Benutzer:MovGP0/WPF/Dependency Object

Dependency Object

WPF Property Requirements

Change Notifications
Default Values
Type Coercion
Data Binding
Attached Properties
Validation
Inheritance
Styling
Designer Support
Animation
etc.

Dependency Property

public sealed class Person : DependencyObject
{
    public static readonly DependencyProperty = 
        DependencyProperty.Register(nameof(Name), typeof(string), typeof(Person), 
            new UIPropertyMetadata(string.Empty));

    // helper that will not be used by WPF
    // may not contain additional logic 
    public string Name
    {
        get { return (string) GetValue(NameProperty); }
        set { SetValue(NameProperty, value); }
    }
}

with Change Notification

public sealed class Person : DependencyObject
{
    public static readonly DependencyProperty = 
        DependencyProperty.Register(nameof(Name), typeof(string), typeof(Person), 
            new UIPropertyMetadata(string.Empty, OnNameChanged));

    // every time the value changes 
    private static void OnNameChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        var target = (Person)source;
        var name = (string)e.NewValue; // e.OldValue, e.Property 
        target.OnNameChanged(name);
    }

    private void OnNameChanged(string Name)
    {
        // ...
    }

    public string Name
    {
        get { return (string) GetValue(NameProperty); }
        set { SetValue(NameProperty, value); }
    }
}

Attached Properties

<MyElement>
    <ChildElement MyElement.MyProperty="foo" />
</MyElement>

public sealed MyElement : DependencyObject // ie. Control
{
    public static readonly DependencyProperty MyPropertyProperty = 
        DependencyProperty.RegisterAttached("MyProperty", typeof(string), typeof(MyElement), 
            new UIPropertyMetadata(string.Empty));

    public static string GetMyProperty(DependencyObject obj)
    {
        return (string)obj.GetValue(MyPropertyProperty);
    }

    public static void SetMyProperty(DependencyObject obj, string value)
    {
        obj.SetValue(MyPropertyProperty, value);
    }
}

Inherited Properties

Properties that child elements get from their container
do not use for callbacks, because callback will be called on every child element

public sealed class Person : DependencyObject
{
    public static readonly DependencyProperty = 
        DependencyProperty.Register(nameof(Name), typeof(string), typeof(Person), 
            new UIPropertyMetadata(string.Empty, FrameworkPropertyMetadata.Inherits));

    public string Name
    {
        get { return (string) GetValue(NameProperty); }
        set { SetValue(NameProperty, value); }
    }
}

Readonly Properties

not setable
no data binding
no validation
no animation
no inheritance
used for state determination

private static readonly DependencyPropertyKey NamePropertyKey = 
    DependencyProperty.RegisterReadOnly(nameof(Name), typeof(MyControl), new PropertyMetadata(false));

private static readonly DependencyProperty NameProperty = 
    DependencyPropertyKey.DependencyProperty;

public string Name
{
    get { return (string)GetValue(NameProperty); }
}

// change value behind read-only property
public void ChangeName(string newName)
{
    SetValue(DependencyPropertyKey, newName); 
}

Collection Properties

Command Properties

User Control

<Grid>
    <Grid.DataContext>
        <local:MyControlViewModel />
    </Grid.DataContext>
    <Button Command="{Binding Command}" />
</Grid>

public class MyControl : UserControl
{
    public static readonly DependencyProperty CommandProperty = 
        DependencyProperty.Register(nameof(Command), typeof(ICommand), typeof(UserControl));

    public ICommand Command
    {
        get { return (ICommand)GetValue(CommandProperty);  }
        set { SetValue(CommandProperty, value); }
    }

    private void InvokeCommand()
    {
        Command?.Execute();
    }
}

Usage

public class MyViewModel
{
    public ICommand ViewModelCommand { get; } = new DelegateCommand(OnViewModelCommandExecute);

    private void OnViewModelCommandExecute()
    {
        // ...
    }
}

<UserControls:UserControl Command="{Binding ViewModelCommand}" />

Property Metadata

PropertyMetadata
- Default Value (Singleton)
- PropertyChangedCallback (react to value change)
- CoerceValueCallback (intercept and change the value for this control without changing the value)
FrameworkPropertyMetadata
- only inside a FrameworkElement (ie. Window, UserControl)
- FrameworkPropertyMetadataOptions
  - change or disable default binding mode
  - define inherited property
  - define if a change of this property affects arrangement, measurement or rendering of this control

Observing DependencyProperties^[1]

    public static class DependencyObjectExtensions
    {
        public static IObservable<EventArgs> Observe<T>(this T component, DependencyProperty dependencyProperty)
            where T:DependencyObject
        {
            return Observable.Create<EventArgs>(observer =>
            {
                EventHandler update = (sender, args) => observer.OnNext(args);
                var property = DependencyPropertyDescriptor.FromProperty(dependencyProperty, typeof(T));
                property.AddValueChanged(component, update);
                return Disposable.Create(() => property.RemoveValueChanged(component, update));
            });
        }
    }

    this.Observe(SomeProperty).Subscribe(args => ...);

Quellen

↑ Listen to changes of dependency property. In: StackOverflow. Abgerufen am 14. November 2016.

[so-1] Listen to changes of dependency property. In: StackOverflow. Abgerufen am 14. November 2016.

[1]

Benutzer:MovGP0/WPF/Dependency Object

Inhaltsverzeichnis

Dependency Object

WPF Property Requirements

Dependency Property

with Change Notification

Attached Properties

Inherited Properties

Readonly Properties

Collection Properties

Command Properties

Property Metadata

Observing DependencyProperties^[1]

Quellen

Navigationsmenü

Benutzer:MovGP0/WPF/Dependency Object

Dependency Object

WPF Property Requirements

Dependency Property

with Change Notification

Attached Properties

Inherited Properties

Readonly Properties

Collection Properties

Command Properties

Property Metadata

Observing DependencyProperties[1]

Quellen

Navigationsmenü

Suche

Observing DependencyProperties^[1]