如何在鼠标事件上绘制圆圈
如何在鼠标事件上绘制圆圈
提问于 2017-11-21 07:48:48
我是新来的WPF。
我想在画布上画一个圆圈在鼠标移动事件上。我已经写了逻辑把它拖到画布上。但是当鼠标点击我的画布时，我想要创建一个圆圈，它应该根据鼠标在画布上的移动来调整大小。
我怎样才能做到这一点？
这是我的密码
Ellipse elip = new Ellipse();
private double pointx;
private double pointy;
private void canvas_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
canvas.MouseMove -= MouseMove_NotDown;
canvas.MouseMove += canvas_PreviewMouseMove;
canvas.MouseUp += canvas_PreviewMouseUp;
Point location = e.MouseDevice.GetPosition(canvas);
elip = new Ellipse();
elip.Height = 1;
elip.Width = 1;
elip.Stroke = Brushes.Black;
elip.StrokeThickness = 2;
Canvas.SetTop(elip, location.Y + 1);
Canvas.SetLeft(elip, location.X + 1);
pointx = location.X + 1;
pointy = location.Y + 1;
canvas.Children.Add(elip);
}
private void MouseMove_NotDown(object sender, MouseEventArgs e)
{
canvas.Cursor = Cursors.Hand;
}
private void canvas_PreviewMouseMove(object sender, MouseEventArgs e)
{
try
{
Point location = e.MouseDevice.GetPosition(canvas);
double height = location.Y - pointy;
double width = location.X - pointx;
if (height >= 0 && width >= 0)
{
elip.Height = height;
elip.Width = width;
}
else if (height < 0 || width < 0)
{
if (height < 0)
{
elip.Height = height + (-height) + 1;
elip.Width = width;
}
else if (width < 0)
{
elip.Height = height;
elip.Width = width + (-width) + 1;
}
}
}
catch
{
}
}
private void canvas_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
elip.Stroke = Brushes.Black;
elip.StrokeThickness = 2;
canvas.MouseMove -= canvas_PreviewMouseMove;
canvas.MouseMove += MouseMove_NotDown;
canvas.MouseUp += canvas_PreviewMouseUp;
}回答 1
Stack Overflow用户
回答已采纳
发布于 2017-11-21 08:48:02
最好只附加你的听众一次。这使得您的应用程序逻辑更易于理解和调试。
如果WPF的canvas没有背景集，它将不会捕捉鼠标事件，除非在画布中有什么东西被点击，所以给它一个背景颜色(白色或透明是好的)
XAML：
<Window x:Class="mausing.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:mausing"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Canvas x:Name="canvas" Background="White"></Canvas>
</Grid>
C#：
public partial class MainWindow : Window
{
private Ellipse elip = new Ellipse();
private Point anchorPoint;
public MainWindow()
{
InitializeComponent();
canvas.MouseMove += canvas_MouseMove;
canvas.MouseUp += canvas_MouseUp;
canvas.MouseDown += canvas_MouseDown;
}
private void canvas_MouseDown(object sender, MouseButtonEventArgs e)
{
//capture the mouse on the canvas
//(this also helps us keep track of whether or not we're drawing)
canvas.CaptureMouse();
anchorPoint = e.MouseDevice.GetPosition(canvas);
elip = new Ellipse
{
Stroke = Brushes.Black,
StrokeThickness = 2
};
canvas.Children.Add(elip);
}
private void canvas_MouseMove(object sender, MouseEventArgs e)
{
//if we are not drawing, we don't need to do anything when the mouse moves
if (!canvas.IsMouseCaptured)
return;
Point location = e.MouseDevice.GetPosition(canvas);
double minX = Math.Min(location.X, anchorPoint.X);
double minY = Math.Min(location.Y, anchorPoint.Y);
double maxX = Math.Max(location.X, anchorPoint.X);
double maxY = Math.Max(location.Y, anchorPoint.Y);
Canvas.SetTop(elip, minY);
Canvas.SetLeft(elip, minX);
double height = maxY - minY;
double width = maxX - minX;
elip.Height = Math.Abs(height);
elip.Width = Math.Abs(width);
}
private void canvas_MouseUp(object sender, MouseButtonEventArgs e)
{
// we are now no longer drawing
canvas.ReleaseMouseCapture();
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/47407820
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