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Pager for lots o' data

/ Published in: Ruby
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This function (intended to be an application or view helper) creates a pager bar useful for navigating many pages. It shows the first, last, current, nearby, and halfway-to-end pages. It looks like this (where the current page is 11):

< 1 ... 5 ... 10 11 12 ... 14 15 >

The pagerBar function takes two parameters: a RoR paginator, and an anchor that will be attached to all the links.

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  1. class ActionController::AbstractRequest
  2.   def get_post_params
  3.     self.parameters.reject {|k,v| k == 'controller' || k == 'action'}
  4.   end
  5. end
  6.  
  7. def pagerBar(paginator, anchor)
  8.   page = paginator.current_page;
  9.   pageParam = 'page';
  10.   firstPage = 1;
  11.   lastPage = paginator.page_count;
  12.   prevStr = '←';
  13.   nextStr = '→';
  14.   elideStr = '… ';   # Include trailing space.
  15.   pageSpan = 3;      # How many pages to the left and right of current.
  16.  
  17.   # The central group of pages.
  18.   window = page.window(pageSpan);
  19.   windowFirst = window.first.number;
  20.   windowLast = window.last.number;
  21.  
  22.   # These define the halfway pages.
  23.   prevHalfway = (windowFirst / 2.0).floor;
  24.   prevHalfway = 2 if prevHalfway == 1;
  25.   nextHalfway = ((windowLast + lastPage) / 2.0).ceil;
  26.   nextHalfway = lastPage - 1 if nextHalfway == lastPage;
  27.  
  28.   # Need to show first/last pages separate from range?
  29.   showFirst = (windowFirst > 1);
  30.   showLast = (windowLast < lastPage);
  31.  
  32.   # Need to show half-way pages?
  33.   showPrevHalfway = (prevHalfway > 1 && prevHalfway < windowFirst);
  34.   showNextHalfway = (nextHalfway < lastPage && nextHalfway > windowLast);
  35.  
  36.   # Pages missing before/after half-way pages?
  37.   elideBeforePrevHalf = (showPrevHalfway && (prevHalfway - firstPage) > 1);
  38.   elideAfterPrevHalf = (showPrevHalfway && (windowFirst - prevHalfway) > 1);
  39.   elideBeforeNextHalf = (showNextHalfway && (nextHalfway - windowLast) > 1);
  40.   elideAfterNextHalf = (showNextHalfway && (lastPage - nextHalfway) > 1);
  41.  
  42.   # No half-way pages, but pages missing before/after range?
  43.   elideBeforeRange = (!showPrevHalfway && (windowFirst - firstPage) > 1);
  44.   elideAfterRange = (!showNextHalfway && (lastPage - windowLast) > 1);
  45.  
  46.   # Do prev arrow.
  47.   html = link_to_unless(page.first?, prevStr,
  48.     request.get_post_params.merge(
  49.       { pageParam => page.previous, :anchor => anchor }));
  50.   html += ' ';
  51.  
  52.   # Do first page.
  53.   if (showFirst)
  54.     html += link_to(paginator.first_page.number.to_s,
  55.       request.get_post_params.merge(
  56.         { pageParam => paginator.first_page.number, :anchor => anchor }));
  57.     html += ' ';
  58.   end
  59.  
  60.   # Do prev halfway point.
  61.   html += elideStr if elideBeforePrevHalf;
  62.   if (showPrevHalfway)
  63.     html += link_to(paginator[prevHalfway].number.to_s,
  64.       request.get_post_params.merge(
  65.         { pageParam => paginator[prevHalfway].number, :anchor => anchor }));
  66.     html += ' ';
  67.   end
  68.   html += elideStr if elideAfterPrevHalf;
  69.  
  70.   # Do range.
  71.   html += elideStr if elideBeforeRange;
  72.   window.pages.each do |windowPage|
  73.     html += link_to_unless (page == windowPage, windowPage.number.to_s,
  74.       request.get_post_params.merge(
  75.         { pageParam => windowPage.number, :anchor => anchor }));
  76.     html += ' ';
  77.   end
  78.   html += elideStr if elideAfterRange;
  79.  
  80.   # Do next halfway point.
  81.   html += elideStr if elideBeforeNextHalf;
  82.   if (showNextHalfway)
  83.     html += link_to(paginator[nextHalfway].number.to_s,
  84.       request.get_post_params.merge(
  85.         { pageParam => paginator[nextHalfway].number, :anchor => anchor }));
  86.     html += ' ';
  87.   end
  88.   html += elideStr if elideAfterNextHalf;
  89.  
  90.   # Do last page.
  91.   if (showLast)
  92.     html += link_to(paginator.last_page.number.to_s,
  93.       request.get_post_params.merge(
  94.         { pageParam => paginator.last_page.number, :anchor => anchor }));
  95.     html += ' ';
  96.   end
  97.  
  98.   # Do next arrow.
  99.   html += link_to_unless(page.last?, nextStr,
  100.     request.get_post_params.merge(
  101.       { pageParam => page.next, :anchor => anchor }));
  102.  
  103.   # Return
  104.   html
  105. end

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