wpf调用外部线程操作ui方法

private void PageLoad(object o)
{
_thisWindow = oas Window;
Thread t = new Thread(delegate()
{
_thisWindow.Dispatcher.Invoke(new Action(delegate()
{
PageLoad();
}));
});
t.Start();
}

private void PageLoad()
{
this.SeletcedItem= "ok";
//do some thing...
}