拖拽时怎么设置当前拖拽项目数

  .onDragStart((event)=>{ 
            let video: UDC.Video = new UDC.Video(); 
            video.videoUri = '/resources/rawfile/01.mp4'; 
            let data: UDC.UnifiedData = new UDC.UnifiedData(video); 
            data.addRecord(video); 
            (event as DragEvent).setData(data); 
            return this.pixelMapBuilder; 
          })