A method for producing a contact lens, comprising the steps of: obtaining a contact lens precursor which has a concave surface and an opposite convex surface and comprises a lens bulk material and first reactive functional groups on and/or near the anterior and posterior surfaces, wherein the first reactive functional groups are selected from the group consisting of carboxyl groups, amino groups, azetidnium groups, epoxide groups, aziridine groups, vinylsulfone groups, thiol groups, and combinations thereof; placing the contact lens precursor in a container in a position to ensure that the concave surface of the contact lens precursor faces up whereas the convex surface faces down; dosing an aqueous solution into the concave surface of the contact lens precursor in an amount for immersing completely the contact lens precursor in the aqueous solution in the container while maintaining the concave surface facing up, wherein the aqueous solution has a room temperature and comprises at least one hydrophilic polymeric material, wherein said at least one hydrophilic polymeric material comprises second reactive functional groups each of which is capable of reacting with one first reactive functional group at a temperature above the room temperature to form a covalent linkage, wherein the second reactive functional groups are selected from the group consisting of carboxyl groups, amino groups, azetidinium groups, epoxide groups, aziridine groups, vinylsulfone groups, thiol groups, and combinations thereof; and increasing the temperature of the aqueous solution with the contact lens precursor therein to a temperature of from 35°C to 140°C to form the contact lens that comprises the lens bulk material covered with an outer surface hydrogel layer, wherein the outer surface hydrogel layer consists of an anterior outer hydrogel layer and a posterior outer hydrogel layer, wherein the outer posterior surface hydrogel layer is softer than the outer anterior surface hydrogel layer as characterized by having a ratio of indentation depth, Id PS Id AS, of at least about 1.2, wherein ( Id) PS is the indentation depth measured with a indenting probe having a tip radius of 9.5 μm and a stiffness of 0.54 N/m at 5 KPa compression pressure against the posterior surface in a nanoindentation test, wherein ( Id) AS is the indentation depth measured with a indenting probe having a tip radius of 9.5 μm and a stiffness of 0.54 N/m at 5 KPa compression pressure against the anterior surface in a nanoindentation test, wherein the contact lens has a water-break-up time of at least 10 seconds. obtaining a contact lens precursor which has a concave surface and an opposite convex surface and comprises a lens bulk material and first reactive functional groups on and/or near the anterior and posterior surfaces, wherein the first reactive functional groups are selected from the group consisting of carboxyl groups, amino groups, azetidnium groups, epoxide groups, aziridine groups, vinylsulfone groups, thiol groups, and combinations thereof; placing the contact lens precursor in a container in a position to ensure that the concave surface of the contact lens precursor faces up whereas the convex surface faces down; dosing an aqueous solution into the concave surface of the contact lens precursor in an amount for immersing completely the contact lens precursor in the aqueous solution in the container while maintaining the concave surface facing up, wherein the aqueous solution has a room temperature and comprises at least one hydrophilic polymeric material, wherein said at least one hydrophilic polymeric material comprises second reactive functional groups each of which is capable of reacting with one first reactive functional group at a temperature above the room temperature to form a covalent linkage, wherein the second reactive functional groups are selected from the group consisting of carboxyl groups, amino groups, azetidinium groups, epoxide groups, aziridine groups, vinylsulfone groups, thiol groups, and combinations thereof; and increasing the temperature of the aqueous solution with the contact lens precursor therein to a temperature of from 35°C to 140°C to form the contact lens that comprises the lens bulk material covered with an outer surface hydrogel layer, wherein the outer surface hydrogel layer consists of an anterior outer hydrogel layer and a posterior outer hydrogel layer, wherein the outer posterior surface hydrogel layer is softer than the outer anterior surface hydrogel layer as characterized by having a ratio of indentation depth, Id PS Id AS, of at least about 1.2, wherein ( Id) PS is the indentation depth measured with a indenting probe having a tip radius of 9.5 μm and a stiffness of 0.54 N/m at 5 KPa compression pressure against the posterior surface in a nanoindentation test, wherein ( Id) AS is the indentation depth measured with a indenting probe having a tip radius of 9.5 μm and a stiffness of 0.54 N/m at 5 KPa compression pressure against the anterior surface in a nanoindentation test, wherein the contact lens has a water-break-up time of at least 10 seconds.