begin reuse of widgets across pages

ui/util/widgetcache.go

@@ -0,0 +1,50 @@
+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(),
+	})
+}