Add error message and disabling of preview button

src/coffee/controllers/item_page_controller.coffee

@@ -166,7 +166,6 @@ module.exports = class ItemPageController extends PageController
                     @model.item.description = ''
 
                 @_descriptionController.model = @model.item.description
-                @_descriptionController.loadImages()
 
     _endEditingDescription: ->
         oldDescription = @model.item.description

src/coffee/controllers/markdown_image_controller.coffee

@@ -89,6 +89,12 @@ module.exports = class MarkdownImageController extends BaseController
             @$loading.hide duration:Duration.normal
             @$loaded.show duration:Duration.normal, queue:true
 
+        if @model.status is MarkdownImage.Status.empty
+            @$errorMessage.html 'please choose an image'
+            @$errorContainer.show duration:Duration.normal
+        else
+            @$errorContainer.hide duration:Duration.normal
+
         super
 
     # Backbone.View Overrides ######################################################################

src/coffee/controllers/markdown_image_list_controller.coffee

@@ -20,15 +20,13 @@ module.exports = class MarkdownImageListController extends BaseController
         super options
 
         @imageBase = ''
+        @_valid = null
 
     # Public Methods ###############################################################################
 
     getImageUrlForFile: (fileName)->
         @model.getImageUrlForFile fileName
 
-    loadImages: ->
-        @model.loadImages()
-
     reset: ->
         @model.reset()
 
@@ -51,17 +49,27 @@ module.exports = class MarkdownImageListController extends BaseController
     setMarkdownText: (markdownText)->
         @model.markdownText = markdownText
 
+    getValid: ->
+        return @_valid
+
     Object.defineProperties @prototype,
         imageBase:    {get:@prototype.getImageBase,    set:@prototype.setImageBase}
         markdownText: {get:@prototype.getMarkdownText, set:@prototype.setMarkdownText}
+        valid:        {get:@prototype.getValid}
 
     # BaseController Overrides #####################################################################
 
+    onDidModelChange: ->
+        super
+        @_setValid @model.valid
+
     onDidRender: ->
         @$imageContainer = @$('.image_container')
         super
 
     refresh: ->
+        @model.loadImages()
+
         @_controllers ?= []
         index = 0
 
@@ -79,3 +87,14 @@ module.exports = class MarkdownImageListController extends BaseController
 
         while @_controllers.length > index
             @_controllers.pop().remove()
+
+    # Private Methods ##############################################################################
+
+    _setValid: (newValid)->
+        oldValid = @_valid
+        return if newValid is oldValid
+
+        @_valid = newValid
+        logger.debug "setting mic.valid to #{@_valid}"
+        @trigger Event.change + ':valid', this, oldValid, newValid
+        @trigger Event.change

src/coffee/controllers/markdown_section_controller.coffee

@@ -54,9 +54,6 @@ module.exports = class MarkdownSectionController extends BaseController
 
     # Public Methods ###############################################################################
 
-    loadImages: ->
-        @_imageListController.loadImages()
-
     resetToDefaultState: ->
         if @model?
             @state = State.viewing
@@ -157,9 +154,12 @@ module.exports = class MarkdownSectionController extends BaseController
             client: @client
             imageBase: @imageBase
         @on Event.change + ':imageBase', => @_imageListController.model.imageBase = @imageBase
+        @listenTo @_imageListController, Event.change + ':valid', => @tryRefresh()
 
         @$errorText     = @$('.error p')
         @$markdownPanel = @$('.markdown')
+        @$previewButton = @$('button.preview')
+        @$saveButton    = @$('button.save')
         @$sizer         = @$('.sizer')
         @$textarea      = @$('textarea')
         @$title         = @$('h2')
@@ -172,6 +172,7 @@ module.exports = class MarkdownSectionController extends BaseController
         @$title.html @title
         @_imageListController.markdownText = @model
 
+        @_updateButtonStates()
         @_updateSizer()
         @_updatePreview()
         super
@@ -208,6 +209,14 @@ module.exports = class MarkdownSectionController extends BaseController
 
             return result
 
+    _updateButtonStates: ->
+        for $button in [ @$previewButton, @$saveButton ]
+            logger.debug "updating buttons based upon valid state: #{@_imageListController.valid}"
+            if @_imageListController.valid
+                $button.prop 'disabled', false
+            else
+                $button.prop 'disabled', true
+
     _updateSizer: ->
         text = @model
         if @model?
@@ -239,9 +248,9 @@ module.exports = class MarkdownSectionController extends BaseController
             errorPanel:        @$('.error')
             imageList:         @$('.image_list')
             markdownPanel:     @$markdownPanel
-            previewButton:     @$('button.preview')
+            previewButton:     @$previewButton
             returnButton:      @$('button.return')
-            saveButton:        @$('button.save')
+            saveButton:        @$saveButton
             waitingPanel:      @$('.waiting')
 
         visible = {}