C# WPF中如何获得在Canvas中控件的高度和宽度

Question

一个Border在Canvas中，因为要自动缩放，高度和宽度都是设成自动的。如果用ActualHeight和ActualWidth的话，返回的值都是零。要实现的效果是一根线的起点随着Border高度的变化而始终附着在右边的中点上。

Answer 1

[code=XAML]
<Grid>
   <Canvas x:Name="cvs" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Background="Green">
      <Border BorderThickness="2" BorderBrush="Red" Margin="0" Width="{Binding ElementName=cvs, Path=ActualWidth}" Height="{Binding ElementName=cvs, Path=ActualHeight}"/>
   </Canvas>
</Grid>
[/code]

Answer 2

上边的代码不对，不是你要的效果。到底是Canvas在Border里还是Border在Canvas里？
按照Border在Canvas里算
[code=XAML]
<Canvas x:Name="cvs"  VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Margin="200,300,150,10" Background="Green">
    <Border x:Name="bdr" Height="2" BorderBrush="Red" BorderThickness="1"/>
</Canvas>
[/code]
cvs.SizeChanged += delegate
{
    //Console.WriteLine(cvs.ActualHeight);
    //Console.WriteLine(cvs.ActualWidth);
    bdr.Margin = new Thickness(5, cvs.ActualHeight / 2 - 2, 0, 0);
    bdr.Width = cvs.ActualWidth - 5;
};
按照Canvas在Border里面算
[code=XAML]
<Border x:Name="bdr" Margin="200,300,150,10" Background="Green">
    <Canvas x:Name="cvs" Height="2" Background="Red"/>
</Border>
[/code]bdr.SizeChanged += delegate
{
    //Console.WriteLine(bdr.ActualHeight);
    //Console.WriteLine(bdr.ActualWidth);
    cvs.Margin = new Thickness(5, bdr.ActualHeight / 2 - 2, 0, bdr.ActualHeight / 2 - 2);
    Console.WriteLine(cvs.Margin);
    cvs.Width = bdr.ActualWidth - 5;
};

Answer 3

Foxer: 谢谢回复！我之前讲得不够清楚，应该是Border在Canvas里面。但在我的程序中Border是由代码动态生成，数量是不定的。象数据库中的两个有关联的表一样，有联系的两个border中间由线段连接，从一个border右边的中点连到
另一个border左边的中点。移动一个border时，线段也会跟着移动。下面的代码实现了Border的移动[code=XAML]<Window x:Class="BorderTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1"
    MouseMove="Window_MouseMove"
    MouseUp="Window_MouseUp">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition  Height="20"/>
            <RowDefinition />
        </Grid.RowDefinitions>
        <Button Name="btnGo" Click="btnGo_Click" Grid.Row="0">Go</Button>
        <Canvas x:Name="myCanvas" Grid.Row="1"  VerticalAlignment="Stretch" HorizontalAlignment="Stretch"  Background="Green">
        </Canvas>
    </Grid>
</Window>[/code]using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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 BorderTest
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        bool IsMouseDown = false;
        Point mousePoint;
        object mouseCtrl = null;        public Window1()
        {
            InitializeComponent();
        }        private void myBorder_MouseDown(object sender, MouseButtonEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                IsMouseDown = true;
                mousePoint = e.GetPosition(this.myCanvas);
                mouseCtrl = sender;
            }
        }        private void Window_MouseMove(object sender, MouseEventArgs e)
        {
            if (IsMouseDown)
            {
                if (e.LeftButton == MouseButtonState.Pressed)
                {
                    Point theMousePoint = e.GetPosition(this.myCanvas);
                    Point theMousePointToBorder = e.GetPosition((UIElement)mouseCtrl);
                    double canvasHeight = myCanvas.ActualHeight;
                    double canvasWidth = myCanvas.ActualWidth;
                    double borderHeight = ((Border)mouseCtrl).ActualHeight;
                    double borderWidth = ((Border)mouseCtrl).ActualWidth;
                    double theLeft = theMousePoint.X - (mousePoint.X - Canvas.GetLeft(((UIElement)mouseCtrl)));
                    double theTop = theMousePoint.Y - (mousePoint.Y - Canvas.GetTop(((UIElement)mouseCtrl)));                    //Restrict border object of being dragged within canvas
                    if (theLeft < 0.0)
                        theLeft = 0.0;
                    if (theLeft > (canvasWidth - borderWidth))
                        theLeft = canvasWidth - borderWidth;
                    if (theTop < 0.0)
                        theTop = 0.0;
                    if (theTop > (canvasHeight - borderHeight))
                        theTop = canvasHeight - borderHeight;                    Canvas.SetLeft((UIElement)mouseCtrl, theLeft);
                    Canvas.SetTop((UIElement)mouseCtrl, theTop);                    mousePoint = theMousePoint;
                }
            }
        }        private void Window_MouseUp(object sender, MouseButtonEventArgs e)
        {
            if (IsMouseDown)
            {
                IsMouseDown = false;
            }
        }        private void btnGo_Click(object sender, RoutedEventArgs e)
        {
            Border myBorder = new Border();
            myBorder.Background = Brushes.LightBlue;
            myBorder.BorderBrush = Brushes.Black;
            myBorder.BorderThickness = new Thickness(2);
            myBorder.CornerRadius = new CornerRadius(10);
            myBorder.Padding = new Thickness(10.0);
            myBorder.AllowDrop = true;
            myBorder.MouseDown += new MouseButtonEventHandler(myBorder_MouseDown);            TextBlock myText = new TextBlock();
            myText.Text = "Test Message";            myBorder.Child = myText;            Canvas.SetLeft(myBorder, 100);
            Canvas.SetTop(myBorder, 20);            // Add a Line Element
            Line myLine = new Line();
            myLine.Stroke = System.Windows.Media.Brushes.Red;
            myLine.X1 = 1;
            myLine.X2 = 100;
            myLine.Y1 = 1;
            myLine.Y2 = 100;
            myLine.HorizontalAlignment = HorizontalAlignment.Left;
            myLine.VerticalAlignment = VerticalAlignment.Center;
            myLine.StrokeThickness = 2;            Canvas.SetLeft(myLine, 150);
            Canvas.SetTop(myLine, 30);            myCanvas.Children.Add(myBorder);
            myCanvas.Children.Add(myLine);
        }
    }
}

Answer 4

看别人的代码还是费劲啊..我觉得你的程序在原理上好像没有问题，可能出现的问题是ActualHeight这种属性只有在显示出来以后才有值。
你先研究吧，今天比较忙，抱歉

Answer 5

搞定了。要看IsLoaded属性是否为true.