Empty Handlers in OpenLaszlo 4.1

The current release of OpenLaszlo doesn’t like empty handler tags. If you compile the following code, you’ll get a compiler warning:

<canvas debug="true">
    <handler name="oninit">

    </handler>
</canvas>

The warning will say:

“Refusing to compile an empty handler, you should declare the event instead”

This wasn’t the case previously. The warning is intended to educate developers who continue to define empty handlers to “hack” a custom event. (This is an old practice that is no longer necessary, since there is now an <event /> tag). If you’re intentionally writing empty handler tags (e.g. as stubs), those warnings may get in the way.

To work around them, provide a comment in your empty handler:

<canvas debug="true">
    <handler name="oninit">
        // Setup code for application.
    </handler>
</canvas>

Installing RMagick on Cygwin

RMagick is a Ruby to ImageMagick framework that’s needed if you want to edit images using Rails. FileColumn, a Rails plugin for handling file uploads, plugs into RMagick very smoothly. While FileColumn is really simple to use, installing RMagick on Cygwin seemed really daunting. There were a bunch of warnings on how it differs from a usual Rails plugin install. So I’m summarizing my experience here:

  1. First install ImageMagick for Cygwin. Do this by updating Cygwin itself, using the Cygwin setup program. It’s the same approach as you use for installing Cygwin the first time around. When you get to the Select Packages page, find the ImageMagick packages under the Graphics node and make sure they’re set to be installed. Look for libImageMagick1; there are a few others.
  2. Run gem update –system
  3. Download the RMagick gem for Linux. Not the Win32 one. That’s the one called “rmagick”. You have to download it; you can’t install it remotely.
  4. From the directory where you downloaded the RMagick gem, run gem install rmagick –local
  5. Rebase Cygwin. I’ve never had to do this before, but I got a bunch of errors in the Ruby server output console saying the following when RMagick was used:
    unable to remap C:\cygwin\usr\X11R6\bin\cygXext-6.dll to same address ruby died waiting for dll loading, errno 11
    To rebase Cygwin, close all your Cygwin shells, and open an ash shell by going to Start>Run…, then enter C:\cygwin\bin\ash.exe in the Run dialog and click OK. Run /bin/rebaseall from the ash console.

Then restart the Rails server from script.

For reference, I used RMagick 2.5.2, with Ruby 1.8.2 and Rails 2.1.0.

Using the form_for Method with multipart in Rails

If you’re going to upload files via an HTML form, the form’s encoding must be set to multipart/form-data. In Rails, you use a helper method to generate the form tags, so you can’t directly edit them. The preferred helper is form_for; that’s what scaffold generates.

Normally, a form_for call would look like this:

<% form_for(@entry) do |f| %>
  <!-- Form fields -->
<% end %>

To make this form be multipart, change the call to the following:

<% form_for(@entry, :html => {:multipart => true}) do |f| %>
  <!-- Form fields -->
<% end %>