How do I only allow dragging in a circular path?
Is it possible to restrict the drag source to only move within the 开发者_运维技巧boundaries of a circular path when dragging it?
You don't need the 360-point path. Instead, as you are dragging, compute the current angle using Math.Atan2(Y,X)
, and then generate the point on the circle. You would still need to compute center
and radius
on resize and store them, or compute them inside MouseMove.
private void UserControl_MouseMove(object sender, MouseEventArgs e)
{
if (!isDraggingMarker)
return;
var position = e.GetPosition(this);
double angle = Math.Atan2(position.Y - center.Y, position.X - center.X);
var closest = new Point(center.X + radius*Math.Cos(angle),
center.Y + radius*Math.Sin(angle));
SetMarkerPosition(closest);
}
Create a circle of points and then when the mouse moves (and we are dragging) calculate the nearest point and snap to that point.
CircularDrag.xaml
<UserControl x:Class="DraggingBoundaries.CircularDrag"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
SizeChanged="UserControl_SizeChanged"
MouseMove="UserControl_MouseMove"
MouseLeave="UserControl_MouseLeave"
MouseLeftButtonUp="UserControl_MouseLeftButtonUp"
>
<Grid Background="White">
<Border
x:Name="Marker"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Width="14"
Height="14"
Background="CornflowerBlue"
CornerRadius="2"
BorderThickness="1"
BorderBrush="DarkGray"
MouseLeftButtonDown="Marker_MouseLeftButtonDown"
/>
</Grid>
</UserControl>
CircularDrag.xaml.cs
using System;
using System.Linq;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
namespace DraggingBoundaries
{
public partial class CircularDrag : UserControl
{
List<Point> allowedWheelMarkerPositions;
bool isDraggingMarker;
public CircularDrag()
{
InitializeComponent();
}
private void UserControl_SizeChanged(object sender, SizeChangedEventArgs e)
{
var center = new Point(e.NewSize.Width / 2, e.NewSize.Height / 2);
var radius = (center.X < center.Y ? center.X : center.Y) - 15;
allowedWheelMarkerPositions = CreateCirclePath(center, radius);
SetMarkerPosition(allowedWheelMarkerPositions.First());
}
private List<Point> CreateCirclePath(Point center, double radius)
{
var result = new List<Point>();
for (double angle = 0; angle <= 360; angle++)
{
double angleR = angle * (Math.PI / 180);
double x = center.X + Math.Cos(angleR) * radius;
double y = center.Y - Math.Sin(angleR) * radius;
result.Add(new Point(x, y));
}
return result;
}
private void UserControl_MouseMove(object sender, MouseEventArgs e)
{
if (!isDraggingMarker)
return;
var position = e.GetPosition(this);
var closest = allowedWheelMarkerPositions
.OrderBy(p => GetDistance(position, p))
.First();
SetMarkerPosition(closest);
}
private void SetMarkerPosition(Point closest)
{
Marker.Margin = new Thickness(closest.X - Marker.Width / 2, closest.Y - Marker.Height / 2, 0, 0);
}
private double GetDistance(Point a, Point b)
{
var deltaX = a.X - b.X;
var deltaY = a.Y - b.Y;
return Math.Sqrt(Math.Pow(deltaX, 2) + Math.Pow(deltaY, 2));
}
private void Marker_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
isDraggingMarker = true;
}
private void UserControl_MouseLeave(object sender, MouseEventArgs e)
{
isDraggingMarker = false;
}
private void UserControl_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
isDraggingMarker = false;
}
}
}
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