fix #37: infinite scroll stops loading if scrolling immediately to bottom

ui/widgets/albumgrid.go

@@ -29,6 +29,7 @@ type AlbumGrid struct {
 type AlbumGridState struct {
 	albums       []*subsonic.AlbumID3
 	iter         *backend.BatchingIterator
+	highestShown int
 	fetching     bool
 	done         bool
 	showYear     bool
@@ -136,6 +137,9 @@ func (ag *AlbumGrid) createGridWrapList() {
 }
 
 func (ag *AlbumGrid) doUpdateAlbumCard(albumIdx int, ac *AlbumCard) {
+	if albumIdx > ag.highestShown {
+		ag.highestShown = albumIdx
+	}
 	album := ag.albums[albumIdx]
 	if ac.PrevAlbumID == album.ID {
 		// nothing to do
@@ -171,18 +175,22 @@ func (ag *AlbumGrid) doUpdateAlbumCard(albumIdx int, ac *AlbumCard) {
 		ac.ImgLoadCancel = cancel
 	}
 
-	// TODO: remove magic number 10
+	// if user has scrolled near the bottom, fetch more
 	if !ag.done && !ag.fetching && albumIdx > len(ag.albums)-10 {
 		ag.fetchMoreAlbums(20)
 	}
 }
 
+// fetches at least count more albums
 func (a *AlbumGrid) fetchMoreAlbums(count int) {
 	if a.iter == nil {
 		a.done = true
 	}
 	a.fetching = true
 	go func() {
+		// keep repeating the fetch task as long as the user
+		// has scrolled near the bottom
+		for !a.done && a.highestShown >= len(a.albums)-10 {
 			n := 0
 			for !a.done && n < count {
 				albums := a.iter.NextN(albumFetchBatchSize)
@@ -195,6 +203,7 @@ func (a *AlbumGrid) fetchMoreAlbums(count int) {
 					a.Refresh()
 				}
 			}
+		}
 		a.fetching = false
 	}()
 }