WPF自定义Button用户控件绑定RelayCommand无响应求助

我开发了一款包含图标、自定义文本块的Button用户控件，通过DependencyProperty传递Command，但点击时Command无响应。相同的RelayCommand代码在普通Button上可正常执行。基于.NET Framework 4.8.1的测试项目代码如下：

项目代码 #

MainWindow.xaml #

<Window x:Class="wpfuitest1.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:local="clr-namespace:wpfuitest1"
        xmlns:userControl="clr-namespace:wpfuitest1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <StackPanel>
            <userControl:boton Command="{Binding TestCommand}"
                               ButtonContent="Non working Command button"/>
            
            <Button Content="Working Command button"
                    Command="{Binding TestCommand}"></Button>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs #

using System.Windows;
namespace wpfuitest1
{
    public partial class MainWindow : Window
    {
        private readonly VM vm = new VM();
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = vm;
        }
    }
}

VM.cs #

using System;
namespace wpfuitest1
{
    internal class VM
    {
        public RelayCommand TestCommand => new RelayCommand(execute => Test(), canExecute => { return true; });
        public void Test()
        {
            Console.WriteLine("test");
        }
    }
}

RelayCommand.cs #

using System;
using System.Windows.Input;

namespace wpfuitest1
{
    internal class RelayCommand : ICommand
    {
        private Action<object> execute;
        private Func<object, bool> canExecute;

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
        {
            this.execute = execute;
            this.canExecute = canExecute;
        }

        public bool CanExecute(object parameter = null)
        {
            return canExecute == null | canExecute(parameter);
        }

        public void Execute(object parameter)
        {
            execute(parameter);
        }
    }
}

boton.xaml（自定义用户控件） #

<UserControl x:Class="wpfuitest1.boton"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:wpfuitest1"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">

    <Button Style="{DynamicResource ButtonStyle1}" Content="{Binding ButtonContent}"
            Command="{Binding Command}">
    </Button>
</UserControl>

boton.xaml.cs #

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

namespace wpfuitest1
{
    public partial class boton : UserControl
    {
        public boton()
        {
            InitializeComponent();
            this.DataContext = this;
        }

        public string ButtonContent
        {
            get { return (string)GetValue(ButtonContentProperty); }
            set { SetValue(ButtonContentProperty, value); }
        }
        public static readonly DependencyProperty ButtonContentProperty =
            DependencyProperty.Register("ButtonContent", typeof(string), typeof(boton), new PropertyMetadata(""));


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

        public static readonly DependencyProperty CommandProperty = DependencyProperty.Register(
            "Command", typeof(ICommand), typeof(boton), new PropertyMetadata(null));
    }
}

问题原因 #

核心问题出在自定义控件boton的构造函数中设置了this.DataContext = this;，导致两个关键错误：

1. 外部使用userControl:boton Command="{Binding TestCommand}"时，绑定的数据源变成了boton实例本身，而非父级的VM，因此TestCommand无法正确赋值给控件的Command依赖属性。
2. 内部Button的Command="{Binding Command}"虽然能找到控件的Command属性，但由于外部绑定失效，该属性值始终为null，点击自然无响应。

解决方案 #

步骤1：移除自定义控件的DataContext赋值 #

删除boton.xaml.cs构造函数中的this.DataContext = this;代码，让控件继承父级的DataContext（即MainWindow的VM），确保外部的Command绑定能正确关联到VM的TestCommand。

步骤2：修改内部控件的绑定方式 #

使用ElementName或RelativeSource让内部Button直接绑定到自定义控件的依赖属性，避免DataContext冲突。

修改后的boton.xaml（使用ElementName）

<UserControl x:Class="wpfuitest1.boton"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:wpfuitest1"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800"
             x:Name="RootControl">

    <Button Style="{DynamicResource ButtonStyle1}" 
            Content="{Binding ButtonContent, ElementName=RootControl}"
            Command="{Binding Command, ElementName=RootControl}">
    </Button>
</UserControl>

修改后的boton.xaml.cs

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

namespace wpfuitest1
{
    public partial class boton : UserControl
    {
        public boton()
        {
            InitializeComponent();
        }

        public string ButtonContent
        {
            get { return (string)GetValue(ButtonContentProperty); }
            set { SetValue(ButtonContentProperty, value); }
        }
        public static readonly DependencyProperty ButtonContentProperty =
            DependencyProperty.Register("ButtonContent", typeof(string), typeof(boton), new PropertyMetadata(""));


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

        public static readonly DependencyProperty CommandProperty = DependencyProperty.Register(
            "Command", typeof(ICommand), typeof(boton), new PropertyMetadata(null));
    }
}

替代绑定方式（使用RelativeSource） #

如果不想用ElementName，也可以用RelativeSource指定父级UserControl：

Content="{Binding ButtonContent, RelativeSource={RelativeSource AncestorType=UserControl}}"
Command="{Binding Command, RelativeSource={RelativeSource AncestorType=UserControl}}"

内容的提问来源于stack exchange，提问作者Flacuchentxox