Fix issue #368 where opening a screen twice from the same parent would cause a crash.

Rakefile

@@ -10,3 +10,12 @@ Motion::Project::App.setup do |app|
   app.device_family = [ :ipad ] # so we can test split screen capability
   app.detect_dependencies = true
 end
+
+namespace :spec do
+  task :unit do
+    App.config.spec_mode = true
+    spec_files = App.config.spec_files - Dir.glob('./spec/functional/**/*.rb')
+    App.config.instance_variable_set("@spec_files", spec_files)
+    Rake::Task["simulator"].invoke
+  end
+end

lib/ProMotion/screen/screen_navigation.rb

@@ -70,6 +70,7 @@ module ProMotion
         PM.logger.error "You need a nav_bar if you are going to push #{vc.to_s} onto it."
       end
       nav_controller ||= self.navigationController
+      return if nav_controller.topViewController == vc
       vc.first_screen = false if vc.respond_to?(:first_screen=)
       nav_controller.pushViewController(vc, animated: animated)
     end

spec/unit/screen_helpers_spec.rb

@@ -212,6 +212,20 @@ describe "screen helpers" do
         screen.should == new_screen
       end
 
+      it "should not double-open a view controller if it's already been opened" do
+        parent_screen = HomeScreen.new(nav_bar: true)
+        new_screen = BasicScreen.new
+        @pushed = 0
+        parent_screen.navigationController.mock!("pushViewController:animated:") do |vc, animated|
+          @pushed += 1
+          parent_screen.navigationController.stub!("topViewController", return: vc)
+        end
+        parent_screen.open new_screen
+        @pushed.should == 1
+        parent_screen.open new_screen
+        @pushed.should == 1
+      end
+
     end