Avalonia开发实践（三）——实现GroupBox

原创已于 2024-12-02 13:18:37 修改 · 1.4k 阅读

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于 2024-07-24 11:25:52 首次发布

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一、开发背景

近期在项目中要用到GroupBox，结果发现Avalonia原生框架中竟然没有这一控件。想着这个控件也不算复杂，索性就自己实现一个好了。

二、坑的开始

熟悉桌面开发的朋友一定对下面这个经典的GroupBox样式不陌生——

这个样式看似简单，实则也不难实现。只要解决对标题处边框的擦除或遮盖这一个小问题就可以了。在WPF中，是用了OpacityMask来实现的。而在Avalonia中，仍然保留了这一属性，使得我们能很轻松地实现控件模板的移植。

但是事实真的这样吗？

当我把GroupBox的原生模板移植到Avalonia中，并且原模原样地实现了一个BorderGapMaskConverter之后，我发现该模板并不能正常工作。于是我单独写了个关于Border边框部分遮挡的用例，才发现DrawingBrush/VisualBrush并不能给OpacityMask使用，会发生如下报错：

Unable to cast object of type 'Avalonia.Media.DrawingBrush' to type 'Avalonia.Media.IImmutableBrush

后来在github上的源码仓库下也发现有人提了相同的issue，但似乎到今日仍未解决。。。

issue链接

三、开辟新思路

既然用遮罩的方式没办法实现，那不如就单纯画一个带有缺口的边框好了！

四、实现过程

1、先编写一个缺口矩形生成器，使用Geometry的图形生成指令

public static Geometry GetRoundedRectangleWithGap(Rect rect, double radiusX, double radiusY, double gapValue1, double gapValue2)
{
    StreamGeometry streamGeometry = new StreamGeometry();
    using (StreamGeometryContext streamGeometryContext = streamGeometry.Open())
    {
        var arcSize = new Size(radiusX, radiusY);
        var startPoint = new Point(Math.Max(gapValue1, gapValue2), rect.Top);
        var endPoint = new Point(Math.Min(gapValue1, gapValue2), rect.Top);
        streamGeometryContext.BeginFigure(startPoint, true);
        streamGeometryContext.LineTo(new Point(rect.Right - radiusX, rect.Top));
        streamGeometryContext.ArcTo(new Point(rect.Right, rect.Top + radiusY), arcSize, PiOver2, false, SweepDirection.Clockwise);
        streamGeometryContext.LineTo(new Point(rect.Right, rect.Bottom - radiusY));
        streamGeometryContext.ArcTo(new Point(rect.Right - radiusX, rect.Bottom), arcSize, PiOver2, false, SweepDirection.Clockwise);
        streamGeometryContext.LineTo(new Point(rect.Left + radiusX, rect.Bottom));
        streamGeometryContext.ArcTo(new Point(rect.Left, rect.Bottom - radiusY), arcSize, PiOver2, false, SweepDirection.Clockwise);
        streamGeometryContext.LineTo(new Point(rect.Left, rect.Top + radiusY));
        streamGeometryContext.ArcTo(new Point(rect.Left + radiusX, rect.Top), arcSize, PiOver2, false, SweepDirection.Clockwise);
        streamGeometryContext.LineTo(endPoint);
        streamGeometryContext.EndFigure(false);
    }
    return streamGeometry;
}

2、再定义一个专门用来绘制GroupBox边框的控件

internal class GroupBoxBorder : Control
{
    #region 私有变量
    private double _gapValue1;
    private double _gapValue2;
    #endregion

    public sealed override void Render(DrawingContext context)
    {
        var groupBox = this.TemplatedParent as GroupBox;
        if (groupBox == null)
            return;

        var pen = new Pen(groupBox.BorderBrush, groupBox.BorderThickness.Top);
        var streamGeometry = GeometryHelper.GetRoundedRectangleWithGap(new Rect(new Point(), Bounds.Size),
            groupBox.CornerRadius.TopLeft,
            groupBox.CornerRadius.TopLeft,
            _gapValue1,
            _gapValue2);
        context.DrawGeometry(null, pen, streamGeometry);
    }

    internal void UpdateBorder(double gapValue1, double gapValue2)
    {
        _gapValue1 = gapValue1;
        _gapValue2 = gapValue2;
        InvalidateVisual();
    }
}

3、GroupBox的模板及后台代码如下

<ControlTemplate>
	<Grid RowDefinitions="Auto,Auto,*">
		<Grid Grid.Row="1" Grid.RowSpan="2">
			<ContentPresenter x:Name="PART_ContentPresenter"
								RecognizesAccessKey="True"
								Padding="{TemplateBinding Padding}"
								Content="{TemplateBinding Content}"
								ContentTemplate="{TemplateBinding ContentTemplate}"
								Background="{TemplateBinding Background}"
								Foreground="{TemplateBinding Foreground}"
								HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
								VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
			<cy:GroupBoxBorder x:Name="PART_ContentBorder"/>
		</Grid>

		<Border x:Name="PART_HeaderBorder"
				Grid.Row="0"
				Grid.RowSpan="2"
				Padding="{TemplateBinding HeaderPadding}">
			<ContentPresenter x:Name="PART_HeaderPresenter"
								RecognizesAccessKey="True"
								Content="{TemplateBinding Header}"
								ContentTemplate="{TemplateBinding HeaderTemplate}"
								Margin="{TemplateBinding HeaderMargin}"
								HorizontalAlignment="{TemplateBinding HeaderHorizontalAlignment}"
								VerticalAlignment="{TemplateBinding HeaderVerticalAlignment}"/>
		</Border>
	</Grid>
</ControlTemplate>

/// <summary>
/// GroupBox
/// </summary>
[TemplatePart("PART_ContentBorder", typeof(GroupBoxBorder))]
[TemplatePart("PART_HeaderPresenter", typeof(ContentPresenter))]
[TemplatePart("PART_ContentPresenter", typeof(ContentPresenter))]
public class GroupBox : HeaderedContentControl
{
    #region 私有变量
    private GroupBoxBorder _contentBorder;
    private ContentPresenter _headerPresenter;
    private ContentPresenter _contentPresenter;
    #endregion

    #region 样式化属性
    /// <summary>
    /// Gets or sets the padding to place around the <see cref="HeaderedContentControl.Header"/> control.
    /// </summary>
    public Thickness HeaderPadding
    {
        get { return (Thickness)GetValue(HeaderPaddingProperty); }
        set { SetValue(HeaderPaddingProperty, value); }
    }

    /// <summary>
    /// Defines the <see cref="HeaderPadding"/> property.
    /// </summary>
    public static readonly StyledProperty<Thickness> HeaderPaddingProperty = AvaloniaProperty.Register<GroupBox, Thickness>("HeaderPadding", new Thickness(10, 0));

    /// <summary>
    /// Gets or sets the margin around the <see cref="HeaderedContentControl.Header"/> control.
    /// </summary>
    public Thickness HeaderMargin
    {
        get { return (Thickness)GetValue(HeaderMarginProperty); }
        set { SetValue(HeaderMarginProperty, value); }
    }

    /// <summary>
    /// Defines the <see cref="HeaderMargin"/> property.
    /// </summary>
    public static readonly StyledProperty<Thickness> HeaderMarginProperty = AvaloniaProperty.Register<GroupBox, Thickness>("HeaderMargin", new Thickness(5, 0));

    /// <summary>
    /// Gets or sets the horizontalAlignment of header.
    /// </summary>
    public HorizontalAlignment HeaderHorizontalAlignment
    {
        get { return (HorizontalAlignment)GetValue(HeaderHorizontalAlignmentProperty); }
        set { SetValue(HeaderHorizontalAlignmentProperty, value); }
    }

    /// <summary>
    /// Defines the <see cref="HeaderHorizontalAlignment"/> property.
    /// </summary>
    public static readonly StyledProperty<HorizontalAlignment> HeaderHorizontalAlignmentProperty = AvaloniaProperty.Register<GroupBox, HorizontalAlignment>("HeaderHorizontalAlignment", HorizontalAlignment.Left);

    /// <summary>
    /// Gets or sets the verticalAlignment of header.
    /// </summary>
    public VerticalAlignment HeaderVerticalAlignment
    {
        get { return (VerticalAlignment)GetValue(HeaderVerticalAlignmentProperty); }
        set { SetValue(HeaderVerticalAlignmentProperty, value); }
    }

    /// <summary>
    /// Defines the <see cref="HeaderVerticalAlignment"/> property.
    /// </summary>
    public static readonly StyledProperty<VerticalAlignment> HeaderVerticalAlignmentProperty = AvaloniaProperty.Register<GroupBox, VerticalAlignment>("HeaderVerticalAlignment", VerticalAlignment.Center);
    #endregion

    #region 重写方法
    /// <summary>
    /// OnApplyTemplate
    /// </summary>
    /// <param name="e"></param>
    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
    {
        base.OnApplyTemplate(e);
        _contentBorder = e.NameScope.Find<GroupBoxBorder>("PART_ContentBorder");
        _headerPresenter = e.NameScope.Get<ContentPresenter>("PART_HeaderPresenter");
        _contentPresenter = e.NameScope.Get<ContentPresenter>("PART_ContentPresenter");

        if (_contentBorder != null)
        {
            _headerPresenter.LayoutUpdated += (_s, _e) =>
            {
                _contentBorder.UpdateBorder(_headerPresenter.Bounds.Left - _headerPresenter.Margin.Left, _headerPresenter.Bounds.Right + _headerPresenter.Margin.Right);
            };
        }
    }
    #endregion
}

至此，一个基础的Avalonia框架下的GroupBox控件就开发完成了！

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