C#实现操作ppt使屏幕自动无限循环播放指定幻灯片

各位老师好 想写个软件 使电脑自动播放ppt 幻灯片 无限循环播放 。现在自动播放已经实现 但是无法自动循环。求教如何修改
public void PPTAuto(string filePath, int playTime) //输入要播放的ppt文件和播放间隔时间
        {  
            //防止连续打开多个PPT程序.
            if (this.objApp != null)
            { return; }
            objApp = new POWERPOINT.Application();
            objPresSet = objApp.Presentations.Open(filePath, OFFICECORE.MsoTriState.msoCTrue, OFFICECORE.MsoTriState.msoFalse, OFFICECORE.MsoTriState.msoFalse); 
            // 自动播放的代码（开始）      
            int Slides = objPresSet.Slides.Count;
            int[] SlideIdx = new int[Slides];
            for (int i = 0; i < Slides; i++) 
            { SlideIdx[i] = i + 1; }; 
            objSldRng = objPresSet.Slides.Range(SlideIdx);
            objSST = objSldRng.SlideShowTransition;      
            //设置翻页的时间.
            objSST.AdvanceOnTime = OFFICECORE.MsoTriState.msoCTrue;
            objSST.AdvanceTime = playTime;     
            //翻页时的特效! 
            objSST.EntryEffect = POWERPOINT.PpEntryEffect.ppEffectCircleOut;
            //Prevent Office Assistant from displaying alert messages:      
            bAssistantOn = objApp.Assistant.On;
            objApp.Assistant.On = false;     
            //Run the Slide show from slides 1 thru 3.
            objSSS = objPresSet.SlideShowSettings;
            objSSS.StartingSlide = 1; 
            objSSS.EndingSlide = Slides;
            objSSS.Run(); 
            //Wait for the slide show to end.
            objSSWs = objApp.SlideShowWindows;
            while (objSSWs.Count >= 1) System.Threading.Thread.Sleep(playTime * 100);
            this.objPresSet.Close(); 
            this.objApp.Quit();  
        }