aboutsummaryrefslogtreecommitdiffstats
path: root/actionview/lib/action_view/layouts.rb
blob: 1fc609f2cd7ec53cda1b725f020a360288e9b8d7 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
require "action_view/rendering"
require "active_support/core_ext/module/remove_method"

module ActionView
  # Layouts reverse the common pattern of including shared headers and footers in many templates to isolate changes in
  # repeated setups. The inclusion pattern has pages that look like this:
  #
  #   <%= render "shared/header" %>
  #   Hello World
  #   <%= render "shared/footer" %>
  #
  # This approach is a decent way of keeping common structures isolated from the changing content, but it's verbose
  # and if you ever want to change the structure of these two includes, you'll have to change all the templates.
  #
  # With layouts, you can flip it around and have the common structure know where to insert changing content. This means
  # that the header and footer are only mentioned in one place, like this:
  #
  #   // The header part of this layout
  #   <%= yield %>
  #   // The footer part of this layout
  #
  # And then you have content pages that look like this:
  #
  #    hello world
  #
  # At rendering time, the content page is computed and then inserted in the layout, like this:
  #
  #   // The header part of this layout
  #   hello world
  #   // The footer part of this layout
  #
  # == Accessing shared variables
  #
  # Layouts have access to variables specified in the content pages and vice versa. This allows you to have layouts with
  # references that won't materialize before rendering time:
  #
  #   <h1><%= @page_title %></h1>
  #   <%= yield %>
  #
  # ...and content pages that fulfill these references _at_ rendering time:
  #
  #    <% @page_title = "Welcome" %>
  #    Off-world colonies offers you a chance to start a new life
  #
  # The result after rendering is:
  #
  #   <h1>Welcome</h1>
  #   Off-world colonies offers you a chance to start a new life
  #
  # == Layout assignment
  #
  # You can either specify a layout declaratively (using the #layout class method) or give
  # it the same name as your controller, and place it in <tt>app/views/layouts</tt>.
  # If a subclass does not have a layout specified, it inherits its layout using normal Ruby inheritance.
  #
  # For instance, if you have PostsController and a template named <tt>app/views/layouts/posts.html.erb</tt>,
  # that template will be used for all actions in PostsController and controllers inheriting
  # from PostsController.
  #
  # If you use a module, for instance Weblog::PostsController, you will need a template named
  # <tt>app/views/layouts/weblog/posts.html.erb</tt>.
  #
  # Since all your controllers inherit from ApplicationController, they will use
  # <tt>app/views/layouts/application.html.erb</tt> if no other layout is specified
  # or provided.
  #
  # == Inheritance Examples
  #
  #   class BankController < ActionController::Base
  #     # bank.html.erb exists
  #
  #   class ExchangeController < BankController
  #     # exchange.html.erb exists
  #
  #   class CurrencyController < BankController
  #
  #   class InformationController < BankController
  #     layout "information"
  #
  #   class TellerController < InformationController
  #     # teller.html.erb exists
  #
  #   class EmployeeController < InformationController
  #     # employee.html.erb exists
  #     layout nil
  #
  #   class VaultController < BankController
  #     layout :access_level_layout
  #
  #   class TillController < BankController
  #     layout false
  #
  # In these examples, we have three implicit lookup scenarios:
  # * The BankController uses the "bank" layout.
  # * The ExchangeController uses the "exchange" layout.
  # * The CurrencyController inherits the layout from BankController.
  #
  # However, when a layout is explicitly set, the explicitly set layout wins:
  # * The InformationController uses the "information" layout, explicitly set.
  # * The TellerController also uses the "information" layout, because the parent explicitly set it.
  # * The EmployeeController uses the "employee" layout, because it set the layout to nil, resetting the parent configuration.
  # * The VaultController chooses a layout dynamically by calling the <tt>access_level_layout</tt> method.
  # * The TillController does not use a layout at all.
  #
  # == Types of layouts
  #
  # Layouts are basically just regular templates, but the name of this template needs not be specified statically. Sometimes
  # you want to alternate layouts depending on runtime information, such as whether someone is logged in or not. This can
  # be done either by specifying a method reference as a symbol or using an inline method (as a proc).
  #
  # The method reference is the preferred approach to variable layouts and is used like this:
  #
  #   class WeblogController < ActionController::Base
  #     layout :writers_and_readers
  #
  #     def index
  #       # fetching posts
  #     end
  #
  #     private
  #       def writers_and_readers
  #         logged_in? ? "writer_layout" : "reader_layout"
  #       end
  #   end
  #
  # Now when a new request for the index action is processed, the layout will vary depending on whether the person accessing
  # is logged in or not.
  #
  # If you want to use an inline method, such as a proc, do something like this:
  #
  #   class WeblogController < ActionController::Base
  #     layout proc { |controller| controller.logged_in? ? "writer_layout" : "reader_layout" }
  #   end
  #
  # If an argument isn't given to the proc, it's evaluated in the context of
  # the current controller anyway.
  #
  #   class WeblogController < ActionController::Base
  #     layout proc { logged_in? ? "writer_layout" : "reader_layout" }
  #   end
  #
  # Of course, the most common way of specifying a layout is still just as a plain template name:
  #
  #   class WeblogController < ActionController::Base
  #     layout "weblog_standard"
  #   end
  #
  # The template will be looked always in <tt>app/views/layouts/</tt> folder. But you can point
  # <tt>layouts</tt> folder direct also. <tt>layout "layouts/demo"</tt> is the same as <tt>layout "demo"</tt>.
  #
  # Setting the layout to nil forces it to be looked up in the filesystem and fallbacks to the parent behavior if none exists.
  # Setting it to nil is useful to re-enable template lookup overriding a previous configuration set in the parent:
  #
  #     class ApplicationController < ActionController::Base
  #       layout "application"
  #     end
  #
  #     class PostsController < ApplicationController
  #       # Will use "application" layout
  #     end
  #
  #     class CommentsController < ApplicationController
  #       # Will search for "comments" layout and fallback "application" layout
  #       layout nil
  #     end
  #
  # == Conditional layouts
  #
  # If you have a layout that by default is applied to all the actions of a controller, you still have the option of rendering
  # a given action or set of actions without a layout, or restricting a layout to only a single action or a set of actions. The
  # <tt>:only</tt> and <tt>:except</tt> options can be passed to the layout call. For example:
  #
  #   class WeblogController < ActionController::Base
  #     layout "weblog_standard", except: :rss
  #
  #     # ...
  #
  #   end
  #
  # This will assign "weblog_standard" as the WeblogController's layout for all actions except for the +rss+ action, which will
  # be rendered directly, without wrapping a layout around the rendered view.
  #
  # Both the <tt>:only</tt> and <tt>:except</tt> condition can accept an arbitrary number of method references, so
  # #<tt>except: [ :rss, :text_only ]</tt> is valid, as is <tt>except: :rss</tt>.
  #
  # == Using a different layout in the action render call
  #
  # If most of your actions use the same layout, it makes perfect sense to define a controller-wide layout as described above.
  # Sometimes you'll have exceptions where one action wants to use a different layout than the rest of the controller.
  # You can do this by passing a <tt>:layout</tt> option to the <tt>render</tt> call. For example:
  #
  #   class WeblogController < ActionController::Base
  #     layout "weblog_standard"
  #
  #     def help
  #       render action: "help", layout: "help"
  #     end
  #   end
  #
  # This will override the controller-wide "weblog_standard" layout, and will render the help action with the "help" layout instead.
  module Layouts
    extend ActiveSupport::Concern

    include ActionView::Rendering

    included do
      class_attribute :_layout, :_layout_conditions, :instance_accessor => false
      self._layout = nil
      self._layout_conditions = {}
      _write_layout_method
    end

    delegate :_layout_conditions, to: :class

    module ClassMethods
      def inherited(klass) # :nodoc:
        super
        klass._write_layout_method
      end

      # This module is mixed in if layout conditions are provided. This means
      # that if no layout conditions are used, this method is not used
      module LayoutConditions # :nodoc:
        private

        # Determines whether the current action has a layout definition by
        # checking the action name against the :only and :except conditions
        # set by the <tt>layout</tt> method.
        #
        # ==== Returns
        # * <tt>Boolean</tt> - True if the action has a layout definition, false otherwise.
        def _conditional_layout?
          return unless super

          conditions = _layout_conditions

          if only = conditions[:only]
            only.include?(action_name)
          elsif except = conditions[:except]
            !except.include?(action_name)
          else
            true
          end
        end
      end

      # Specify the layout to use for this class.
      #
      # If the specified layout is a:
      # String:: the String is the template name
      # Symbol:: call the method specified by the symbol, which will return the template name
      # false::  There is no layout
      # true::   raise an ArgumentError
      # nil::    Force default layout behavior with inheritance
      #
      # ==== Parameters
      # * <tt>layout</tt> - The layout to use.
      #
      # ==== Options (conditions)
      # * :only   - A list of actions to apply this layout to.
      # * :except - Apply this layout to all actions but this one.
      def layout(layout, conditions = {})
        include LayoutConditions unless conditions.empty?

        conditions.each {|k, v| conditions[k] = Array(v).map(&:to_s) }
        self._layout_conditions = conditions

        self._layout = layout
        _write_layout_method
      end

      # Creates a _layout method to be called by _default_layout .
      #
      # If a layout is not explicitly mentioned then look for a layout with the controller's name.
      # if nothing is found then try same procedure to find super class's layout.
      def _write_layout_method # :nodoc:
        remove_possible_method(:_layout)

        prefixes    = _implied_layout_name =~ /\blayouts/ ? [] : ["layouts"]
        default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}).first || super"
        name_clause = if name
          default_behavior
        else
          <<-RUBY
            super
          RUBY
        end

        layout_definition = case _layout
          when String
            _layout.inspect
          when Symbol
            <<-RUBY
              #{_layout}.tap do |layout|
                return #{default_behavior} if layout.nil?
                unless layout.is_a?(String) || !layout
                  raise ArgumentError, "Your layout method :#{_layout} returned \#{layout}. It " \
                    "should have returned a String, false, or nil"
                end
              end
            RUBY
          when Proc
            define_method :_layout_from_proc, &_layout
            protected :_layout_from_proc
            <<-RUBY
              result = _layout_from_proc(#{_layout.arity == 0 ? '' : 'self'})
              return #{default_behavior} if result.nil?
              result
            RUBY
          when false
            nil
          when true
            raise ArgumentError, "Layouts must be specified as a String, Symbol, Proc, false, or nil"
          when nil
            name_clause
        end

        if self._layout_conditions.empty?
          self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
            def _layout
              #{layout_definition}
            end
            private :_layout
          RUBY
        else
          self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
            def _layout
              if _conditional_layout?
                #{layout_definition}
              else
                #{name_clause}
              end
            end
            private :_layout
          RUBY
        end
      end

      private

      # If no layout is supplied, look for a template named the return
      # value of this method.
      #
      # ==== Returns
      # * <tt>String</tt> - A template name
      def _implied_layout_name # :nodoc:
        controller_path
      end
    end

    def _normalize_options(options) # :nodoc:
      super

      if _include_layout?(options)
        layout = options.delete(:layout) { :default }
        options[:layout] = _layout_for_option(layout)
      end
    end

    attr_internal_writer :action_has_layout

    def initialize(*) # :nodoc:
      @_action_has_layout = true
      super
    end

    # Controls whether an action should be rendered using a layout.
    # If you want to disable any <tt>layout</tt> settings for the
    # current action so that it is rendered without a layout then
    # either override this method in your controller to return false
    # for that action or set the <tt>action_has_layout</tt> attribute
    # to false before rendering.
    def action_has_layout?
      @_action_has_layout
    end

  private

    def _conditional_layout?
      true
    end

    # This will be overwritten by _write_layout_method
    def _layout; end

    # Determine the layout for a given name, taking into account the name type.
    #
    # ==== Parameters
    # * <tt>name</tt> - The name of the template
    def _layout_for_option(name)
      case name
      when String     then _normalize_layout(name)
      when Proc       then name
      when true       then Proc.new { _default_layout(true)  }
      when :default   then Proc.new { _default_layout(false) }
      when false, nil then nil
      else
        raise ArgumentError,
          "String, Proc, :default, true, or false, expected for `layout'; you passed #{name.inspect}"
      end
    end

    def _normalize_layout(value)
      value.is_a?(String) && value !~ /\blayouts/ ? "layouts/#{value}" : value
    end

    # Returns the default layout for this controller.
    # Optionally raises an exception if the layout could not be found.
    #
    # ==== Parameters
    # * <tt>require_layout</tt> - If set to true and layout is not found,
    #   an ArgumentError exception is raised (defaults to false)
    #
    # ==== Returns
    # * <tt>template</tt> - The template object for the default layout (or nil)
    def _default_layout(require_layout = false)
      begin
        value = _layout if action_has_layout?
      rescue NameError => e
        raise e, "Could not render layout: #{e.message}"
      end

      if require_layout && action_has_layout? && !value
        raise ArgumentError,
          "There was no default layout for #{self.class} in #{view_paths.inspect}"
      end

      _normalize_layout(value)
    end

    def _include_layout?(options)
      (options.keys & [:body, :text, :plain, :html, :inline, :partial]).empty? || options.key?(:layout)
    end
  end
end