用户控件库中的依赖项属性始终为空

Question

所以我得到了此控件：

CharacterMapControl.xaml：

<UserControl x:Class="CharacterMap.CharacterMapControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:CharacterMap">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="350"/>
        </Grid.RowDefinitions>
        <StackPanel Grid.Row="0" Orientation="Horizontal">
            <TextBlock Text=""></TextBlock>
        </StackPanel>
    </Grid>


</UserControl>

然后打开CharacterMapControl.xaml.cs：

using System.Windows;
using System.Windows.Controls;

namespace CharacterMap
{
    /// <summary>
    /// Interaction logic for CharacterMapControl.xaml
    /// </summary>
    ///     
    public partial class CharacterMapControl : UserControl 
    {
        public static readonly DependencyProperty FilepathProperty = DependencyProperty.Register("Filepath", typeof(string), typeof(CharacterMapControl));
        public string Filepath
        {
            get { return (string)GetValue(FilepathProperty); }
            set { SetValue(FilepathProperty, value); }
        }



        public CharacterMapControl()
        {
            InitializeComponent();
        }
    }
}

这在.NET Core的WPF用户控件库中。

然后我添加了一个新的WPF App .NET Core项目并编辑了MainWindow.xaml，如下所示：

<Window x:Class="WPF_Control_Tester.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:charactermap="clr-namespace:CharacterMap;assembly=CharacterMap"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <charactermap:CharacterMapControl Filepath="D:\\repos\\WpfProjects\\latinchars.xml"></charactermap:CharacterMapControl>
    </Grid>
</Window>

嗯-现在CharacterMapControl.xaml.cs中的Filepath始终为null。我不明白为什么。它绑定正确，应该映射到我在MainWindow中添加的Filepath还是？

Answer 1

构造CharacterMapControl时，依赖项属性值为null，因为在定义依赖项属性时未指定默认值。

构造控件CharacterMapControl之后不久，将引发已加载的事件，这时依赖项属性将具有初始化的值。

如下修改构造函数将有助于进一步了解。

        public CharacterMapControl()
        {
            InitializeComponent();

            var y = GetValue(FilepathProperty);
            Console.WriteLine(y);

            this.Loaded += (sender, args) =>
            {
                var x = GetValue(FilepathProperty);
                Console.WriteLine(x);
            };
        }

Answer 2

您尚未将TextBlock的Text属性绑定到任何东西。

当我尝试您的代码时，我添加了绑定：

        <TextBlock Text="{Binding Filepath, RelativeSource={RelativeSource AncestorType=UserControl}}"/>

哪个作品