add OnScroll event to list

widget/list.go

@@ -37,6 +37,11 @@ type List struct {
 	UpdateItem   func(id ListItemID, item fyne.CanvasObject) `json:"-"`
 	OnSelected   func(id ListItemID)                         `json:"-"`
 	OnUnselected func(id ListItemID)                         `json:"-"`
+	// OnFocused fire an event when a listItem is focused
+	// Whenever the list loses focus ListItemId will be equals to -1
+	//
+	// Since: 2.6
+	OnFocused func(id ListItemID) `json:"-"`
 
 	// HideSeparators hides the separators between list rows
 	//
@@ -107,13 +112,15 @@ func (l *List) FocusGained() {
 	l.focused = true
 	l.scrollTo(l.currentFocus)
 	l.RefreshItem(l.currentFocus)
+	l.onFocused(l.currentFocus)
 }
 
 // FocusLost is called after this List has lost focus.
 //
 // Implements: fyne.Focusable
 func (l *List) FocusLost() {
 	l.focused = false
+	l.onFocused(-1)
 	l.RefreshItem(l.currentFocus)
 }
 
@@ -305,6 +312,7 @@ func (l *List) TypedKey(event *fyne.KeyEvent) {
 		}
 		l.RefreshItem(l.currentFocus)
 		l.currentFocus++
+		l.onFocused(l.currentFocus)
 		l.scrollTo(l.currentFocus)
 		l.RefreshItem(l.currentFocus)
 	case fyne.KeyUp:
@@ -313,6 +321,7 @@ func (l *List) TypedKey(event *fyne.KeyEvent) {
 		}
 		l.RefreshItem(l.currentFocus)
 		l.currentFocus--
+		l.onFocused(l.currentFocus)
 		l.scrollTo(l.currentFocus)
 		l.RefreshItem(l.currentFocus)
 	}
@@ -859,3 +868,9 @@ func createItemAndApplyThemeScope(f func() fyne.CanvasObject, scope fyne.Widget)
 	item.Refresh()
 	return item
 }
+
+func (l *List) onFocused(id ListItemID) {
+	if f := l.OnFocused; f != nil {
+		f(id)
+	}
+}

widget/list_test.go

@@ -75,6 +75,30 @@
 	assert.True(t, resizeCountAllGreaterOrEqual)
 }
 
+func TestList_OnFocused(t *testing.T) {
+	l, _, rows := setupList(t)
+	var selectedId widget.ListItemID
+	l.OnFocused = func(id widget.ListItemID) {
+		selectedId = id
+	}
+	l.FocusGained()
+	assert.Equal(t, selectedId, 0)
+	l.FocusLost()
+	assert.Equal(t, selectedId, -1)
+	l.TypedKey(&fyne.KeyEvent{Name: fyne.KeyDown})
+	assert.Equal(t, selectedId, 1)
+	l.TypedKey(&fyne.KeyEvent{Name: fyne.KeyUp})
+	assert.Equal(t, selectedId, 0)
+	for index, _ := range rows {
+		l.TypedKey(&fyne.KeyEvent{Name: fyne.KeyDown})
+		assert.Equal(t, selectedId, index+1)
+	}
+	for index, _ := range rows {
+		l.TypedKey(&fyne.KeyEvent{Name: fyne.KeyUp})
+		assert.Equal(t, selectedId, len(rows)-(index+1))
+	}
+}
+
 func setupList(t *testing.T) (*widget.List, fyne.Window, []*resizeRefreshCountingLabel) {
 	var rows []*resizeRefreshCountingLabel
 	test.NewTempApp(t)