Converting an AWT application to SWT/JFace

Question

I am currently toying with the idea of converting a small/medium sized project from AWT to SWT, although Swing is not totally out of the picture yet. I was thinking about converting the main window to an SWT_AWT bridge object, but I have no idea how the semantics for this work. After that, I plan to update dialog for dialog, but not necessarily within one release. Is this possible?

Has someone done a conversion like this and can give me some hints? Is there maybe even a tutorial somewhere out there? Is there maybe even a tool that can automate parts of this? I have tried googling, but to no avail.

Update: One additional thing is: Currently, this is a netbeans project. Might be of help or not, I don't know.

Answer 1

We have done this quite a few times. But only because we are going from a Swing application to an Eclipse RCP application not because we like messing with things. This project will really let you know whether you've separated your controller/model code from your view code.

One suggestion is to not try and convert everything all at once. You will end up with a bunch of mixed code that doesn't work at all. You can start at converting portals. I would consider a portal anything within a Tab, Dialog, or Window, essentially self contained unit. If you have a window that opens up, create the Window in SWT, but make it's contents the existing AWT/Swing. This should be fairly straight forward and allow you to get used to the (I really hope they weren't drunk and had a good reason for this) way of instantiating and associating parent/child controls.

One gotcha that can occur is with transparent components. Swing, with the exception of a "window" class is all rendered in Java. This makes it very easy to render things the way you want them. In SWT, there are some restrictions:

• Borders. If you use SWT.BORDER you are stuck with whatever color the native component uses. Your best bet is to use a PaintListener and render your own borders if you want them in a different style or color.
• Transparent labels, progress bars. I have not been able to get Labels or Progress Bars to have a transparent background. If you want them to take on the parent color, or drawing you will need to render the text and other controls yourself.
• Controls. There are composites and controls in SWT. Think of Controls as the basic native controls that do all the native API calls. These cannot be subclassed, which makes things difficult.
• Tables will give you the most trouble. Make sure everything is stable before you attempt to convert a JTable to a Table or TableViewer. You will spend some time on these, especially if you have custom editors and viewers.

I have not researched why SWT was designed the way it was. I am guessing there HAD to be a good reason. It would be great if someone had a blog or defense to it's design so I don't have to search for it. Once it's posted I'll remove these lines since they have no relevance to the question.

Addition

I want to add that since you have an existing product I assume works. The best piece of advice I can give you is to never let your code get into a state that it cannot compile and run. If you work on your conversion and whatever you check in always runs and executes (despite the visual differences between SWT/AWT/Swing) you will save yourself many headaches in the long run. The worst thing you can do is try to tackle this all at once and get your code in an unstable state for weeks at a time.

Answer 2

我建议将它导入WindowBuilder项目，因为WindowBuilder使您能够解析现有代码并创建GUI模型，然后将组件转换为SWT或Swing。

Answer 3

如果您考虑在同一个应用程序中混合使用SWT和Swing，那么这个Eclipse Corner文章将非常有用。

Answer 4

We are preparing the same step: Swing to SWT/JFace. First we try to determine the bottlenecks: reimplement special components derived from JComponent with SWT/JFace, search for a replacement of JIDE docking (we want to use SWT/JFace, not RCP to avoid too much hassle). The worst thing we already imagine is, that in Swing you could create components and adding it later to the parent. With SWT this is not possible: the parent component must be passed as a reference to the child component's constructor. This will require major refactoring in the Swing application before using SWT.

Frankly, we rate the conversion a very heavy change, because we expect the time where nothing can be compiled as quite long. We try to decrease this time by preparing everything as good as possible, but we'll see how good it will work.

Update from April 6th 2011:

We now refactored our Swing application to always create components with their parent (as in SWT). Our subclasses of JFrame and JDialog got refactored to just have a JDialog instance to make it easier to switch to SWT's Shell . In parallel, we rewrite sophisticated components in SWT.