的问题是，一个的UIElement 只能属于以一次一个家长。为了增加您的物品进入根画布，你需要首先从 Template_canvas1 画布删除它们。

The problem is, that a UIElement can only belong to one parent at a time. In order to add your items into the root canvas, you need to first remove them from the Template_canvas1 canvas.

请参阅下面的代码。我创建的数组 UI元素复制，然后把它们添加到 Template_canvas1 删除C>根。

See the following code. I create an array of the UIElements to copy, and then remove them from Template_canvas1 before adding them to root.

private void add_template_Click(object sender, RoutedEventArgs e)
{
    var childrenList = Template_canvas1.Children.Cast<UIElement>().ToArray();
    root.Children.Clear();
    foreach (var c in childrenList)
    {
        Template_canvas1.Children.Remove(c);
        root.Children.Add(c);
    }
}

还有一个选择，如果你不这样做要从中删除 Template_canvas1 的项目，你可以创建UI元素的深层复制。另请参见下面的，我不会从 Template_canvas1 删除的项目：

There is one more option, if you don't want to remove the items from Template_canvas1, you can create a Deep Copy of the UIElements. See also the following where I do not remove the items from Template_canvas1:

private void add_template_Click(object sender, RoutedEventArgs e)
{
    root.Children.Clear();
    foreach (UIElement child in Template_canvas1.Children)
    {
        var xaml = System.Windows.Markup.XamlWriter.Save(child);
        var deepCopy = System.Windows.Markup.XamlReader.Parse(xaml) as UIElement;
        root.Children.Add(deepCopy);
    }
}