一个Pan&Zoom的Behavior

Pan&Zoom是个很常用的操作，但是不想每次都去重新写各种GerstureListener事件，所以就参考这篇文章，改写了个简单的Behavior。

public class ZoomAndPanBehavior2 : Behavior<Image>
{
private Image _currentImage { get { return AssociatedObject as Image; } }
 
private PhoneApplicationPage _currentPage
{
get
{
var rootFrame = Application.Current.RootVisual as PhoneApplicationFrame;
var currentPage = rootFrame.Content as PhoneApplicationPage;
return currentPage;
}
}
 
private GestureListener _gl { get { return GestureService.GetGestureListener(_currentImage); } }
 
private double _totalImageScale = 1d;
private Point _imagePosition = new Point(0, 0);
 
private Point _oldFinger1;
private Point _oldFinger2;
private double _oldScaleFactor; //旧的缩放因子
 
private CompositeTransform _compositeTransfrom;
private MatrixTransform _previousTransform;
private TransformGroup _transfromGruop;
private TransformGroup _currentGroup;
 
bool isDragging;
bool isPinching;
Point ptPinchPositionStart;
 
protected override void OnAttached()
{
base.OnAttached();
_compositeTransfrom = new CompositeTransform();
_previousTransform = new MatrixTransform { Matrix = Matrix.Identity };
_transfromGruop = new TransformGroup();
_currentGroup = new TransformGroup();
_currentGroup.Children.Add(_compositeTransfrom);
_transfromGruop.Children.Add(_currentGroup);
_transfromGruop.Children.Add(_previousTransform);
_currentImage.RenderTransform = _transfromGruop;
_currentImage.RenderTransformOrigin = new Point(0, 0);
_gl.DragStarted += _gl_DragStarted;
_gl.DragDelta += _gl_DragDelta;
_gl.PinchStarted += _gl_PinchStarted;
_gl.PinchDelta += _gl_PinchDelta;
_gl.PinchCompleted += _gl_PinchCompleted;
_gl.Hold += _gl_Hold;
_gl.DoubleTap += _gl_DoubleTap;
}
 
protected override void OnDetaching()
{
base.OnDetaching();
_gl.DragStarted -= _gl_DragStarted;
_gl.DragDelta -= _gl_DragDelta;
_gl.PinchStarted -= _gl_PinchStarted;
_gl.PinchDelta -= _gl_PinchDelta;
_gl.PinchCompleted -= _gl_PinchCompleted;
_gl.Hold -= _gl_Hold;
_gl.DoubleTap -= _gl_DoubleTap;
_compositeTransfrom = null;
}
 
void _gl_DoubleTap(object sender, Microsoft.Phone.Controls.GestureEventArgs e)
{
Point imageCenter = e.GetPosition(_currentImage);
if (_compositeTransfrom.ScaleX != 2)
_compositeTransfrom.ScaleY = _compositeTransfrom.ScaleX = 2;
else
_compositeTransfrom.ScaleX = _compositeTransfrom.ScaleY = 1;
_compositeTransfrom.CenterX = imageCenter.X;
_compositeTransfrom.CenterY = imageCenter.Y;
}
 
void _gl_Hold(object sender, Microsoft.Phone.Controls.GestureEventArgs e)
{
 
}
 
void _gl_PinchStarted(object sender, PinchStartedGestureEventArgs e)
{
_oldFinger1 = e.GetPosition(_currentImage, 0);
_oldFinger2 = e.GetPosition(_currentImage, 1);
_oldScaleFactor = 1;
isPinching = true;
}
void _gl_PinchDelta(object sender, PinchGestureEventArgs e)
{
//DistanceRatio表示缩放之后手指之间的距离与缩放前手指之间距离的比例
var scaleFactor = e.DistanceRatio / _oldScaleFactor;
 
var currentFinger1 = e.GetPosition(_currentImage, 0);
var currentFinger2 = e.GetPosition(_currentImage, 1);
 
Point tranlationDelta;
tranlationDelta = GetTranslationDelta(currentFinger1, currentFinger2, _oldFinger1, _oldFinger2, _imagePosition, scaleFactor);
 
_oldFinger1 = currentFinger1;
_oldFinger2 = currentFinger2;
_oldScaleFactor = e.DistanceRatio;
UpdateImage(scaleFactor, tranlationDelta);
}
 
void _gl_PinchCompleted(object sender, PinchGestureEventArgs e)
{
isPinching = false;
}
 
void _gl_DragStarted(object sender, DragStartedGestureEventArgs e)
{
 
}
 
void _gl_DragDelta(object sender, DragDeltaGestureEventArgs e)
{
if (isPinching)
return;
if (_totalImageScale > 1 || _compositeTransfrom.ScaleX > 1)
{
_compositeTransfrom.TranslateX += e.HorizontalChange;
_compositeTransfrom.TranslateY += e.VerticalChange;
}
}
 
private void UpdateImage(double scaleFactor, Point delta)
{
_totalImageScale *= scaleFactor;
_imagePosition = new Point(_imagePosition.X + delta.X, _imagePosition.Y + delta.Y);
 
if (_totalImageScale > 1)
{
_compositeTransfrom.ScaleX = _totalImageScale;
_compositeTransfrom.ScaleY = _totalImageScale;
_compositeTransfrom.TranslateX = _imagePosition.X;
_compositeTransfrom.TranslateY = _imagePosition.Y;
}
else
{
_compositeTransfrom.ScaleX = _compositeTransfrom.ScaleY = 1;
_compositeTransfrom.TranslateX = _compositeTransfrom.TranslateY = 0;
_imagePosition = new Point(0, 0);
}
}
 
private Point GetTranslationDelta(Point currentFinger1, Point currentFinger2, Point oldFinger1,
Point oldFinger2, Point currentPosition, double scaleFactor)
{
var newPos1 = new Point(
currentFinger1.X + (currentPosition.X - oldFinger1.X) * scaleFactor,
currentFinger1.Y + (currentPosition.Y - oldFinger1.Y) * scaleFactor);
 
var newPos2 = new Point(
currentFinger2.X + (currentPosition.X - oldFinger2.X) * scaleFactor,
currentFinger2.Y + (currentPosition.Y - oldFinger2.Y) * scaleFactor);
 
var newPos = new Point(
(newPos1.X + newPos2.X) / 2,
(newPos1.Y + newPos2.Y) / 2);
 
return new Point(
newPos.X - currentPosition.X,
newPos.Y - currentPosition.Y);
}
}