/* 通过文件夹选择器添加文件夹，并加入FutureAccessList */
private async void AddFolder_Click(object sender, RoutedEventArgs e)
{
var folderPicker = new Windows.Storage.Pickers.FolderPicker();
folderPicker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.Desktop;
folderPicker.FileTypeFilter.Add("*");
Windows.Storage.StorageFolder folder = await folderPicker.PickSingleFolderAsync();
if (folder != null)
{
// Application now has read/write access to all contents in the picked folder
// (including other sub-folder contents)
string token = Windows.Storage.AccessCache.StorageApplicationPermissions.
FutureAccessList.Add(folder);
viewModel.FolderAdd(token, folder.Name, await GetNumInFolder(folder));
// 显示新加入文件夹下的视频
showVideoInFolder(token);
}
}
