Avalonia窗体中如何强制让TextBox获取键盘输入焦点

我有一个仅包含单个TextBox的Avalonia窗体，窗体显示时输入框不会自动获得键盘焦点，必须按Tab键才能输入内容，如何让TextBox在窗体显示时自动获取焦点？

原始AXAML代码 #

<Window xmlns="https://github.com/avaloniaui"
        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"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="SpaceDunyal.Forms.Window1"
        Title="MyWindow">
    <StackPanel Margin="10">
        <TextBox Name="MyInput" Watermark="Input your text"/>
    </StackPanel>
</Window>

原始C#代码 #

using Avalonia.Controls;

namespace SpaceDunyal.Forms
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            MyInput.Focus(); // 无效果
        }
    }
}

解决方案 #

方案1：通过AXAML直接设置初始焦点 #

在Window标签中添加FocusManager.FocusedElement属性，绑定到目标TextBox，无需编写C#代码即可实现自动聚焦：

<Window xmlns="https://github.com/avaloniaui"
        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"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="SpaceDunyal.Forms.Window1"
        Title="MyWindow"
        FocusManager.FocusedElement="{Binding ElementName=MyInput}">
    <StackPanel Margin="10">
        <TextBox Name="MyInput" Watermark="Input your text"/>
    </StackPanel>
</Window>

方案2：在窗体加载完成后调用Focus #

原始代码中MyInput.Focus()无效的核心原因是：Window构造函数执行时，控件还未完全加载到可视化树，布局也未完成，此时调用焦点设置不会生效。需要在窗体加载完成后再执行聚焦操作，有两种实现方式：

方式A：重写OnLoaded方法

using Avalonia.Controls;

namespace SpaceDunyal.Forms
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        protected override void OnLoaded(RoutedEventArgs e)
        {
            base.OnLoaded(e);
            MyInput.Focus();
        }
    }
}

方式B：订阅Loaded事件

using Avalonia.Controls;
using Avalonia.Interactivity;

namespace SpaceDunyal.Forms
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            Loaded += Window1_Loaded;
        }

        private void Window1_Loaded(object sender, RoutedEventArgs e)
        {
            MyInput.Focus();
        }
    }
}

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