C# 将控件/UI元素限制在屏幕边界内

我有一个

Canvas

作为我的应用程序的基础，它有几个控件，用户可以使用各自的

操作delta

来移动、旋转和缩放

问题在于，当用户用手指移动控件时，可能会意外地将控件移出

画布

或屏幕边界

如何限制这些控件在

画布中的移动？
您可以检查控件和WinRT XAML工具包中的灵感

总的来说，这是相当基本的。如果不做惯性，可能是这样的：

if (x < 0)
    x = 0;
if (x > _canvas.ActualWidth - this.AssociatedObject.ActualWidth)
    x = _canvas.ActualWidth - this.AssociatedObject.ActualWidth;
if (y < 0)
    y = 0;
if (y > _canvas.ActualHeight - this.AssociatedObject.ActualHeight)
    y = _canvas.ActualHeight - this.AssociatedObject.ActualHeight;

一旦获得边界矩形-您可以使用其尺寸，而不是操纵对象的实际宽度

/

实际高度

和X&Y来确定其可以或不能移动的位置。

是，当控件与屏幕边界对齐时，该操作有效。但是，当控件旋转一个角度时，将

实际宽度

添加到

x

中，其中x是左上角点，不会给出右上角点。

/// <summary>
/// Gets the bounding rectangle of a given element
/// relative to a given other element or visual root
/// if relativeTo is null or not specified.
/// </summary>
/// <remarks>
/// Note that the bounding box is calculated based on the corners of the element relative to itself,
/// so e.g. a bounding box of a rotated ellipse will be larger than necessary and in general
/// bounding boxes of elements with transforms applied to them will often be calculated incorrectly.
/// </remarks>
/// <param name="dob">The starting element.</param>
/// <param name="relativeTo">The relative to element.</param>
/// <returns></returns>
/// <exception cref="System.InvalidOperationException">Element not in visual tree.</exception>
public static Rect GetBoundingRect(this FrameworkElement dob, FrameworkElement relativeTo = null)
{
    if (DesignMode.DesignModeEnabled)
    {
        return Rect.Empty;
    }

    if (relativeTo == null)
    {
        relativeTo = Window.Current.Content as FrameworkElement;
    }

    if (relativeTo == null)
    {
        throw new InvalidOperationException("Element not in visual tree.");
    }

    if (dob == relativeTo)
    {
        return new Rect(0, 0, relativeTo.ActualWidth, relativeTo.ActualHeight);
    }

    var ancestors = dob.GetAncestors().ToArray();

    if (!ancestors.Contains(relativeTo))
    {
        throw new InvalidOperationException("Element not in visual tree.");
    }

    var topLeft =
        dob
            .TransformToVisual(relativeTo)
            .TransformPoint(new Point());
    var topRight =
        dob
            .TransformToVisual(relativeTo)
            .TransformPoint(
                new Point(
                    dob.ActualWidth,
                    0));
    var bottomLeft =
        dob
            .TransformToVisual(relativeTo)
            .TransformPoint(
                new Point(
                    0,
                    dob.ActualHeight));
    var bottomRight =
        dob
            .TransformToVisual(relativeTo)
            .TransformPoint(
                new Point(
                    dob.ActualWidth,
                    dob.ActualHeight));

    var minX = new[] { topLeft.X, topRight.X, bottomLeft.X, bottomRight.X }.Min();
    var maxX = new[] { topLeft.X, topRight.X, bottomLeft.X, bottomRight.X }.Max();
    var minY = new[] { topLeft.Y, topRight.Y, bottomLeft.Y, bottomRight.Y }.Min();
    var maxY = new[] { topLeft.Y, topRight.Y, bottomLeft.Y, bottomRight.Y }.Max();

    return new Rect(minX, minY, maxX - minX, maxY - minY);
}