEntry> entries = new List<LogEntry>(_LoggerModel.Entries);
foreach (LogEntry entry in entries)
{
text.AppendLine(entry.ToString());
}
this.LoggerText = text.ToString();
}
}
private string _loggerText;
public string LoggerText
{
set
{
_loggerText = value;
RaisePropertyChanged("LoggerText");
}
get
{
return _loggerText;
}
}
Disclaimer: The above code is written without a compiler.
I'm binding an UltraTree control (version 10.3) to a custom data source, like so:
public void Populate(List<FilterDimension> data)
{
DataBindings.Clear();
DataSource = data;
Nodes[0].DataColumnSetResolved.NodeTextColumn = Nodes[0].DataColumnSetResolved.Columns["DisplayText"];
}
My expectation is that changing the DisplayText property on any of the bound FilterDimension objects will cause the UltraTree node's text to update. In reality, the text in the tree does not update, and the PropertyChanged event remains null indicating that the UltraTree doesn't even listen for this notification. How do I get the UltraTree to listen for property changes in FilterDimension?
Here's the relevant code from FilterDimension:
internal class FilterDimension : INotifyPropertyChanged
{
private string _displayText = null;
private string _name = null;
private BindingList<string> _values = new BindingList<string>();
/// <summary>
/// Gets or sets the display friendly name.
/// </summary>
public string Name
{
get { return _name; }
set
{
_name = value;
FirePropertyChangedNotification("Name");
if (_displayText == null) { FirePropertyChangedNotification("DisplayText"); }
}
}
/// <summary>
/// Gets or sets the display text that is used in TreeView nodes. When null, uses the Name.
/// </summary>
public string DisplayText
{
get { return _displayText ?? Name; }
set { _displayText = value; FirePropertyChangedNotification("DisplayText"); }
}
/// <summary>
/// Gets a read/write list of values. Is never null.
/// </summary>
public BindingList<string> Values
{
get { return _values; }
set { _values = value ?? new BindingList<string>(); }
}
#region Events
public event PropertyChangedEventHandler PropertyChanged;
protected void FirePropertyChangedNotification(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
It turns out that all I needed to do was change to BindingList<FilterDimension> instead of List<FilterDimension... I completely missed that the control expects notifications to bubble up from the list.
The mainpage:
MainPage.xaml
<Canvas x:Name="LayoutRoot" Background="White">
</Canvas>
MainPage.xaml.cs
List<Usol> list = new List<Usol>();
for (int i = 0; i < 10; i++)
{
var element = new Usol();
list.Add(element);
Canvas.SetTop(element, i * 25);
LayoutRoot.Children.Add(list[i]);
}
foreach (var item in list)
{
item.context.name = "Varken";
}
A usercontrol
Usol.xaml
<Grid x:Name="LayoutRoot" Background="White">
<TextBlock Text="{Binding Name}" />
</Grid>
Usol.xaml.cs
public Context context;
public Usol()
{
InitializeComponent();
context = new Context();
this.DataContext = context;
}
A class
Context.cs
public class Context : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#region Fields
/// <summary>
/// Field Declaration for the <see cref="Name"/>
/// </summary>
private string name;
#endregion
#region Properties
/// <summary>
/// Gets or Sets the Name
/// </summary>
public string Name
{
get { return name; }
set
{
if (this.name != value)
{
this.name = value;
OnPropertyChanged("Name");
}
}
}
#endregion
}
Situation
I have created this small test application to copy a problem I have in a bigger application. It works about the same way (not exactly, but close enough).
It adds several custom made usercontrols and each get a own instance of a datacontext class.
However, none of the properties are willing to update themselfs due to a empty PropertyChangedEventHandler.
Question
Why is public event PropertyChangedEventHandler PropertyChanged; always null?
Context.cs needs to implement INotifyPropertyChanged interface. Are you doing that?
Edit: Post your update.
I have generally seen this kind of problem when programmers create "two" instances of Model/ViewModel. While you attach one instance with View, it's always the other one that gets update (which ofcourse will have a null PropertyChanged subscribers). Thus, you must make sure that your view is using the same instance as being updated at other parts.
Hope my point is clear.
Your code is wrong,
OnPropertyChanged("Name"); <-- should update "name" not "Name"
You are firing event saying that "Name" is changed, but name of property is "name", C# and binding are case sensitive.
Change it to,
#region Fields
/// <summary>
/// Field Declaration for the <see cref="name"/>
/// </summary>
private string _Name;
#endregion
#region Properties
/// <summary>
/// Gets or Sets the name
/// </summary>
public string Name
{
get { return _Name; }
set
{
if (this._Name != value)
{
this._Name = value;
OnPropertyChanged("Name");
}
}
}
#endregion
From C# 6 on wards, please use nameof() keyword...
#region Fields
/// <summary>
/// Field Declaration for the <see cref="name"/>
/// </summary>
private string _Name;
#endregion
#region Properties
/// <summary>
/// Gets or Sets the name
/// </summary>
public string Name
{
get { return _Name; }
set
{
if (this._Name != value)
{
this._Name = value;
OnPropertyChanged(nameof(Name));
}
}
}
#endregion