Microsoft.Practices.ServiceLocation.ActivationException

我正在尝试使用ServiceLocator 创建一个实例

/// <summary>
/// Gets the MediaPlayer property.
/// </summary>
[SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification = "This non-static member is needed for data binding purposes.")]
public MediaPlayerViewModel MediaPlayer
{
    get
    {
        try
        {
            return ServiceLocator.Current.GetInstance<MediaPlayerViewModel>();
        }
        catch (Exception e)
        {
            System.Console.WriteLine(e.ToString());
            return null;
        }
    }
}

但我得到了以下解释：

Microsoft.Practices.ServiceLocation.ActivationException未处理按用户代码HResult=-2146233088消息=发生激活错误在尝试获取MediaPlayerViewModel类型的实例时，键"
Source=Microsoft.Practices.ServiceLocation StackTrace:位于Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstance（类型serviceType，字符串键）c： ''Projects''CommonServiceLocator''man''Microsoft.Practices.ServiceLocation''ServiceLocatorImplBase.cs:line53位于Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstanceTService在里面c： ''Projects''CommonServiceLocator''man''Microsoft.Practices.ServiceLocation''ServiceLocatorImplBase.cs:line90位于Verint.PI2.MediaPlayer.UI.ViewModel.ViewModelLocator.get_MediaPlayer（）在c:''Users''ekreiczer''Documents''Visual Studio中2012''Projects''player''Verint.PI2.MediaPlayer.UI''ViewModel''ViewModelLocator.cs:line73内部异常：Microsoft.Practices.Unity.ResolutionFailedExceptionHResult=-2146233088消息=解析依赖项失败，类型="Verint.PI2.MediaPlayer.UI.ViewModel.MediaPlayerViewModel"，名称="（无）"。解析时发生异常。例外情况是：InvalidOperationException-当前类型，Verint.PI2.MediaPlayer.UI.Services.IDialogService，是一个接口和无法构建。您是否缺少类型映射？

我不知道怎么打地图，有人能帮忙吗？