自定義WPF UI控件，並實現binding屬性

<UserControl x:Class="CostWPF.UserControls.LabelComboBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d" 
             d:DesignHeight="31.05" d:DesignWidth="360" x:Name="labelComboBox">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="30*"></ColumnDefinition>
            <ColumnDefinition Width="70*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <TextBlock TextWrapping="Wrap" Text="{Binding Label, ElementName=labelComboBox}" VerticalAlignment="Center"   TextAlignment="Right"></TextBlock>
        <ComboBox Grid.Column="1" Name="CBB_Content" ItemsSource="{Binding Items, ElementName=labelComboBox}" VerticalAlignment="Center" SelectedItem="{Binding Value, ElementName=labelComboBox}"   Margin="10,0,0,0">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Text, ElementName=labelComboBox}" />
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
    </Grid>
</UserControl>

        public static readonly DependencyProperty TextTProperty = DependencyProperty.Register("Label", typeof(string), typeof(LabelComboBox));
        public string Label
        {
            get { return (string)GetValue(TextTProperty); }
            set
            {
                SetValue(TextTProperty, value);
            }
        }



        public static readonly DependencyProperty ValueProperty =
            DependencyProperty.Register(
                "Value", typeof(KeyText), typeof(LabelComboBox), new FrameworkPropertyMetadata(null) { BindsTwoWayByDefault = true });
        public KeyText Value
        {
            get { return GetValue(ValueProperty) as KeyText; }
            set
            {
                SetValue(ValueProperty, value);
            }
        }



        public static readonly DependencyProperty ItemsProperty =
            DependencyProperty.Register(
                "Items", typeof(List<KeyText>), typeof(LabelComboBox), new FrameworkPropertyMetadata(new List<KeyText>()) { BindsTwoWayByDefault = true });
        public List<KeyText> Items
        {
            get { return GetValue(ItemsProperty) as List<KeyText>; }
            set
            {
                SetValue(ItemsProperty, value);
            }
        }

重點：
1、在UserControl上，加一個x:Name, 並在下邊的所有綁定裏，添加, ElementName=x:Name
2、在後臺代碼裏，需要使用DependencyProperty來定義屬性

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參考：
https://www.cnblogs.com/mq0036/p/12356454.html