Custom ReadOnlyProperty【PluraSight】

Limited functionality:

• Not settable
• No data binding
• No validation
• No animation
• No Inheritance

When to use?

• Used for state determination(Defined the style for the control, some visiable property like fore/background will change when mouse movehover)
• Used as a property trigger(由这个readonly property change，来change control's states)

要求： 我们有一个button，和一个read-only property来track button is been clicked的状态，如果被clicked的话，这个property变为true，我们change button的background

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace CustomControlLib
{
    public class MyCustomControl : Control
    {
        static MyCustomControl()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(MyCustomControl), new FrameworkPropertyMetadata(typeof(MyCustomControl)));
        }
        private static readonly DependencyPropertyKey HasBeenClickedPropertyKey = DependencyProperty.RegisterReadOnly("HasBeenClicked",
            typeof(bool), typeof(MyCustomControl), new PropertyMetadata(false));
        public static readonly DependencyProperty HasBeenClickedProperty = HasBeenClickedPropertyKey.DependencyProperty;
        //When you create the DependencyPropertyKey it will automaticly create the DependencyProperty for you

        public bool HasBeenClicked  //注意这里的wrapper的名字要和register时给的""里的名字一致
        {
            get { return (bool)GetValue(HasBeenClickedProperty); }  //因为做的是 readonly property，所以只有getter
        }

        public override void OnApplyTemplate()  //override OnApplyTemplate
        {
            base.OnApplyTemplate();
            
            //demo purposes only, check for previous instances and remove handler first
            var button = GetTemplateChild("PART_Button") as Button; //call 前台的x:Name
            if (button != null)
                button.Click += Button_Click;   //hock OnApplyTemplate() 去instantiate 一个按钮被点击的Event Handler

        }

        void Button_Click(object sender, RoutedEventArgs e)
        {
            SetValue(HasBeenClickedPropertyKey, true);  //其他继承类若要用这个DependencyPropertyKey，吧private改成protect或者internal
            //接下来要做的事当这个button被按后我们要set HasBeenClicked（ReadOnly）
            //不可以set HasBeenClicked只可以用SetValue找HasBeenClickedPropertyKey
        }
    }
}

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:CustomControlLib">


    <Style TargetType="{x:Type local:MyCustomControl}">
        <Setter Property="Margin" Value="50" />
        <Setter Property="Background" Value="Gray" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:MyCustomControl}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">

                        <Button x:Name="PART_Button"
                                Background="{TemplateBinding Background}"
                                Content="Click Me" />

                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="HasBeenClicked" Value="true">
                            <Setter Property="Background" Value="Green" />
                        </Trigger>

                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

<Window x:Class="CustomControlDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:cc="clr-namespace:CustomControlLib;assembly=CustomControlLib"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <cc:MyCustomControl />
    </Grid>
</Window>