What Is a Functional Dependency?

Windows Presentation Foundation (WPF) provides a set of services that can be used to extend the functionality of the common language runtime (CLR) attribute. These services are often collectively referred to as the WPF attribute system. Properties supported by the WPF property system are called dependency properties. A dependency property is a property that can have no value of its own and can obtain a value from a data source by using Binding (in popular terms, it depends on other properties).

Dependent property

Right!

Windows Presentation Foundation (WPF) provides a set of services that can be used to extend the functionality of the common language runtime (CLR) properties. These services are often collectively referred to as the WPF attribute system. Properties supported by the WPF property system are called dependency properties. A dependency property is a property that can have no value of its own and can obtain a value from a data source by using Binding (in popular terms, it depends on other properties).

1. Dependency attributes support CLR attributes

2. The purpose of dependency attributes is to provide a way to calculate attribute values based on other input values. These other inputs can include system attributes (such as themes and user preferences), real-time attribute determination mechanisms (such as data binding and animation / dashboards), reuse templates (such as resources and styles), or Parent-child relationship to expose the value. In addition, you can implement dependency properties to provide independent validation, default values, callbacks that monitor changes to other properties, and a system that can force property values to be specified based on possible runtime information. Derived classes can also change some specific characteristics of existing properties by overriding dependency property metadata instead of overriding the actual implementation of existing properties or creating new properties. ^[1]

     // Depending on the property name MyTextProperty
    // Depending on the property identifier MyText
    publicstaticreadonlyDependencyPropertyMyTextProperty =
    DependencyProperty.Register ("MyText", typeof (string), typeof (MyTextBox));
   
    // CLR properties that depend on properties wrap publicstringMyText
    {
    get {return (string) GetValue (MyTextProperty);}
    set {SetValue (MyTextProperty, value);}
    } 

   Register method parameter description

   name	The name of the dependency object to be registered.
   propertyType	The type of the attribute.
   ownerType	The owner type of the dependency object is being registered.
   typeMetadata	Attribute metadata for dependency objects.
   validateValueCallback	A reference to the callback, in addition to the typical type validation, the reference should perform any custom validation of the value of the dependency object.

   Dependent property resource

   Dependency property values can be set by referencing resources.

     <Window.Resources>
    <!-Resources->
    <sys: Stringx: Key = "text"> text_Resources </ sys: String>
    </Window.Resources>
    <Grid>
    <!-Text property reference resource->
    <MyTextBox: MyTextBoxx: Name = "myTextBox" HorizontalAlignment = "Left" Height = "44"
    Margin = "70,81,0,0" TextWrapping = "Wrap" VerticalAlignment = "Top" Width = "213"
    Text = "{DynamicResourcetext}" />
    </ Grid> 

   Dependent property data binding

   Binding notes: (1) the binding must specify the data context DataContext;

   (2) The binding source must be an attribute, and the variable is invalid;

   (3) The binding source must be public.

   (4) If the binding target's dependent property needs to follow changes when the binding source changes, the binding source must inherit the INotifyPropertyChanged interface.

   Example (the TextBox.Text dependency property is bound to the TextForBinding property in the MainWindow class):

   public string TextForBinding {get; set;}

   Writing the inherited INotifyPropertyChanged interface:

   public partial class MainWindow: Window, INotifyPropertyChanged

   {

   public string TextForBinding {get; set;}

   public event PropertyChangedEventHandler PropertyChanged;

   private void OnPropertyChanged (string info)

   {

   PropertyChangedEventHandler handler = PropertyChanged;

   if (handler! = null)

   {

   handler (this, new PropertyChangedEventArgs (info));

   }

   }

   }

   XAML:

   Text = "{Binding TextForBinding}" style

   Example (write a red foreground color style and quote):

   Writing style:

   <Window.Resources> <!-Resources->

   <sys: String x: Key = "text"> text_Resources </ sys: String>

   <Style x: Key = "MyStyle" TargetType = "MyTextBox: MyTextBox">

   <Setter Property = "Foreground" Value = "Red" />

   </ Style>

   </Window.Resources>

   Reference style

   Style = "{DynamicResource MyStyle} Animation metadata override property values inherit WPF designer integration dependency property priority

   The highest priority will be listed first, in the following order:

   1. Property system coercion.

   2. Active animation or animation with Hold behavior. In order to get any useful effect, the animation of the property must take precedence over the base (unanimated) value, even if the value is set locally.

   3. Local value. Local values can be set through the convenience of "wrapper" attributes, which is also equivalent to setting attributes or attribute elements in XAML, or calling the SetValue API with attributes of a specific instance. If you use bindings or resources to set local values, each value is applied in the order of precedence of directly set values.

   4. TemplatedParent template property. If the element was created as part of a template (ControlTemplate or DataTemplate), it has a TemplatedParent. In the template, the following priorities apply:

   1. Trigger from TemplatedParent template.

   2. TemplatedParent The set of attributes in the template. (Usually set via XAML attributes.)

   5. Implicit style. Applies only to the Style property. The Style property is populated by any style resource with a key that matches its type. The style resource must exist in the page or application; finding implicit style resources does not go into the theme.

   6. Style trigger. From a trigger in a style on a page or application. (These styles can be explicit or implicit, but not from the lower-priority default styles.)

   7. Template trigger. Any trigger from a template in a style or a template applied directly.

   8. Style Setter. The value from the setter in the style of the page or application.

   9. The default (theme) style. In the default style, they are applied in the following order of priority:

   1. Activity trigger in theme style.

   2. Setter in theme style.

   10. inherit. There are several dependency properties that inherit values from parent elements to child elements, so there is no need to set these properties specifically on each element in the application.

   11. The default value from the dependency property metadata. Any given dependency property has a default value, which is determined by the property system registration for that particular property. Also, derived classes that inherit dependency properties have the option to override this metadata (including default values) by type. Because inheritance is checked before the default value, for inherited properties, the default value of the parent element takes precedence over the child element. Therefore, if no inheritable property is set anywhere, the default value specified in the root or parent element will be used instead of the child element's default value.