undefined method `model_name' for NilClass:Clas - ruby-on-rails

Question

I am getting an error in Rails 3.2 with devise - my view is saying undefined method on line 1 below (user). This view is an edit profile page for logged in users.
So far I've tried changing this to current_user and defining that in my controller which I've provided below, but that did not work.
My only other suspicion is that form_for is not appropriate to use on this page?
<%= form_for(#user) do |f| %>
<% if #user.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#user.errors.count, "error") %> prohibited this user from being saved:</h2>
<ul>
<% #user.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :username %><br>
<%= f.text_field :username %>
</div>
<div class="field">
<%= f.label :firstname %><br>
<%= f.text_field :firstname %>
</div>
<div class="field">
<%= f.label :lastname %><br>
<%= f.text_field :lastname %>
My controller... (as I said I tried current_user)
class UsersController < ApplicationController
def current_user
#current_user ||= User.find(session[:user_id])
end
def find
#user = User.new
end
def show
#user = User.find(params[:id])
end
# GET /users
# GET /users.json
def index
#users = User.all
end
# GET /users/1
# GET /users/1.json
# GET /users/new
def new
#user = User.new
end
# GET /users/1/edit
def edit
end
# POST /users
# POST /users.json
def create
#user = User.new(user_params)
respond_to do |format|
if #user.save
format.html { redirect_to #user, notice: 'User was successfully created.' }
format.json { render action: 'show', status: :created, location: #user }
else
format.html { render action: 'new' }
format.json { render json: #user.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /users/1
# PATCH/PUT /users/1.json
def update
respond_to do |format|
if #user.update(user_params)
format.html { redirect_to #user, notice: 'User was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #user.errors, status: :unprocessable_entity }
end
end
end
# DELETE /users/1
# DELETE /users/1.json
def destroy
#user.destroy
respond_to do |format|
format.html { redirect_to users_url }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_user
#user = User.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def user_params
params.require(:user).permit(:username, :firstname, :dateofbirth, :lastname, :gender, :location, :email, :password)
end
end

Answer 1

Devise comes with a current_user helper method. You probably don't want to override that, so I'd recommend removing that method from your controller. In one of my apps I allow users to edit their info and this is my edit method:
def edit
#user = current_user
end