namespace AvalonApplication7
{

    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        //Initialize the application by calling a method
        //to apply adorners to all children of the respective
        //Canvas.
        private void StartUp(object sender, EventArgs args)
        {
            ApplyAdornersToCanvasChildren(mainCanvas);
        }

        //Iterates through the Canvas' children finding all of
        //the FrameworkElements; it then applies a CustomResizeAdorner
        //to each one.

        void ApplyAdornersToCanvasChildren(Canvas canvas)
        {
            AdornerLayer al = AdornerDecorator.GetAdornerLayer(canvas);

            foreach (FrameworkElement fxe in canvas.Children)
                if (al.GetAdorners(fxe) == null)
                    al.Add(new CustomResizeAdorner(fxe));
        }

    }

   
    public class CustomResizeAdorner : Adorner
    {
        //The visual elements used as the Adorners.  The Thumb
        //element is used because it takes care of handling the
        //lower level mouse input.
        Thumb topLeft, topRight, bottomLeft, bottomRight;

        //Initialize the CustomResizeAdorner.
        public CustomResizeAdorner(UIElement adornedElement) : base(adornedElement)
        {
            //Call a helper method to instantiate the Thumbs
            //with a given Cursor.
            BuildAdornerCorner(ref topLeft, Cursors.SizeNWSE);
            BuildAdornerCorner(ref topRight, Cursors.SizeNESW);
            BuildAdornerCorner(ref bottomLeft, Cursors.SizeNESW);
            BuildAdornerCorner(ref bottomRight, Cursors.SizeNWSE);

            //Add handlers for resizing on the bottom left and right.
            //Leaving the handling of the other two corners as an exercise
            //to the reader.
            bottomLeft.DragDelta += new DragDeltaEventHandler(HandleBottomLeft);
            bottomRight.DragDelta += new DragDeltaEventHandler(HandleBottomRight);
        }

        //Handle resize for the bottom right adorner widget.
        void HandleBottomRight(object sender, DragDeltaEventArgs args)
        {
            FrameworkElement fxe = AdornedElement as FrameworkElement;
            Thumb hitThumb = sender as Thumb;
            if (fxe == null || hitThumb == null)
                return;

            EnforceSize(fxe);

            //Change the size by the amount the user drags the mouse as
            //long as it's larger than the width or height of an adorner, respectively.
            fxe.Width = Math.Max(args.HorizontalChange + fxe.Width, hitThumb.DesiredSize.Width);
            fxe.Height = Math.Max(args.VerticalChange + fxe.Height, hitThumb.DesiredSize.Height);
        }

        //Handle resize for the bottom left adorner widget.
        void HandleBottomLeft(object sender, DragDeltaEventArgs args)
        {
            FrameworkElement fxe = AdornedElement as FrameworkElement;
            Thumb hitThumb = sender as Thumb;

            if (fxe == null || hitThumb == null)
                return;

            EnforceSize(fxe);

            //Change the size by the amount the user drags the mouse as
            //long as it's larger than the width or height of an adorner, respectively.
            //Also, update the left position by the amount the user drags as long as
            //it's not past the right edge minus the adorner widget width.

            Canvas.SetLeft(fxe, Math.Min((double)Canvas.GetLeft(fxe) + args.HorizontalChange,(double)Canvas.GetLeft(fxe) + fxe.Width - hitThumb.DesiredSize.Width));
            fxe.Width = Math.Max(fxe.Width - args.HorizontalChange, hitThumb.DesiredSize.Width);
            fxe.Height = Math.Max(args.VerticalChange + fxe.Height, hitThumb.DesiredSize.Height);
        }

        //Arrange the Adorners.
        protected override Size ArrangeOverride(Size finalSize)
        {

            //w & h are the width and height of the element
            //that's being adorned.  These will be used to place
            //the Adorner at the corners.  adornerWidth &
            //adornerHeight are used for placement as well.

            double w = AdornedElement.DesiredSize.Width;
            double h = AdornedElement.DesiredSize.Height;
            double adornerWidth = this.DesiredSize.Width;
            double adornerHeight = this.DesiredSize.Height;

            topLeft.Arrange(new Rect(-adornerWidth / 2, -adornerHeight / 2, adornerWidth, adornerHeight));
            topRight.Arrange(new Rect(w - adornerWidth / 2, -adornerHeight / 2, adornerWidth, adornerHeight));
            bottomLeft.Arrange(new Rect(-adornerWidth / 2, h - adornerHeight / 2, adornerWidth, adornerHeight));
            bottomRight.Arrange(new Rect(w - adornerWidth / 2, h -adornerHeight / 2, adornerWidth, adornerHeight));

            //Just using the size that the
            //adorner layer was arranged at.
            return finalSize;

        }

        //Helper code to instantiate the Thumbs, set the
        //Cursor property and add the elements to the
        //Visual tree.

        void BuildAdornerCorner(ref Thumb cornerThumb, Cursor c)
        {
            if (cornerThumb != null) return;
            cornerThumb = new Thumb();
            cornerThumb.Cursor = c;
            VisualOperations.GetChildren(this).Add(cornerThumb);
        }

        //This method ensures that the Widths and Heights
        //are initialized.  Sizing to content produces
        //Width and Height values of Double.NaN.  Because
        //this Adorner explicitly resizes, the Width and Height
        //need to be set first.
        void EnforceSize(FrameworkElement fxe)
        {
            if (fxe.Width.Equals(Double.NaN))
                fxe.Width = fxe.DesiredSize.Width;
            if (fxe.Height.Equals(Double.NaN))
                fxe.Height = fxe.DesiredSize.Height;
        }