more pooling of widgets, rename and rework a few things

ui/util/widgetcache.go

@@ -1,50 +0,0 @@
-package util
-
-import (
-	"time"
-
-	"fyne.io/fyne/v2"
-)
-
-type WidgetType string
-
-const (
-	WidgetTypeAlbumPageHeader  WidgetType = "AlbumPageHeader"
-	WidgetTypeArtistPageHeader WidgetType = "ArtistPageHeader"
-)
-
-type WidgetCache struct {
-	cache map[WidgetType][]cachedWidget
-}
-
-type cachedWidget struct {
-	widget     fyne.CanvasObject
-	releasedAt int64 // unixMillis
-}
-
-func NewWidgetCache() WidgetCache {
-	return WidgetCache{
-		cache: make(map[WidgetType][]cachedWidget),
-	}
-}
-
-func (w *WidgetCache) Obtain(typ WidgetType) fyne.CanvasObject {
-	var widget fyne.CanvasObject
-	if ws, ok := w.cache[typ]; ok && len(ws) > 0 {
-		i := len(ws) - 1
-		widget = ws[i].widget
-		ws[i].widget = nil
-		w.cache[typ] = ws[:i]
-	}
-	return widget
-}
-
-func (w *WidgetCache) Release(typ WidgetType, wid fyne.CanvasObject) {
-	if _, ok := w.cache[typ]; !ok {
-		w.cache[typ] = make([]cachedWidget, 0)
-	}
-	w.cache[typ] = append(w.cache[typ], cachedWidget{
-		widget:     wid,
-		releasedAt: time.Now().UnixMilli(),
-	})
-}

ui/util/widgetpool.go

@@ -0,0 +1,60 @@
+package util
+
+import (
+	"time"
+
+	"fyne.io/fyne/v2"
+)
+
+type WidgetType int
+
+const (
+	WidgetTypeAlbumPageHeader WidgetType = iota
+	WidgetTypeArtistPageHeader
+	WidgetTypePlaylistPageHeader
+	WidgetTypeTracklist
+)
+
+// A pool to share commonly-used widgets across pages to reduce
+// creation of new widgets and memory allocations.
+// It is not thread-safe, which is fine for its current use.
+type WidgetPool struct {
+	cache map[WidgetType][]cachedWidget
+}
+
+type cachedWidget struct {
+	widget     fyne.CanvasObject
+	releasedAt int64 // unixMillis
+}
+
+func NewWidgetPool() WidgetPool {
+	return WidgetPool{
+		cache: make(map[WidgetType][]cachedWidget),
+	}
+}
+
+// Obtain obtains a widget of the given type from the pool, if one exists.
+// Returns nil if there is no available widget.
+func (w *WidgetPool) Obtain(typ WidgetType) fyne.CanvasObject {
+	var widget fyne.CanvasObject
+	if ws, ok := w.cache[typ]; ok && len(ws) > 0 {
+		i := len(ws) - 1
+		widget = ws[i].widget
+		ws[i].widget = nil
+		w.cache[typ] = ws[:i]
+	}
+	return widget
+}
+
+// Release releases a widget into the pool.
+// The widget must not be modified by the releaser after release,
+// since it may be Obtained for a new use at any time.
+func (w *WidgetPool) Release(typ WidgetType, wid fyne.CanvasObject) {
+	if _, ok := w.cache[typ]; !ok {
+		w.cache[typ] = make([]cachedWidget, 0)
+	}
+	w.cache[typ] = append(w.cache[typ], cachedWidget{
+		widget:     wid,
+		releasedAt: time.Now().UnixMilli(),
+	})
+}