Avalonia封装实现指定组件允许拖动的工具类

创建Avalonia的MVVM项目，命名DragDemo ，然后将项目的Nuget包更新到预览版

    <ItemGroup>
        <PackageReference Include="Avalonia" Version="11.0.0-preview5" />
        <PackageReference Include="Avalonia.Desktop" Version="11.0.0-preview5" />
        <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
        <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="11.0.0-preview5" />
        <PackageReference Include="Avalonia.ReactiveUI" Version="11.0.0-preview5" />
        <PackageReference Include="XamlNameReferenceGenerator" Version="1.5.1" />
    </ItemGroup>

更新完成以后ViewLocator和App.axaml会报错，

修改ViewLocator.cs为下面的代码

using System;
using Avalonia.Controls;
using Avalonia.Controls.Templates;
using DragDemo.ViewModels;

namespace DragDemo;

public class ViewLocator : IDataTemplate
{
    /// <summary>
    /// 将IControl修改成Control
    /// </summary>
    /// <param name="data"></param>
    /// <returns></returns>
    public Control Build(object data)
    {
        var name = data.GetType().FullName!.Replace("ViewModel", "View");
        var type = Type.GetType(name);

        if (type != null)
        {
            return (Control)Activator.CreateInstance(type)!;
        }

        return new TextBlock { Text = "Not Found: " + name };
    }

    public bool Match(object data)
    {
        return data is ViewModelBase;
    }
}

添加Avalonia.Themes.Fluent，因为预览版本的包已经独立需要单独安装

<PackageReference Include="Avalonia.Themes.Fluent" Version="11.0.0-preview5" />

打开App.axaml文件，修改为以下代码

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="using:DragDemo"
             RequestedThemeVariant="Light" 
             x:Class="DragDemo.App">
    <Application.DataTemplates>
        <local:ViewLocator/>
    </Application.DataTemplates>

    <Application.Styles>
        <FluentTheme DensityStyle="Compact"/>
    </Application.Styles>
    
</Application>

打开Views/MainWindow.axaml

在头部添加以下代码，让窗口无边框，设置指定窗口Height="38" Width="471"，参数让其不要占用整个屏幕，

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:DragDemo.ViewModels"
        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="DragDemo.Views.MainWindow"
        Icon="/Assets/avalonia-logo.ico"
        ExtendClientAreaToDecorationsHint="True"
        ExtendClientAreaChromeHints="NoChrome"
        ExtendClientAreaTitleBarHeightHint="-1"
        MaxHeight="38" MaxWidth="471"
        Title="DragDemo">
    <Window.Styles>
        <Style Selector="Window">
            <Setter Property="BorderThickness" Value="0"/>
            <Setter Property="Padding" Value="0"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="BorderBrush" Value="Transparent"/>
        </Style>
    </Window.Styles>
    <Design.DataContext>
        <vm:MainWindowViewModel/>
    </Design.DataContext>
    
    <StackPanel>
        <StackPanel Opacity="0.1" Height="38" Width="471">
        </StackPanel>
        <Border Name="Border" Width="471" CornerRadius="10" Opacity="1" Background="#FFFFFF">
            <Button>按钮</Button>    
        </Border>
    </StackPanel>
</Window>

以下代码在上面窗口用于设置窗口无边框

    <Window.Styles>
        <Style Selector="Window">
            <Setter Property="BorderThickness" Value="0"/>
            <Setter Property="Padding" Value="0"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="BorderBrush" Value="Transparent"/>
        </Style>
    </Window.Styles>

然后打开/Views/MainWindow.axaml.cs文件，将边框设置成无边框，并且设置窗体透明为WindowTransparencyLevel.Transparent

using Avalonia;
using Avalonia.Controls;

namespace DragDemo.Views;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.TransparencyLevelHint = WindowTransparencyLevel.Transparent;
        ExtendClientAreaToDecorationsHint = true;
        WindowState = WindowState.Maximized;
    }
}

效果图如下，因为限制了窗体最大大小，并且在按钮上面添加了透明区块，这样看起来就像是悬浮了

然后我们开始写指定组件拖动工具类，创建DragControlHelper.cs 以下就是封装的工具类 定义了一个ConcurrentDictionary静态参数，指定组件为Key ，Value为DragModule ，DragModule模型中定义了拖动的逻辑在调用StartDrag的时候传递需要拖动的组件，他会创建一个DragModule对象，创建的时候会创建定时器，当鼠标被按下时启动定时器，当鼠标被释放时定时器被停止，定时器用于平滑更新窗体移动，如果直接移动窗体会抖动。

using System;
using System.Collections.Concurrent;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Threading;
using Avalonia.VisualTree;

namespace DragDemo;


public class DragControlHelper
{
    private static ConcurrentDictionary<Control, DragModule> _dragModules = new();

    public static void StartDrag(Control userControl)
    {
        _dragModules.TryAdd(userControl, new DragModule(userControl));
    }

    public static void StopDrag(Control userControl)
    {
        if (_dragModules.TryRemove(userControl, out var dragModule))
        {
            dragModule.Dispose();
        }
    }
}

class DragModule : IDisposable
{
    /// <summary>
    /// 记录上一次鼠标位置
    /// </summary>
    private Point? lastMousePosition;

    /// <summary>
    /// 用于平滑更新坐标的计时器
    /// </summary>
    private DispatcherTimer _timer;

    /// <summary>
    /// 标记是否先启动了拖动
    /// </summary>
    private bool isDragging = false;

    /// <summary>
    /// 需要更新的坐标点
    /// </summary>
    private PixelPoint? _targetPosition;

    public Control UserControl { get; set; }

    public DragModule(Control userControl)
    {
        UserControl = userControl;
        // 添加当前控件的事件监听
        UserControl.PointerPressed += OnPointerPressed;
        UserControl.PointerMoved += OnPointerMoved;
        UserControl.PointerReleased += OnPointerReleased;

        // 初始化计时器
        _timer = new DispatcherTimer
        {
            Interval = TimeSpan.FromMilliseconds(10)
        };
        _timer.Tick += OnTimerTick;
    }


    /// <summary>
    /// 计时器事件
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void OnTimerTick(object sender, EventArgs e)
    {
        var window = UserControl.FindAncestorOfType<Window>();
        if (window != null && window.Position != _targetPosition)
        {
            // 更新坐标
            window.Position = (PixelPoint)_targetPosition;
        }
    }

    private void OnPointerPressed(object sender, PointerPressedEventArgs e)
    {
        if (!e.GetCurrentPoint(UserControl).Properties.IsLeftButtonPressed) return;
        // 启动拖动
        isDragging = true;
        // 记录当前坐标
        lastMousePosition = e.GetPosition(UserControl);
        e.Handled = true;
        // 启动计时器
        _timer.Start();
    }

    private void OnPointerReleased(object sender, PointerReleasedEventArgs e)
    {
        if (!isDragging) return;
        // 停止拖动
        isDragging = false;
        e.Handled = true;
        // 停止计时器
        _timer.Stop();
    }

    private void OnPointerMoved(object sender, PointerEventArgs e)
    {
        if (!e.GetCurrentPoint(UserControl).Properties.IsLeftButtonPressed) return;

        // 如果没有启动拖动，则不执行
        if (!isDragging) return;

        var currentMousePosition = e.GetPosition(UserControl);
        var offset =currentMousePosition - lastMousePosition.Value;
        var window = UserControl.FindAncestorOfType<Window>();
        if (window != null)
        {
            // 记录当前坐标
            _targetPosition = new PixelPoint(window.Position.X + (int)offset.X,
                window.Position.Y + (int)offset.Y);
        }
    }

    public void Dispose()
    {
        _timer.Stop();
        _targetPosition = null;
        lastMousePosition = null;
    }
}

打开MainWindow.axaml.cs，修改成以下代码 ，在渲染成功以后拿到Border(需要移动的组件)，添加到DragControlHelper.StartDrag(border);中，然后再OnUnloaded的时候将Border再卸载掉

using Avalonia;
using Avalonia.Controls;
using Avalonia.Media;
using Avalonia.Threading;

namespace DragDemo.Views;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.TransparencyLevelHint = WindowTransparencyLevel.Transparent;
        ExtendClientAreaToDecorationsHint = true;
        WindowState = WindowState.Maximized;
    }

    public override void Render(DrawingContext context)
    {
        base.Render(context);
        Dispatcher.UIThread.Post(() =>
        {
            var border = this.Find<Border>("Border");
            DragControlHelper.StartDrag(border);
        });
    }

    protected override void OnUnloaded()
    {
        var border = this.Find<Border>("Border");
        DragControlHelper.StopDrag(border);
        base.OnUnloaded();
    }
}

效果展示：