Tips and Tricks

From OpenLaszlo

1 Command-Line Debugging
2 Unsupported Features

Command-Line Debugging

If you are debugging and you want to call lzc directly, and you want to see log messages for just a few specific classes in the console, you can do that, like so:

Create a file named $LPS_HOME/console- debug.properties containing something like this:

log4j.logger.org.openlaszlo.compiler.CanvasCompiler=DEBUG

that is:

log4j.logger.<package or class name>=<loglevel>

In your source code, create a logger for that class, or use the existing logger. CanvasCompiler.java declares:

private static Logger mLogger = Logger.getLogger(CanvasCompiler.class);

Then call methods on mLogger: debug, info, error, warn

mLogger.debug("(debug) Compiling canvas."); 
mLogger.info("(info) Compiling canvas.");
mLogger.error("(error) Compiling canvas.");

Then invoke the compiler with -lp console-debug.properties:

lzc -lp console-debug.properties test/hello.lzx

...and you'll see log messages for the level you specified and higher, for that class or package only.

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Unsupported Features

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Compiler Warnings

In LPS3.0b2: The compiler can already warn when you are making a global assignment, which is almost never what you want to do. The warning is off for now, because I need to add a pragma for silencing it when you actually mean to make a global assignment. But if you want to just proof an app to look for bugs like this, use

 lzc --options warnGlobalAssignments=true <your app>

and sift through the warnings by hand.

Other warnings you can enable in the same fashion:

 warnUnusedLocals -- warns if you declare a local variable and never use it
 warnUnusedParameters -- ditto for function parameters

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Call Profiler

The call profiler generates statistics that can be used to measure the time spent in each function, and to generate a call graph.

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XPath Debugging

These can be handy for XPath debugging:

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Lazy Replication for Seamless scrolling of Images

To obtain smooth scrolling of images using BaseGrid you must alter basegrid.lzx in the LPS source.

First, add <simplelayout axis="y"/> after <view name="rowparent" width="${parent.width}"> on line 94. Second, change "lazy" to "normal" for the replication attribute at line 411.

These changes will allow smooth scrolling of images in a grid. If not modified the grid will lazily load images which will cause them to occasionally not render.

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