InvalidOperationException：无法通过引用设置属性

Question

我有一个Controller类，它应该控制MainForm上对象的外观。 每当我尝试在我的Controller类中更改UserControl的属性（如此处的Opacity）时，它都会失败并显示InvalidOperationException

编辑：这是整个错误消息：

  

WindowsBase.dll中出现'System.InvalidOperationException'类型的异常，但未在用户代码中处理   调用线程无法访问此对象，因为另一个线程拥有它

public partial class MainWindow : Window
{
    private CubeControl _cube; //derived from System.Windows.Control.UserControl

    private CubeController _cubeController;

    public MainWindow()
    {
        InitializeComponent();
        _cubeController = new CubeController(_cube);
    }
} 

这是Controller-class

public class CubeController
{

    /// <summary>A reference to the main cube control</summary>
    private CubeControl _cubeControl;

    public CubeController(CubeControl cubeControl)
    {
        _cubeControl = cubeControl;

        // this fails with an InvalidOperationException
        _cubeControl.Opacity = 0.3;     
    }

我做错了什么？