C# Drag & Drop Multiple Images within Canvas

问题

I've got the following code to drag and drop images inside my Canvas:

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..
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.

PS: My previously question can be found here.

回答1:

You'll want to lock the mouse on to the image to stop the cursor slipping off it Mouse.Capture (imageReference), you can release it on mouse up with Mouse.Capture (null) – Andy Feb 18 at 15:58

After using Andy's suggestion, by adding:

Mouse.Capture(img);

at the bottom of the MouseLeftButtonDown-function, and

Mouse.Capture(null);

at the bottom of the PreviewMouseLeftButtonUp-function, it works like a charm. So thanks a lot Andy!

来源：https://stackoverflow.com/questions/21857929/c-sharp-drag-drop-multiple-images-within-canvas