Webdialog - trouble passing array from JS to Ruby

[rvs1977]

hi!

I have a problem passing array from Webdialg (Javascript) to Ruby.

Htmlfile.html

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<script>
var layer_array = [108,190,95];
query = 'skp:get_array@' + layer_array;
window.location.href = query;
</script>


Rubyfile.rb

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my_dialog.add_action_callback("get_array") do |web_dialog,yv_array|
UI.messagebox "YV_array from callback action; " + yv_array
end


In the html/js file its possible to do like this:
alert("first item: " + layer_array[0]);
=> Output: "first item: 108"

Or if I do like this:
alert("all items: " + layer_array);
=> Output: "all items: 108,190,95"

Every things work fine!

But, when its send back to ruby the trouble starts:
If I write:
UI.messagebox ("first item: " + layer_array[0])
=> Output: "first item: 57"

But if I write:
UI.messagebox ("all items: " + layer_array)
=> Output: "all items: 108,190,95"
Here it seems to work???

My guess is when its send from JS to Ruby it goes from being an array to be a string?

Anyone know how to overcome this problem?

-Rasmus

[Aerilius]

The webdialog returns a string, for example "[1,2,3]". In Ruby, you always need to have a clear idea what type your value has. In JavaScript, you can mix incompatible types hoping that it will convert it and work as expected, but not in Ruby.
Don't miss to read the Ruby Newbies Getting Started Guide

If you apply an index to a string, you get the character code of the character at that index, example
"string"[0] = 115 # corresponds to 's'

When you later added a string + the arraystring, you got the expected result because both were strings. You can't add an array to a string, because it would give:
Error: #<TypeError: (eval):151:in `+': can't convert Array into String>
The + method is not defined for different types. It exists separately for Numeric, for Strings and for Arrays, and if you have different types, you have to convert them into the same so that you can use one of the methods for it (either with array.to_s or array.inspect).


You could either parse the string into an array for example

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@yv_width_array_rs = yv_width_rs[1..-2].split(",")

which returns an array of strings.
If it should be floats (or integers) then you loop over the resulting array with collect and convert each string of a float into a float with to_f:

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@yv_width_array_rs = yv_width_rs.scan(/\d+/).collect{|d| d.to_f} # or d.to_i

Or you eval the array

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begin
  @yv_width_array_rs = eval(yv_width_rs)
rescue
  @yv_width_array_rs = []
end

which you should absolutely avoid if there is an alternative way.

[Dan Rathbun]

First of all... using UI.messagebox as a debugging tool is a bad idea.
They often fail silently, if the message argument is not correct, or there are Type mismatches in the expression.

Get in the habit on opening the Ruby Console, and using puts() to output debug strings.

And you can use the .to_s() or .inspect() methods to be sure the output is String compatible:

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my_dialog.add_action_callback("get_array") do |web_dialog,yv_array|
  puts "YV_array from callback action; " + yv_array.inspect
end

Also the double-quoted String parameter replacement notation, #{expression}, has built-in text conversion for many Ruby base classes.

So this may also work:

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my_dialog.add_action_callback("get_array") do |web_dialog,yv_array|
  puts "YV_array from callback action: #{yv_array}"
end

[Dan Rathbun]

If I am right the webdialog returns a string, for example "[1,2,3]"
...
Or you eval the array ...

Yup you are correct, and eval() is the simplest way.. provided that on the Js side, you build the strings so Ruby's eval() can read them.

Your JavaScript in the webdialog will invoke the callback method with a string representing arguments to the callback method.

[Dan Rathbun]

Make sure to read by Thomas Thomassen (ThomThom)

PDF download: WebDialogs - The Lost Manual — R1 09 November 2009

SCF Forum Post: WebDialogs - The Lost Manual — R1 09 November 2009

[thomthom]

When you experience trouble with Ruby <-> JavaScript check the compiled string you send backwards and forwards. You will when quickly see syntax errors.

[rvs1977]

Thank you all!! Now I have something to try out.

[Dan Rathbun]

Or you eval the array

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begin
  @yv_width_array_rs = eval(yv_width_rs)
rescue
  @yv_width_array_rs = []
end

Here's a good place to show, how to use the rescue keyword, in modifier position (and save 4 lines of code.)

@yv_width_array_rs = eval(yv_width_rs) rescue []

[rvs1977]

Aerilius, Im a little impressed.

When you quote my code, you use different variable-names than the ones from my example.
The funny thing is, the variable-names you use is the one I actually use on my own computer, before I started to look at arrays... Are you psychic or something??

[Aerilius]

I'm not psychic but rather impressed/surprised myself. That are the variable names that you posted and after submitting my response, you had modified/improved the original question that I didn't recognize it anymore

[rvs1977]

ah ok

Anyway, it finally works with this "simple" solution:

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my_dialog.add_action_callback("get_array") do |web_dialog,yv_array|
@YV_array = yv_array.scan(/\d+/).collect {|d| d.to_i}
end


I wonder why the eval-rescue solution has to be avoided? Is it slow?

Thanks to all of you. - Aerilius, Dan, Thomthom

----------------
Gratias Ad Omnes

[Dan Rathbun]

I wonder why the eval-rescue solution has to be avoided? Is it slow?

ALL String operations in Ruby 1.8.x are slow.

eval() is the Ruby code parser.. so it is a very large method (actually a C-side function.)

But I cannot see it being slower than the 2 iterator methods you are using, in addition to the type converter.

But it works... and you understand how it works. If speed is not an issue, then go with it ...



Also if you KNEW each numeric was separated by a "," then you also do:

@YV_array = yv_array.split(',').map{|i| i.to_i}