c# - 拖动用户控件，但将其保留在 WPF 中其父级的范围内

Question

我有一个用户控件，我正在将其拖到网格内。 Z-Index 设置得相当高，这样我就可以将它保持在其他 child 之上。拖动控件效果很好，但如果用户想将控件移到网格之外，它会允许。

我如何防止它离开父网格控件的边界，这是我现在拥有的:

   private System.Windows.Point _anchorPoint;
    private System.Windows.Point _currentPoint;
    private bool _isInDrag;

   private void UserControl_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var element = sender as FrameworkElement;
        _anchorPoint = e.GetPosition(null);
        if (element != null) element.CaptureMouse();
        _isInDrag = true;
        e.Handled = true;
    }

    private void UserControl_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        if (!_isInDrag) return;
        var element = sender as FrameworkElement;
        if (element != null) element.ReleaseMouseCapture();
        _isInDrag = false;
        e.Handled = true;
    }

   private void UserControl_MouseMove(object sender, MouseEventArgs e)
        {
            if (!_isInDrag) return;
            _currentPoint = e.GetPosition(null);

            UIElement container = VisualTreeHelper.GetParent(_parentGrid) as UIElement;
            System.Windows.Point relativeLocation = _parentGrid.TranslatePoint(new System.Windows.Point(0, 0), container);

            if (_currentPoint.X > relativeLocation.X) return;
            if(_currentPoint.Y >= relativeLocation.Y)return;

            _transform.X += _currentPoint.X - _anchorPoint.X;
            _transform.Y += (_currentPoint.Y - _anchorPoint.Y);
            RenderTransform = _transform;
            _anchorPoint = _currentPoint;
        }

“relativeLocation”始终为 0x0，因此无法正常工作。任何想法将不胜感激。

*注意:我知道如果我将 UserControl 更改为 Window，它会减轻我遇到的所有问题。但老实说，这样看起来很棒，我真的不想把 window 弄得乱七八糟。该系统作为仪表板打开，占据用户的整个窗口(在单独的窗口中打开)。所以当你在这里打开一个窗口时，它不会正确流动。

Answer 1

我认为您不需要 relativeLocation。不过，数学可能有点烦人。试试这个方法，我测试的时候效果很好:

    private void UserControl_MouseMove(object sender, MouseEventArgs e)
    {
        if (!_isInDrag) return;
        _currentPoint = e.GetPosition(null);

        //This is the change to the position that we want to apply
        Point delta = new Point();
        delta.X = _currentPoint.X - _anchorPoint.X;
        delta.Y = _currentPoint.Y - _anchorPoint.Y;

        //Calculate user control edges
        var leftEdge   = Margin.Left + _transform.X + delta.X;
        var topEdge    = Margin.Top + _transform.Y + delta.Y;
        var rightEdge  = Width + Margin.Left + _transform.X + delta.X;
        var bottomEdge = Height + Margin.Top + _transform.Y + delta.Y;

        //Set the delta to 0 if it goes over _parentGrid edges
        if (leftEdge < 0) delta.X = 0;
        if (topEdge  < 0) delta.Y = 0;

        if (rightEdge  > _parentGrid.Width)  delta.X = 0;
        if (bottomEdge > _parentGrid.Height) delta.Y = 0;

        //Apply the delta to the user control
        _transform.X += delta.X;
        _transform.Y += delta.Y;
        RenderTransform = _transform;
        _anchorPoint = _currentPoint;
    }