Added TextHelper#cycle to cycle over an array of values on each hit (useful for alternating row colors etc) #2154 [dave-ml@dribin.org]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2213 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

actionpack/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Added TextHelper#cycle to cycle over an array of values on each hit (useful for alternating row colors etc) #2154 [dave-ml@dribin.org]
+
 * Ensure that request.path never returns nil. Closes #1675 [Nicholas Seckar]
 
 * Add ability to specify Route Regexps for controllers. Closes #1917. [Sebastian Kanthak]

actionpack/lib/action_view/helpers/text_helper.rb

@@ -189,9 +189,91 @@ module ActionView
 
         html
       end
+      
+      # Returns a Cycle object whose to_s value cycles through items of an
+      # array every time it is called. This can be used to alternate classes
+      # for table rows:
+      #
+      # <%- for item in @items do -%>
+      #   <tr class="<%= cycle("even", "odd") %>">
+      #     ... use item ...
+      #   </tr>
+      # <%- end -%>
+      #
+      # You can use named cycles to prevent clashes in nested loops.  You'll
+      # have to reset the inner cycle, manually:
+      #
+      # <%- for item in @items do -%>
+      #   <tr class="<%= cycle("even", "odd", :name => "row_class")
+      #     <td>
+      #       <%- for value in item.values do -%>
+      #         <span style="color:'<%= cycle("red", "green", "blue"
+      #                                       :name => "colors") %>'">
+      #           item
+      #         </span>
+      #       <%- end -%>
+      #       <%- reset_cycle("colors") -%>
+      #     </td>
+      #   </tr>
+      # <%- end -%>
+      def cycle(first_value, *values)
+        if (values.last.instance_of? Hash)
+          params = values.pop
+          name = params[:name]
+        else
+          name = "default"
+        end
+        values.unshift(first_value)
+
+        cycle = get_cycle(name)
+        if (cycle.nil? || cycle.values != values)
+          cycle = set_cycle(name, Cycle.new(*values))
+        end
+        return cycle.to_s
+      end
+      
+      # Resets a cycle so that it starts from the first element in the array
+      # the next time it is used.
+      def reset_cycle(name = "default")
+        cycle = get_cycle(name)
+        return if cycle.nil?
+        cycle.reset
+      end
+
+      class Cycle
+        attr_reader :values
+        
+        def initialize(first_value, *values)
+          @values = values.unshift(first_value)
+          reset
+        end
+        
+        def reset
+          @index = 0
+        end
+
+        def to_s
+          value = @values[@index].to_s
+          @index = (@index + 1) % @values.size
+          return value
+        end
+      end
 
       
       private
+        # The cycle helpers need to store the cycles in a place that is
+        # guaranteed to be reset every time a page is rendered, so it
+        # uses an instance variable of ActionView::Base.
+        def get_cycle(name)
+          @_cycles = Hash.new if @_cycles.nil?
+          return @_cycles[name]
+        end
+        
+        def set_cycle(name, cycle_object)
+          @_cycles = Hash.new if @_cycles.nil?
+          @_cycles[name] = cycle_object
+        end
+      
         # Returns a version of the text that's safe to use in a regular expression without triggering engine features.
         def escape_regexp(text)
           text.gsub(/([\\|?+*\/\)\(])/) { |m| "\\#{$1}" }

actionpack/test/template/text_helper_test.rb

@@ -8,6 +8,12 @@ class TextHelperTest < Test::Unit::TestCase
   include ActionView::Helpers::TextHelper
   include ActionView::Helpers::TagHelper
   
+  def setup
+    # This simulates the fact that instance variables are reset every time
+    # a view is rendered.  The cycle helper depends on this behavior.
+    @_cycles = nil if (defined? @_cycles)
+  end
+  
   def test_simple_format
     assert_equal "<p>crazy\n<br /> cross\n<br /> platform linebreaks</p>", simple_format("crazy\r\n cross\r platform linebreaks")
     assert_equal "<p>A paragraph</p>\n\n<p>and another one!</p>", simple_format("A paragraph\n\nand another one!")
@@ -137,4 +143,87 @@ class TextHelperTest < Test::Unit::TestCase
     assert_equal %{href="javascript:bang" <a name='hello'>foo</a>, <span>bar</span>}, result
   end
   
+  def test_cycle_class
+    value = Cycle.new("one", 2, "3")
+    assert_equal("one", value.to_s)
+    assert_equal("2", value.to_s)
+    assert_equal("3", value.to_s)
+    assert_equal("one", value.to_s)
+    value.reset
+    assert_equal("one", value.to_s)
+    assert_equal("2", value.to_s)
+    assert_equal("3", value.to_s)
+  end
+  
+  def test_cycle_class_with_no_arguments
+    assert_raise(ArgumentError) { value = Cycle.new() }
+  end
+
+  def test_cycle
+    assert_equal("one", cycle("one", 2, "3"))
+    assert_equal("2", cycle("one", 2, "3"))
+    assert_equal("3", cycle("one", 2, "3"))
+    assert_equal("one", cycle("one", 2, "3"))
+    assert_equal("2", cycle("one", 2, "3"))
+    assert_equal("3", cycle("one", 2, "3"))
+  end
+  
+  def test_cycle_with_no_arguments
+    assert_raise(ArgumentError) { value = cycle() }
+  end
+  
+  def test_cycle_resets_with_new_values
+    assert_equal("even", cycle("even", "odd"))
+    assert_equal("odd", cycle("even", "odd"))
+    assert_equal("even", cycle("even", "odd"))
+    assert_equal("1", cycle(1, 2, 3))
+    assert_equal("2", cycle(1, 2, 3))
+    assert_equal("3", cycle(1, 2, 3))
+    assert_equal("1", cycle(1, 2, 3))
+  end
+  
+  def test_named_cycles
+    assert_equal("1", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("red", cycle("red", "blue", :name => "colors"))
+    assert_equal("2", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("blue", cycle("red", "blue", :name => "colors"))
+    assert_equal("3", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("red", cycle("red", "blue", :name => "colors"))
+  end
+  
+  def test_default_named_cycle
+    assert_equal("1", cycle(1, 2, 3))
+    assert_equal("2", cycle(1, 2, 3, :name => "default"))
+    assert_equal("3", cycle(1, 2, 3))
+  end
+  
+  def test_reset_cycle
+    assert_equal("1", cycle(1, 2, 3))
+    assert_equal("2", cycle(1, 2, 3))
+    reset_cycle
+    assert_equal("1", cycle(1, 2, 3))
+  end
+  
+  def test_reset_unknown_cycle
+    reset_cycle("colors")
+  end
+  
+  def test_recet_named_cycle
+    assert_equal("1", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("red", cycle("red", "blue", :name => "colors"))
+    reset_cycle("numbers")
+    assert_equal("1", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("blue", cycle("red", "blue", :name => "colors"))
+    assert_equal("2", cycle(1, 2, 3, :name => "numbers"))
+    assert_equal("red", cycle("red", "blue", :name => "colors"))
+  end
+  
+  def test_cycle_no_instance_variable_clashes
+    @cycles = %w{Specialized Fuji Giant}
+    assert_equal("red", cycle("red", "blue"))
+    assert_equal("blue", cycle("red", "blue"))
+    assert_equal("red", cycle("red", "blue"))
+    assert_equal(%w{Specialized Fuji Giant}, @cycles)
+  end
+
 end