C# 添加的拇指未渲染

我想实现从FrameworkElement派生的自己的控件，但添加的子元素不会呈现

我不知道为什么

public class RangeSelection : FrameworkElement
{
    private Thumb thumb = null;

    #region Construction / Destruction

    public RangeSelection()
    {
        this.thumb = new Thumb();
        this.thumb.Width    = 32.0;
        this.thumb.Height   = 32.0;
        this.AddVisualChild(this.thumb);

    }

    #endregion

    protected override Size MeasureOverride(Size availableSize)
    {
        this.thumb.Measure(availableSize);
        return new Size(64.0, 64.0);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        this.thumb.Arrange(new Rect(0, 0, 64.0, 64.0));
        return base.ArrangeOverride(finalSize);
    }
}

---

您需要重写

VisualChildrenCount

属性和

GetVisualChild

方法。大概是这样的：

protected override int VisualChildrenCount
{
    get { return thumb == null ? 0 : 1; }
}

protected override Visual GetVisualChild(int index)
{
    if (_child == null)
    {
        throw new ArgumentOutOfRangeException();
    }

    return _child;
}

如果您想要更多的子元素，您应该使用某种集合来存储子元素，然后返回集合的计数或相应的集合元素