appDisplay: Add moveItem()

This is a handy function to implement changing an icon's position
in the grid.

WIP: better commit message

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/603

js/ui/appDisplay.js

@@ -163,6 +163,28 @@ class BaseAppView {
         this.emit('view-loaded');
     }
 
+    moveItem(item, newPosition) {
+        let itemIndex = this._allItems.indexOf(item);
+
+        if (itemIndex == -1) {
+            log('Trying to move item %s that is not in this app view'.format(item.id));
+            return;
+        }
+
+        let visibleItems = this._allItems.filter(item => item.actor.visible);
+        let visibleIndex = visibleItems.indexOf(item);
+        if (newPosition > visibleIndex)
+            newPosition -= 1;
+
+        // Remove from the old position
+        this._allItems.splice(itemIndex, 1);
+
+        let realPosition = this._grid.moveItem(item, newPosition);
+        this._allItems.splice(realPosition, 0, item);
+
+        return realPosition;
+    }
+
     _selectAppInternal(id) {
         if (this._items[id])
             this._items[id].actor.navigate_focus(null, St.DirectionType.TAB_FORWARD, false);

js/ui/iconGrid.js

@@ -695,6 +695,22 @@ var IconGrid = GObject.registerClass({
             this.add_actor(item.actor);
     }
 
+    moveItem(item, newPosition) {
+        if (!this.contains(item.actor)) {
+            log('Cannot move item not contained by the IconGrid');
+            return;
+        }
+
+        let children = this.get_children();
+        let visibleChildren = children.filter(c => c.is_visible());
+        let visibleChildAtPosition = visibleChildren[newPosition];
+        let realPosition = children.indexOf(visibleChildAtPosition);
+
+        this.set_child_at_index(item.actor, realPosition);
+
+        return realPosition;
+    }
+
     removeItem(item) {
         this.remove_child(item.actor);
     }