private void OnEnterPanel(AttachToPanelEvent evt)
 {
     AddFromUrlFieldContainer.RegisterCallback <FocusEvent>(OnContainerFocus);
     AddFromUrlFieldContainer.RegisterCallback <FocusOutEvent>(OnContainerFocusOut);
     UrlTextField.RegisterCallback <FocusEvent>(OnUrlTextFieldFocus);
     UrlTextField.RegisterCallback <FocusOutEvent>(OnUrlTextFieldFocusOut);
     UrlTextField.RegisterCallback <ChangeEvent <string> >(OnUrlTextFieldChange);
     UrlTextField.RegisterCallback <KeyDownEvent>(OnKeyDownShortcut);
     Hide();
 }
        public PackageAddFromUrlField()
        {
            var root = Resources.GetTemplate("PackageAddFromUrlField.uxml");

            Add(root);
            Cache = new VisualElementCache(root);

            AddButton.clickable.clicked += OnAddButtonClick;

            RegisterCallback <MouseDownEvent>(evt => Hide());
            AddFromUrlFieldContainer.RegisterCallback <MouseDownEvent>(evt =>
            {
                EditorApplication.delayCall += () => { UrlTextField.visualInput.Focus(); };
                evt.StopPropagation();
            });

            UrlTextField.RegisterCallback <ChangeEvent <string> >(OnUrlTextFieldChange);
        }