def fix(self):
        """
        Fix the block, register all the parameters of sub layers.
        :return:
        """
        if not self.fixed:
            for layer in self.layers:
                if not layer.initialized:
                    raise Exception("All sub layers in a block must be initialized when fixing it.")
                self.register_inner_layers(layer)
            self.fixed = True
Fix the block, register all the parameters of sub layers.
        :return: