Simple Row Style Alternator
In your view (rhtml):
[code lang="xml"]| Name |
|---|
| <%= user.name %> |
In your helper (rb): Updated!
[code lang="ruby"] def row_style @row_index ||= 0 @row_index += 1 @row_index % 2 == 0 ? "Even" : "Odd" end [/code] Latest ZooDotCom
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10 comments
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10.21.05 @ 05:24
Odo said...
- Small and useful. Thanx.
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10.21.05 @ 07:27
Forrest said...
-
Could you re-write the first line of your helper method as such?
@row_index |= 0
Just trying to firm up some of my understanding of Ruby.
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10.21.05 @ 08:04
Jason said...
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Forrest,
Almost – you’ll want two pipes, as in ||=
irb(main):001:0> foo = 0 if !foo
=> 0
irb(main):002:0> foo = 1 if !foo
=> nil
irb(main):003:0> foo
=> 0
irb(main):004:0> bar ||= 0
=> 0
irb(main):005:0> bar ||= 1
=> 0
I’m still trying to learn Ruby, too – I think it works as follows:
a |= 0 expands to a = a | 0.
b ||= 0 expands to b = b || 0.
The | operator evaluates the two operands as boolean values and returns true if either is true (not short-circuiting). Seems most anything except nil and false eval to true here, including 0. I’m pretty sure on this, but can’t find a reference to corroborate it.
The || operator returns the first operand if it evaluates to true; otherwise it returns the second operand. So, given b = b || 0, if b is nil, (b || 0) returns 0.
Can a Ruby expert step in and confirm/clarify?
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10.21.05 @ 08:23
Forrest said...
-
Jason,
You are correct. The ||= performs what I was thinking of. I didn’t even run |= through irb. Guess I should do that from now on :o) The ||= operator is also explained in the “Agile Web Development With Rails” book on page 479. Thanks for the correction and help.
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10.21.05 @ 11:03
M@ said...
- Nice! Thanks for the suggestion, I’ll update the post to show this approach.
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10.21.05 @ 11:49
protocool said...
-
Good idea for a helper.
Alack, there’s a hidden gotcha if you happen to have more than one zebra list in the current scope. I know, I know, it’s seems strange to have more than one list on a page but hey, I’m sure somebody is doing it
Anyhow the gotcha is that you can’t reset @row_index to 0 except for in the template itself and that exposes the guts of your helper function in unpleasant ways.
How about something like this:
def row_style(opt = :row_style)
case opt
when Fixnum
return opt % 2 0 ? 'Even' : 'Odd'
when Symbol
val = instance_variable_get("@#{opt.id2name}_counter") || 1
instance_variable_set("@#{opt.id2name}_counter", val + 1)
return val % 2 0 ? ‘Even’ : ‘Odd’
else
raise ArgumentError, “row_style: descriptive error message here”
end
end
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10.22.05 @ 00:35
Stephen Waits said...
-
def row_style
row_index = 1 - (row_index ||= 0)
@row_index == 0 ? “Even” : “Odd”
end
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10.27.05 @ 13:36
Will Rogers said...
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Re: protocool
You are thinking too hard.
def row_style(key = :default)
row_indices ||= {}row_indices[key] = 1 – (
row_indices[key] ||= 0)row_indices[key] == 0 ? “even” : “odd”
end
with thanks to Stephen for the clever linecount compression ;)
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01.20.06 @ 14:06
Ben Marini said...
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There’s a rails function for this now:
“>
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01.20.06 @ 14:07
Ben Marini said...
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Whoops.
cycle(‘even’,‘odd’) is what I meant to say. Check it out in the rails api.
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