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LWUIT Project Administration Technical Issues Resources

LWUIT Project Administration

Q: Where can I learn about LWUIT?

Try the tutorial the blog and the forum there are also several articles and the developer guide which is a part of the LWUIT drops.

Q: How do I get the LWUIT source code? Binaries?

The source code is only available via SVN, if you don't know how to use SVN please research the internet for instructions on that subject.
Binaries are released periodically without a specific schedule and are available as LWUIT drops.

Q: I have a problem/question regarding LWUIT what should I do?

First search the forum and the issue tracker, if the answer isn't covered you can post a question to the forum. Make sure to use the CURRENT SVN only! Questions regarding drops are problematic since they force us to recall long resolved issues.
If you wish to file an issue/RFE (also required to provide attachements) use the issue tracker, it requires you to be a project member. Make sure to only request observer role! All other role requests are automatically regected!
Before filing an issue make sure you provide code which can be used standalone to reproduce the problem against the current SVN.
See the following question about contribution.

Q: How do I contribute to LWUIT?

By signing the SCA and emailing a scanned version to lwuit (at) as explained in the LWUIT-incubator project. Please do not send source code for inclusion in LWUIT without signing this document first.

Q: Is LWUIT free for commercial use? Obfuscating? What Licesne?

The source is under the GPL + Class Path Exception, the binary drops are published under the Sun SLA.
For more details please follow Terrence Barr.

Q: How does LWUIT compare to FX?

Terrence Barr answered this in great detail.

Technical Issues

Q: I'm experiencing a performance problem with LWUIT, what should I do?

See if the performance problem exists in the LWUIT Demo, LWUIT-Makeover etc. If the use case isn't represented there try to build a use case which represents the performance issue and investigate.
Both the developer guide and the blog cover the issue of optimizing performance and memory footprint.

Q: I'm getting out of memory errors in LWUIT/LWUIT is consuming allot of memory in my memory monitor

Check that your application doesn't hold onto pointers for components, since a component references its parent component holding onto a single button can keep an entire form with all its content in memory... LWUIT allocates and discards frequently to allow for a small memory footprint, this causes the graph of free memory to fluctuate but the alternative of caching would be worse for highly constrained devices. Check out the LWUIT blog for more information on the subject of tracking and identifying memory issues.

Q: Why my list/text area won't scroll/jumps around?

You need to disable the scrolling for the form using myForm.setScrollable(false) and you should place the list in a center of a border layout. For deeper understanding of why this is required read the next question about scrolling.

Q: How can I make scrolling more elaborate? Does LWUIT only support scrolling based on focus? Why isn't scrolling of an element larger than screen size supported?

LWUIT features an open interface for scrolling allowing any component to define the way in which it wishes to scroll. This interface is used by the TextArea and List components to implement their internal scroll functionality.
LWUIT doesn't scroll containers, instead it provides focus traversal which causes scrolling to the focused component. This is a very powerful approach (and very common on small devices) since it allows easy interaction, however in some circumstances (mostly viewers) LWUIT focus based scrolling doesn't behave as expected. Since the scrolling architecutre is exposed, developers can extend container and override the scrolling/key handling to behave as expected.
Scrolling a single component which is larger than the screen isn't supported by LWUIT containers by default (this is a very difficult edge case for focus based scrolling). Scrolling multiple smaller components is not a problem.
Community member Elliot Long contributed his own solution to "visual scrolling" which allows scrolling without focus. The LWUIT blog covers simple image scrolling and explains the details here.

Q: How do I change the appearance of the list? Remove the numbers from the side etc? Can I nest containers in the list?

List is designed for a very large number of element and fast traversal, you can use its cell renderer facility to customize it any way you want as explained here. How the list can scale and grow is explained here and additionally here.

Q: My application freeses or stalls how do I fix this?

99% of the problems of this type are related to EDT violations. The EDT is the Event Dispatch Thread which broadcasts all the events in LWUIT, it is also responsible for drawing all elements on the screen.
The EDT thread is responsible for drawing all screen elements, if it is blocked by a long running operation elements won't update and key/pointer events won't be received. The solution is to use threads for such long running tasks, however interaction with LWUIT can only be performed on the EDT. To return into the EDT you can use Display.callSerially/callSeriallyAndWait, a different option is to use invokeAndBlock.

Q: I'm not opening any threads but getting some problems?

A typical application always uses at least two threads, lifecycle and the EDT. The lifecycle thread is the callback thread used for the application, e.g. in MIDP the startApp method is invoked from the MIDP thread which is different from the EDT.

Q: Can nothing work from a separate thread?

There are no guarantees, repaint() should generally work from every thread and show() should as well.

Q: How do I reposition/resize a dialog?

Use a Dialog instance and a version of show which accepts 4 integer values to position the dialog. You can use the set the default dialog position to simplify dialog positioning.

Q: How do I show Video?

Use MMAPI to create a Player object which you can submit to the MediaComponent class.

Q: How do I show SVG/3D?

Use the M3G API or the SVGImage API to place such elements in the UI.

Q: Can I create my own components?

Everything in LWUIT is fully extensible, you can derive from any component and extend it. It is demonstrated in the developer guide and extensively in the blog.

Q: I'm trying to display an animated gif and thats not working?

Animated gifs can be shown in MIDP using the MMAPI and MediaComponent (see the MMAPI question). LWUIT has special support for StaticAnimation which is a LWUIT specific format very similar to the animated gif. Both the resource editor and the ant task accept animated GIF files to create static animations.

Q: I'm having problems on the BlackBerry?

The BlackBerry VM has some issues with linking to classes that aren't on the device, a BlackBerry specific version built with the BlackBerry VM is necessary. See the LWUIT-incubator project for a community built port for the BlackBerry.

Q: I'm having issues on a Windows Mobile device?

Windows mobile VM's vary significantly in their quality if the VM is giving you problems try the Phone ME open source VM port for Windows mobile devices.


Q: How do I create resource (.res) files?

Use the LWUIT Designer (formerly the resource editor) or Ant task, both are covered in the developer guide.

Q: What is the difference between the LWUIT Designer (Resource Editor) and the Ant task?

The difference is mainly in the use case, the ant tool is designed mostly for developer related resources (locales, application images etc..). The LWUIT Designer is desgined for use by graphics desginers.

Q: Can I Export Resource Files to Ant XML?

No, allot of the information no longer exists within the resource file such as the actual name of the bitmap fonts etc.
However, we are considering a future modification to the resource file format that will allow such functionality.

Q: What is compatibility mode?

Compatibility mode allows LWUIT styles to function in a way similar to the first revisions of LWUIT where one style mapped to one component instance. Newer versions of LWUIT allow 2 or more styles per component and deprecate the usage of the selection attributes (bgSelectionColor, fgSelectionColor) in favor of a separate style to indicate selection state.
Existing code that manipulates styles using the getStyle()/setStyle() methods might not function in the same way. For further details please read:

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