使用WPF创建画图箭头

今天要给leader line画个箭头，所以就google一下，找到下面的文章，写的不错，可以实现我的需求，所以就摘录下来。

我把源代码中的arraw.cs加入到我的工程，修改了namespace，然后写了个方法进行调用：

private void DrawLeaderLineArrow(Point startPt, Point endPt)
{
Arrowarrow = new Arrow();
arrow.X1 = startPt.X;
arrow.Y1 = startPt.Y;
arrow.X2 = endPt.X;
arrow.Y2 = endPt.Y;
arrow.HeadWidth = 15;
arrow.HeadHeight = 5;
arrow.Stroke= Brushes.Black;
arrow.StrokeThickness = 1;
_canvas.Children.Add(arrow);
}

WPF Arrowand Custom Shapes

Download source files - 41 KB

Introduction

WPF is the best UI Framework ever. It provides us with a large arsenal of vector graphic types such as

Line

,

Ellipse

,

Path

and others. Sometimes we need shapes which are not provided in the WPF arsenal (such an

Arrow

), and with all due respect to the

Path

shape, which can be used to create any type of 2D shape, we do not want to recalculate each point every time. This is a good reason and opportunity to create a custom shape.

Background

WPF provides two kinds of vector types: Shapes and Geometries.

Shape

is any type that derives from the

Shape

base class. It provides

Fill

,

Stroke

and other properties for coloring, and is actually a

FrameworkElement

. Thus we can place shapes inside

Panel

s, we can register shapes routed events and do anything related to

FrameworkElement

. (MSDN)

Geometry

is any type that derives from the

Geometry

base type. It provides properties for describing any type of 2D geometry. A geometry is actually a

Freezable

type, thus can be frozen. A frozen object provides better performance by not notifying changes, and can be safely accessed by other threads.

Geometry

is not

Visual

, hence should be painted by other types such as

Path

. (MSDN)

Using the Code

Now that we have a little background, and we know what the differences between a

Geometry

and

Shape

are, we can create our shape based on one of these two types. Correct?

Well, surprisingly we can't base our custom shape on the

Geometry

type, since its one and only default constructor is marked as internal. Shame on you Microsoft.

Don't worry! We still have an option to base our custom shape on the

Shape

base class.

Now, let’s say that we want to create an

Arrow

shape. An arrow is actually a kind of line, so let’s derive our custom type from the WPF

Line

type which has

X1

,

Y1

,

X2

and

Y2

properties.

Ooopps...

Line

is sealed! (Shame on you twice).

Never mind, let's derive directly from the

Shape

base class, and add

X1

,

Y1

,

X2

,

Y2

and two additional properties for defining the arrow's head

width

and

height

.

Our code should end up with something like this:


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    public sealed class Arrow: Shape
{
public static readonly DependencyProperty X1Property = ...;
public static readonly DependencyProperty Y1Property = ...;
public static readonly DependencyProperty HeadHeightProperty = ...;
...

[TypeConverter(typeof(LengthConverter))]
public double X1
{
get { return (double)base.GetValue(X1Property); }
set { base.SetValue(X1Property, value); }
}

[TypeConverter(typeof(LengthConverter))]
public double Y1
{
get { return (double)base.GetValue(Y1Property); }
set { base.SetValue(Y1Property, value); }
}

[TypeConverter(typeof(LengthConverter))]
public double HeadHeight
{
get { return (double)base.GetValue(HeadHeightProperty); }
set { base.SetValue(HeadHeightProperty, value); }
}
...

protected override GeometryDefiningGeometry
{
get
{
// Create a StreamGeometryfor describing the shape
StreamGeometrygeometry = new StreamGeometry();
geometry.FillRule = FillRule.EvenOdd;

using (StreamGeometryContext context = geometry.Open())
{
InternalDrawArrowGeometry(context);
}

// Freeze the geometry for performance benefits
geometry.Freeze();

return geometry;
}
}

/// <summary>
/// Draws an Arrow
/// </summary>
private void InternalDrawArrowGeometry(StreamGeometryContext context)
{
double theta = Math.Atan2(Y1 - Y2, X1 - X2);
double sint = Math.Sin(theta);
double cost = Math.Cos(theta);

Point pt1 = new Point(X1, this.Y1);
Point pt2 = new Point(X2, this.Y2);

Point pt3 = new Point(
X2 + (HeadWidth * cost - HeadHeight * sint),
Y2 + (HeadWidth * sint + HeadHeight * cost));

Point pt4 = new Point(
X2 + (HeadWidth * cost + HeadHeight * sint),
Y2 - (HeadHeight * cost - HeadWidth * sint));

context.BeginFigure(pt1, true, false);
context.LineTo(pt2, true, true);
context.LineTo(pt3, true, true);
context.LineTo(pt2, true, true);
context.LineTo(pt4, true, true);
}
}

As you can see, it is very easy to implement a custom shape, thanks to the great work in the

Shape

base class. All we have to do is derive our custom shape type from

Shape

, and override the

DefiningGeometry

property. This property should return a

Geometry

of any type.