Few improvements to FormPreview, thanks Andy!

This commit adds several new hooks in backwards-compatible way:
 * get_initial to specify initial data based on request
 * get_auto_id to enable different AUTO_ID values
 * get_context for overriding and extending default context contents

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14659 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/formtools/preview.py

@@ -51,15 +51,15 @@ class FormPreview(object):
 
     def preview_get(self, request):
         "Displays the form"
-        f = self.form(auto_id=AUTO_ID)
+        f = self.form(auto_id=self.get_auto_id(), initial=self.get_initial(request))
         return render_to_response(self.form_template,
-            {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state},
+            self.get_context(request, f),
             context_instance=RequestContext(request))
 
     def preview_post(self, request):
         "Validates the POST data. If valid, displays the preview page. Else, redisplays form."
-        f = self.form(request.POST, auto_id=AUTO_ID)
-        context = {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state}
+        f = self.form(request.POST, auto_id=self.get_auto_id())
+        context = self.get_context(request, f)
         if f.is_valid():
             self.process_preview(request, f, context)
             context['hash_field'] = self.unused_name('hash')
@@ -91,7 +91,7 @@ class FormPreview(object):
 
     def post_post(self, request):
         "Validates the POST data. If valid, calls done(). Else, redisplays form."
-        f = self.form(request.POST, auto_id=AUTO_ID)
+        f = self.form(request.POST, auto_id=self.get_auto_id())
         if f.is_valid():
             if not self._check_security_hash(request.POST.get(self.unused_name('hash'), ''),
                                              request, f):
@@ -99,11 +99,30 @@ class FormPreview(object):
             return self.done(request, f.cleaned_data)
         else:
             return render_to_response(self.form_template,
-                {'form': f, 'stage_field': self.unused_name('stage'), 'state': self.state},
+                self.get_context(request, f),
                 context_instance=RequestContext(request))
 
     # METHODS SUBCLASSES MIGHT OVERRIDE IF APPROPRIATE ########################
 
+    def get_auto_id(self):
+        """
+        Hook to override the ``auto_id`` kwarg for the form. Needed when
+        rendering two form previews in the same template.
+        """
+        return AUTO_ID
+
+    def get_initial(self, request):
+        """
+        Takes a request argument and returns a dictionary to pass to the form's
+        ``initial`` kwarg when the form is being created from an HTTP get.
+        """
+        return {}
+
+    def get_context(self, request, form):
+        "Context for template rendering."
+        return {'form': form, 'stage_field': self.unused_name('stage'), 'state': self.state}
+
+
     def parse_params(self, *args, **kwargs):
         """
         Given captured args and kwargs from the URLconf, saves something in

django/contrib/formtools/tests/__init__.py

@@ -11,6 +11,13 @@ success_string = "Done was called!"
 
 
 class TestFormPreview(preview.FormPreview):
+    def get_context(self, request, form):
+        context = super(TestFormPreview, self).get_context(request, form)
+        context.update({'custom_context': True})
+        return context
+
+    def get_initial(self, request):
+        return {'field1': 'Works!'}
 
     def done(self, request, cleaned_data):
         return http.HttpResponse(success_string)
@@ -59,6 +66,8 @@ class PreviewTests(TestCase):
         response = self.client.get('/test1/')
         stage = self.input % 1
         self.assertContains(response, stage, 1)
+        self.assertEquals(response.context['custom_context'], True)
+        self.assertEquals(response.context['form'].initial, {'field1': 'Works!'})
 
     def test_form_preview(self):
         """