C# Drag and Drop Image within Canvas

Question

I tried to Google how to make drag & drop for UIElements on a Canvas, but couldn't find anything that I'm looking for.

I got a C# WPF application with a Window. Inside the Window I got a Canvas where I can add Images to. What I want is to be able to Drag & Drop the Images, while staying within the Canvas' borders. I also want this to be in code, so not in the xaml.

I got this in the function where I add/update the Images to the Canvas. The TODO's should be replaced for the Drag & Drop events.

Image img = ImageList[i].Image;
img.Name = "Image" + i;

// TODO: Drag and Drop event for Image

// TODO: Check if Left and Top are within Canvas (minus width / height of Image) 

Canvas.SetLeft(img, Left); // Default Left when adding the image = 0
Canvas.SetTop(img, Top); // Default Top when adding the image = 0

MyCanvas.Children.Add(img);
OnPropertyChanged("MyCanvas");

PS: Though this is for later, if someone has code to drag and drop multiple images at once as an additional bonus, I would appreciate it.

Thanks in advance for the help.

Answer 1

Fixed my problem below, by using the following code:

img.AllowDrop = true;
img.PreviewMouseLeftButtonDown += this.MouseLeftButtonDown;
img.PreviewMouseMove += this.MouseMove;
img.PreviewMouseLeftButtonUp += this.PreviewMouseLeftButtonUp;


private object movingObject;
private double firstXPos, firstYPos;
private void MouseLeftButtonDown(object sender, MouseButtonEventArgs e) {
    // In this event, we get the current mouse position on the control to use it in the MouseMove event.
    Image img = sender as Image;
    Canvas canvas = img.Parent as Canvas;

    firstXPos = e.GetPosition(img).X;
    firstYPos = e.GetPosition(img).Y;

    movingObject = sender;

    // Put the image currently being dragged on top of the others
    int top = Canvas.GetZIndex(img);
    foreach (Image child in canvas.Children)
        if (top < Canvas.GetZIndex(child))
            top = Canvas.GetZIndex(child);
    Canvas.SetZIndex(img, top + 1);
}
private void PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e) {
    Image img = sender as Image;
    Canvas canvas = img.Parent as Canvas;

    movingObject = null;

    // Put the image currently being dragged on top of the others
    int top = Canvas.GetZIndex(img);
    foreach (Image child in canvas.Children)
        if (top > Canvas.GetZIndex(child))
            top = Canvas.GetZIndex(child);
    Canvas.SetZIndex(img, top + 1);
}
private void MouseMove(object sender, MouseEventArgs e) {
    if (e.LeftButton == MouseButtonState.Pressed && sender == movingObject) {
        Image img = sender as Image;
        Canvas canvas = img.Parent as Canvas;

        double newLeft = e.GetPosition(canvas).X - firstXPos - canvas.Margin.Left;
        // newLeft inside canvas right-border?
        if (newLeft > canvas.Margin.Left + canvas.ActualWidth - img.ActualWidth)
            newLeft = canvas.Margin.Left + canvas.ActualWidth - img.ActualWidth;
        // newLeft inside canvas left-border?
        else if (newLeft < canvas.Margin.Left)
            newLeft = canvas.Margin.Left;
        img.SetValue(Canvas.LeftProperty, newLeft);

        double newTop = e.GetPosition(canvas).Y - firstYPos - canvas.Margin.Top;
        // newTop inside canvas bottom-border?
        if (newTop > canvas.Margin.Top + canvas.ActualHeight - img.ActualHeight)
            newTop = canvas.Margin.Top + canvas.ActualHeight - img.ActualHeight;
        // newTop inside canvas top-border?
        else if (newTop < canvas.Margin.Top)
            newTop = canvas.Margin.Top;
        img.SetValue(Canvas.TopProperty, newTop);
    }
}

This code allows me to drag-and-drop the Images inside the Canvas, without leaving the Canvas itself.

Now I just need to be able to do two more things:

1. Fix a little bug where my Mouse slips of the Image when I drag them around to fast. This happens quite often, even when I'm not even moving the dragging image around THAT fast.. Fixed by using the solution mentioned in my other question.
2. Making it able to drag-and-drop multiple images at once, preferably by selecting multiple first, and then drag-and-drop the whole bunch of them while staying inside the Canvas.

Will make a new Question for this.

Answer 2

I was did a project that uses a chunk of your code and does drag and drop on canvas, look into it and see if there be any difference, dont really have the time to check

private void pinCanvas_PreviewMouseLeftButtonDown_1(object sender, MouseButtonEventArgs e)
        {
         //   Point pt = e.GetPosition(pinCanvas);
         //   Curosor.Text = String.Format("You are at ({0}in, {1}in) in window coordinates", (pt.X / (96 / 72)) * 1/72, (pt.Y / (96 / 72)) * 1/72);
        }
        bool captured = false;
        double x_shape, x_canvas, y_shape, y_canvas;
        UIElement source = null;
        string elementName;
        double elementHeight, elementWidth;
        private void pinCanvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            setCanvasSize();
            source = (UIElement)sender;
            elementName = ((Label)source).Name;
            switch (elementName)
            {
                case "pinTextBox" :
                    elementHeight = pinActualHeight;
                    elementWidth = pinActualWidth;
                    break;
                case "serialTextBox" :
                    elementHeight = serialActualHeight;
                    elementWidth = serialActualWidth;
                    break;
                case "batchTextBox" :
                    elementHeight = batchActualHeight;
                    elementWidth = batchActualWidth;
                    break;
            }
            Mouse.Capture(source);
            captured = true;
            x_shape = Canvas.GetLeft(source);
            x_canvas = e.GetPosition(Maincanvas).X;
            y_shape = Canvas.GetTop(source);
            y_canvas = e.GetPosition(Maincanvas).Y;
        }

        private void pinCanvas_MouseMove(object sender, MouseEventArgs e)
        {
            if (captured)
            {

                double x = e.GetPosition(Maincanvas).X;
                double y = e.GetPosition(Maincanvas).Y;
                var xCond = Math.Round(appActivities.DIP2Inch(x_shape), 4).ToString();
                var yCond = Math.Round(appActivities.DIP2Inch(y_shape), 4).ToString();
                var name = ((Label)source).Name;
                x_shape += x - x_canvas;
            //    if ((x_shape < Maincanvas.ActualWidth - elementWidth) && x_shape > 0)
           //     {
                    Canvas.SetLeft(source, x_shape);
                    switch (name)
                    {
                        case "pinTextBox" :
                            pinOffsetLeft.Text = xCond;
                            break;
                        case "serialTextBox" :
                            serialOffsetLeft.Text = xCond;
                            break;
                        case "batchTextBox" :
                            batchOffsetLeft.Text = xCond;
                            break;
                    }

         //       }
                x_canvas = x;
                y_shape += y - y_canvas;
            //    if (y_shape < Maincanvas.ActualHeight - elementHeight && y_shape > 0)
             //   {
                    Canvas.SetTop(source, y_shape);
                    switch (name)
                    {
                        case "pinTextBox":
                            pinOffsetTop.Text = yCond;
                            break;
                        case "serialTextBox":
                            serialOffsetTop.Text = yCond;
                            break;
                        case "batchTextBox":
                            batchOffsetTop.Text = yCond;
                            break;
                    }

          //      }
                y_canvas = y;
            }
        }

        private void pinCanvas_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            Mouse.Capture(null);
            captured = false;
          //  MessageBox.Show((Canvas.GetTop(source)).ToString());
         /*   if (Canvas.GetTop(source) < 0)
            {
                Canvas.SetTop(source, 0);
            }
            if (Canvas.GetLeft(source) < 0)
            {
                Canvas.SetLeft(source, 0);
            }

            if (Canvas.GetLeft(source) > Maincanvas.ActualWidth - elementWidth)
            {
              //  MessageBox.Show("Left Too Much " + (Canvas.GetLeft(source) * 1/96).ToString());
                Canvas.SetLeft(source, Maincanvas.ActualWidth - elementWidth);
            }

            if (Canvas.GetTop(source) > Maincanvas.ActualHeight - elementHeight)
            {
                Canvas.SetTop(source, Maincanvas.ActualHeight - elementHeight);
            } */
            oneElemntTorched = true;
            //MessageBox.Show(this.pinTextBox.ActualHeight.ToString() + ", " + this.pinTextBox.ActualWidth.ToString());
        }