C# TaskCompletionSource error when awaiting dependency service

Question

I'm trying to implement TaskCompletionSource to stop code executing until the dependency service method has completed, but am getting an error when trying to return the TaskCompletionSource result

 public interface IImageFetcher<T, K>
 {        
    Task<List<KeyValuePair<T, K>>> GetImageListItems();
 }  

 public Task<List<KeyValuePair<ImageListItem, IosImageModel>>> 
     GetImageListItems()
 {
      var tcs = new 
      TaskCompletionSource<List<KeyValuePair<ImageListItem, 
      IosImageModel>>>();
      .....
      return tcs.SetResult(items);
 }

Call to dependency service:

 List<KeyValuePair<ImageListItem, IosImageModel>> imageListItems = await DependencyService.Get<IImageFetcher<ImageListItem, IosImageModel>>().GetImageListItems();

the line return tcs.SetResult(items) gives an error:

Cannot implicitly convert type 'void' to 'System.Threading.Tasks.Task<System.Collections.Generic.List<System.Collections.Generic.KeyValuePair<Ferret.Models.ImageListItem, Ferret.Models.IosImageModel>>>