WPF 添加或删除Visual对象 画文字和画线

直接上码：

1.新建WpfApp解决方案

2.MainWindow.xaml文件代码如下：

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        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"
        xmlns:local="clr-namespace:WpfApp1" 
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="10*" ></RowDefinition>
        </Grid.RowDefinitions>

        <Button Name="button" Grid.Row="0" HorizontalAlignment="Center" Content="generate_bitmap" MinWidth="120"  MinHeight="30" Click="Button_Click"></Button>
        <local:DrawingCanvas x:Name="canvas" Grid.Row="1"></local:DrawingCanvas>
    </Grid>
</Window>

3.MainWindow.xaml.cs文件代码如下：

using System;
using System.Collections.Generic;
using System.Globalization;
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 WpfApp1
{
    public class DrawingCanvas : Canvas
    {
        private List<Visual> visuals = new List<Visual>();

        protected override Visual GetVisualChild(int index)
        {
            return visuals[index];
        }
        protected override int VisualChildrenCount
        {
            get
            {
                return visuals.Count;
            }
        }

        public void AddVisual(Visual visual)
        {
            visuals.Add(visual);

            base.AddVisualChild(visual);
            base.AddLogicalChild(visual);
        }

        public void DeleteVisual(Visual visual)
        {
            visuals.Remove(visual);

            base.RemoveVisualChild(visual);
            base.RemoveLogicalChild(visual);
        }

        public DrawingVisual GetVisual(Point point)
        {
            HitTestResult hitResult = VisualTreeHelper.HitTest(this, point);
            return hitResult.VisualHit as DrawingVisual;
        }

        private List<DrawingVisual> hits = new List<DrawingVisual>();
        public List<DrawingVisual> GetVisuals(Geometry region)
        {
            hits.Clear();
            GeometryHitTestParameters parameters = new GeometryHitTestParameters(region);
            HitTestResultCallback callback = new HitTestResultCallback(this.HitTestCallback);
            VisualTreeHelper.HitTest(this, null, callback, parameters);
            return hits;
        }

        private HitTestResultBehavior HitTestCallback(HitTestResult result)
        {
            GeometryHitTestResult geometryResult = (GeometryHitTestResult)result;
            DrawingVisual visual = result.VisualHit as DrawingVisual;
            if (visual != null &&
                geometryResult.IntersectionDetail == IntersectionDetail.FullyInside)
            {
                hits.Add(visual);
            }
            return HitTestResultBehavior.Continue;
        }
    }

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        public void Button_Click(object sender, RoutedEventArgs e)
        {        
            DrawingVisual visual = new DrawingVisual();
            using (DrawingContext dc = visual.RenderOpen())
            {
                // dc.PushOpacity(0.8);
                // dc.PushOpacityMask(Brushes.Red);

                dc.DrawRectangle(Brushes.Black, null, new Rect(0, 50, canvas.ActualWidth, canvas.ActualHeight));
                

                Pen pen = new Pen(Brushes.White, 1);
                pen.Freeze();

                //pixel align
                dc.PushGuidelineSet(new GuidelineSet(null,
                       new double[] { canvas.ActualHeight / 2 - pen.Thickness / 2, canvas.ActualHeight / 2 + pen.Thickness / 2 }));

                dc.DrawLine(pen, new Point(0, canvas.ActualHeight/2), new Point(canvas.ActualWidth, canvas.ActualHeight / 2));



                //display text               
                FormattedText gridTitle = new FormattedText("Hello World", CultureInfo.CurrentCulture,
                            FlowDirection.LeftToRight, new Typeface("Arial"), 13, Brushes.Red);
                dc.DrawText(gridTitle, new Point(50 + canvas.ActualWidth / 2, 50 + canvas.ActualHeight / 2));
            }
            canvas.AddVisual(visual);
        }
    }
}

3.效果如下：