A handle assembly, comprising: a mounting assembly comprising a pre-mountable member for mounting on an object and a retractable element, wherein a handle groove is arranged in the pre-mountable member, and the retractable element at least partially extends into the handle groove; and a handle comprising a limiting boss, wherein the limiting boss is configured to be arranged in the handle groove and comprises a limiting groove, and the limiting groove is configured to secure the handle when the retractable element extends into the limiting groove, wherein a clamping slot is arranged on the pre-mountable member and in communication with the handle groove, and the retractable element is configured to move in the clamping slot, and wherein the handle groove has a first and a second limiting step, and the limiting boss is a T-shaped boss and comprises a long boss and a short boss; and wherein the long boss is configured to move in the handle groove, and the short boss is configured to be clamped between the first and second limiting steps when the limiting groove is aligned with the clamping slot, wherein the mounting assembly further comprises an elastic element coupled to the retractable element and configured to push the retractable element towards the handle groove and wherein the retractable element has an inclined guide surface, wherein the inclined guide surface is configured in such a way that the handle presses the inclined guide surface and the retractable element is retracted from the handle groove when the handle moves along the handle groove towards the retractable element, and wherein the retractable element is configured to enter the limiting groove from the clamping slot under an elastic force of the elastic element when the limiting groove is aligned with the clamping slot. a mounting assembly comprising a pre-mountable member for mounting on an object and a retractable element, wherein a handle groove is arranged in the pre-mountable member, and the retractable element at least partially extends into the handle groove; and a handle comprising a limiting boss, wherein the limiting boss is configured to be arranged in the handle groove and comprises a limiting groove, and the limiting groove is configured to secure the handle when the retractable element extends into the limiting groove, wherein a clamping slot is arranged on the pre-mountable member and in communication with the handle groove, and the retractable element is configured to move in the clamping slot, and wherein the handle groove has a first and a second limiting step, and the limiting boss is a T-shaped boss and comprises a long boss and a short boss; and wherein the long boss is configured to move in the handle groove, and the short boss is configured to be clamped between the first and second limiting steps when the limiting groove is aligned with the clamping slot, wherein the mounting assembly further comprises an elastic element coupled to the retractable element and configured to push the retractable element towards the handle groove and wherein the retractable element has an inclined guide surface, wherein the inclined guide surface is configured in such a way that the handle presses the inclined guide surface and the retractable element is retracted from the handle groove when the handle moves along the handle groove towards the retractable element, and wherein the retractable element is configured to enter the limiting groove from the clamping slot under an elastic force of the elastic element when the limiting groove is aligned with the clamping slot.