Silverlight 3（在其上构建Windows Phone 7框架）不支持MultiBinding，这是你将用来实现你所需要的。但是，有一个解决方案解决方案，您可以使用在 MultiBinding for Sivlerlight 3 中的描述也可以使用WP7。

Silverlight 3 (on which the Windows Phone 7 framework is built) doesn't support MultiBinding, which is what you would use to achieve what you need. However, there is a workaround solution that you can use described in the post MultiBinding for Sivlerlight 3, which should also work on WP7.

或者，您可以扩展视图模型（或至少是您所暴露的属性），以显示一个聚合值并引发的属性财产变更通知，当更改。

Alternatively, you could extend your view model (or at least the properties that you are exposing) to expose a property that aggregates your values and raises property change notification when either changes.