我希望我的Canvas可以自动调整大小以适应其项目的大小，这样ScrollViewer滚动条就会有正确的范围。 这是否可以在XAML中完成？
<ScrollViewer HorizontalScrollBarVisibility="Auto" x:Name="_scrollViewer">
<Grid x:Name ="_canvasGrid" Background="Yellow">
<Canvas x:Name="_canvas" HorizontalAlignment="Left" VerticalAlignment="Top" Background="Green"></Canvas>
<Line IsHitTestVisible="False" .../>
</Grid>
</ScrollViewer>
这是不可能的（请参见下面MSDN的片段）。但是，如果您想要滚动条和自动调整大小，请考虑使用 Grid（网格） ，并使用Margin属性在此Grid上定位您的项目。Grid会告诉ScrollViewer他想要多大，您将获得滚动条。Canvas始终告诉ScrollViewer它不需要任何大小。：）
Grid让您同时享受两个世界 - 只要将所有元素放入单个单元格中，您就可以同时获得：任意定位和自动调整大小。总的来说，最好记住大多数面板控件（DockPanel、StackPanel等）都可以通过Grid控件实现。
来自MSDN：
Canvas是唯一一个没有固有布局特性的面板元素。除非它是自动调整其子元素大小的元素的子级，否则Canvas具有默认高度和宽度属性为零。Canvas的子元素永远不会被重新调整大小，它们只是被定位在它们指定的坐标上。这为不需要或不希望固有大小约束或对齐的情况提供了灵活性。对于希望自动调整大小并对齐子内容的情况，通常最好使用Grid元素。
希望这能帮到您。
我这里只是在复制 illef 的回答，但是针对 PilotBob 的问题，你只需要像这样定义一个画布对象：
public class CanvasAutoSize : Canvas
{
protected override System.Windows.Size MeasureOverride(System.Windows.Size constraint)
{
base.MeasureOverride(constraint);
double width = base
.InternalChildren
.OfType<UIElement>()
.Max(i => i.DesiredSize.Width + (double)i.GetValue(Canvas.LeftProperty));
double height = base
.InternalChildren
.OfType<UIElement>()
.Max(i => i.DesiredSize.Height + (double)i.GetValue(Canvas.TopProperty));
return new Size(width, height);
}
}
然后在你的XAML中使用CanvasAutoSize。
<local:CanvasAutoSize VerticalAlignment="Top" HorizontalAlignment="Left"></local:CanvasAutoSize>
相比于上面使用网格作为解决方案，我更喜欢这个方案，因为它通过附加属性的方式工作，只需要在元素上设置较少的属性。
if (!base.InternalChildren.OfType<UIElement>().Any()) return new System.Windows.Size(1, 1);，虽然可能有更优雅的处理方法。 - Tony Delroy我认为你可以通过重写MeasureOverride或ArrangeOverride方法来调整Canvas的大小。
这项工作并不难。
你可以查看这篇文章：http://illef.tistory.com/entry/Canvas-supports-ScrollViewer
希望这能帮到你。
谢谢。
重写ArrangeOverride和MeasureOverride并不那么复杂。你还必须编写至少同样数量的代码来处理Grid/Margin的愚蠢。所以就是这样。
以下是一个更完整的解决方案。非零边距行为未经测试。如果你需要除了Left和Top之外的任何东西，那么这至少提供了一个起点。
警告：你必须使用AutoResizeCanvas.Left和AutoResizeCanvas.Top附加属性，而不是Canvas.Left和Canvas.Top。剩余的Canvas属性尚未实现。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace Mu.Controls
{
public class AutoResizeCanvas : Panel
{
public static double GetLeft(DependencyObject obj)
{
return (double)obj.GetValue(LeftProperty);
}
public static void SetLeft(DependencyObject obj, double value)
{
obj.SetValue(LeftProperty, value);
}
public static readonly DependencyProperty LeftProperty =
DependencyProperty.RegisterAttached("Left", typeof(double),
typeof(AutoResizeCanvas),
new FrameworkPropertyMetadata(0.0, OnLayoutParameterChanged));
private static void OnLayoutParameterChanged(
DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// invalidate the measure of the enclosing AutoResizeCanvas.
while (d != null)
{
AutoResizeCanvas canvas = d as AutoResizeCanvas;
if (canvas != null)
{
canvas.InvalidateMeasure();
return;
}
d = VisualTreeHelper.GetParent(d);
}
}
public static double GetTop(DependencyObject obj)
{
return (double)obj.GetValue(TopProperty);
}
public static void SetTop(DependencyObject obj, double value)
{
obj.SetValue(TopProperty, value);
}
public static readonly DependencyProperty TopProperty =
DependencyProperty.RegisterAttached("Top",
typeof(double), typeof(AutoResizeCanvas),
new FrameworkPropertyMetadata(0.0, OnLayoutParameterChanged));
protected override Size MeasureOverride(Size constraint)
{
Size availableSize = new Size(double.MaxValue, double.MaxValue);
double requestedWidth = MinimumWidth;
double requestedHeight = MinimumHeight;
foreach (var child in base.InternalChildren)
{
FrameworkElement el = child as FrameworkElement;
if (el != null)
{
el.Measure(availableSize);
Rect bounds, margin;
GetRequestedBounds(el,out bounds, out margin);
requestedWidth = Math.Max(requestedWidth, margin.Right);
requestedHeight = Math.Max(requestedHeight, margin.Bottom);
}
}
return new Size(requestedWidth, requestedHeight);
}
private void GetRequestedBounds(
FrameworkElement el,
out Rect bounds, out Rect marginBounds
)
{
double left = 0, top = 0;
Thickness margin = new Thickness();
DependencyObject content = el;
if (el is ContentPresenter)
{
content = VisualTreeHelper.GetChild(el, 0);
}
if (content != null)
{
left = AutoResizeCanvas.GetLeft(content);
top = AutoResizeCanvas.GetTop(content);
if (content is FrameworkElement)
{
margin = ((FrameworkElement)content).Margin;
}
}
if (double.IsNaN(left)) left = 0;
if (double.IsNaN(top)) top = 0;
Size size = el.DesiredSize;
bounds = new Rect(left + margin.Left, top + margin.Top, size.Width, size.Height);
marginBounds = new Rect(left, top, size.Width + margin.Left + margin.Right, size.Height + margin.Top + margin.Bottom);
}
protected override Size ArrangeOverride(Size arrangeSize)
{
Size availableSize = new Size(double.MaxValue, double.MaxValue);
double requestedWidth = MinimumWidth;
double requestedHeight = MinimumHeight;
foreach (var child in base.InternalChildren)
{
FrameworkElement el = child as FrameworkElement;
if (el != null)
{
Rect bounds, marginBounds;
GetRequestedBounds(el, out bounds, out marginBounds);
requestedWidth = Math.Max(marginBounds.Right, requestedWidth);
requestedHeight = Math.Max(marginBounds.Bottom, requestedHeight);
el.Arrange(bounds);
}
}
return new Size(requestedWidth, requestedHeight);
}
public double MinimumWidth
{
get { return (double)GetValue(MinimumWidthProperty); }
set { SetValue(MinimumWidthProperty, value); }
}
public static readonly DependencyProperty MinimumWidthProperty =
DependencyProperty.Register("MinimumWidth", typeof(double), typeof(AutoResizeCanvas),
new FrameworkPropertyMetadata(300.0,FrameworkPropertyMetadataOptions.AffectsMeasure));
public double MinimumHeight
{
get { return (double)GetValue(MinimumHeightProperty); }
set { SetValue(MinimumHeightProperty, value); }
}
public static readonly DependencyProperty MinimumHeightProperty =
DependencyProperty.Register("MinimumHeight", typeof(double), typeof(AutoResizeCanvas),
new FrameworkPropertyMetadata(200.0,FrameworkPropertyMetadataOptions.AffectsMeasure));
}
}
我看到你有一个可行的解决方案，但是我想分享一下我的想法。
<Canvas x:Name="topCanvas">
<Grid x:Name="topGrid" Width="{Binding ElementName=topCanvas, Path=ActualWidth}" Height="{Binding ElementName=topCanvas, Path=ActualHeight}">
...Content...
</Grid>
</Canvas>
以上技术将允许您在画布内嵌套网格并进行动态调整大小。通过使用维度绑定，可以将动态材料与静态材料混合使用，进行分层等操作。有太多可能性可以提到，有些比其他的更难。例如，我使用这种方法模拟内容从一个网格位置移动到另一个网格位置的动画效果-在动画完成事件中进行实际放置。祝你好运。
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
autoSizeCanvas(canvas1);
}
void autoSizeCanvas(Canvas canv)
{
int height = canv.Height;
int width = canv.Width;
foreach (UIElement ctrl in canv.Children)
{
bool nullTop = ctrl.GetValue(Canvas.TopProperty) == null || Double.IsNaN(Convert.ToDouble(ctrl.GetValue(Canvas.TopProperty))),
nullLeft = ctrl.GetValue(Canvas.LeftProperty) == null || Double.IsNaN(Convert.ToDouble(ctrl.GetValue(Canvas.LeftProperty)));
int curControlMaxY = (nullTop ? 0 : Convert.ToInt32(ctrl.GetValue(Canvas.TopProperty))) +
Convert.ToInt32(ctrl.GetValue(Canvas.ActualHeightProperty)
),
curControlMaxX = (nullLeft ? 0 : Convert.ToInt32(ctrl.GetValue(Canvas.LeftProperty))) +
Convert.ToInt32(ctrl.GetValue(Canvas.ActualWidthProperty)
);
height = height < curControlMaxY ? curControlMaxY : height;
width = width < curControlMaxX ? curControlMaxX : width;
}
canv.Height = height;
canv.Width = width;
}
将控件的高度/宽度绑定到画布中实际大小对我很有帮助：
<ScrollViewer VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Visible">
<Canvas Height="{Binding ElementName=myListBox, Path=ActualHeight}"
Width="{Binding ElementName=myListBox, Path=ActualWidth}">
<ListBox x:Name="myListBox" />
</Canvas>
</ScrollViewer>
public class AutoResizedCanvas : Canvas
{
protected override System.Windows.Size MeasureOverride(System.Windows.Size constraint)
{
base.MeasureOverride(constraint);
double width = base
.InternalChildren
.OfType<UIElement>()
.Where(i => i.GetValue(Canvas.LeftProperty) != null)
.Max(i => i.DesiredSize.Width + (double)i.GetValue(Canvas.LeftProperty));
if (Double.IsNaN(width))
{
width = 0;
}
double height = base
.InternalChildren
.OfType<UIElement>()
.Where(i => i.GetValue(Canvas.TopProperty) != null)
.Max(i => i.DesiredSize.Height + (double)i.GetValue(Canvas.TopProperty));
if (Double.IsNaN(height))
{
height = 0;
}
return new Size(width, height);
}
}
使用 Grid 可以自动调整大小以适应内容，而无需设置其他参数，只需要设置 VerticalAlignment 和 HorizontalAlignment。例如：
<Grid VerticalAlignment="Top" HorizontalAlignment="Center">
<Polygon Points="0, 0, 0, 100, 80, 100" Panel.ZIndex="6" Fill="Black" Stroke="Black" StrokeStartLineCap="Round" StrokeDashCap="Round" StrokeLineJoin="Round" StrokeThickness="10"/>
</Grid>
我也遇到了这个问题，我的问题是当Canvas调整大小时，网格没有自动调整大小，这要归功于重写的MeasureOverride函数。
我的问题： WPF MeasureOverride loop