Version 5.6
Copyright © 2009, 2010 , 2011, 2012 Lars Vogel
03.11.2011
| Revision History | |||
|---|---|---|---|
| Revision 0.1 | 14.02.2009 | Lars Vogel |
created |
| Revision 0.2 - 5.6 | 16.02.2009 - 03.11.2011 | Lars Vogel |
bug fixes and enhancements |
Table of Contents
Preferences are key / value pairs, where the key is an arbitrary name for the preference. The value can be a boolean, string, int or another primitive type. For example a user name might be stored via a key called user . The actual value for this key might be "Lars Vogel".
Eclipse
Preferences
are based on the
Preferences
class from the
org.osgi.service.prefs
package. Eclipse
Preferences
are
very
similar to standard Java
Preferences
with some support of
additional features. They use the
Eclipse
framework
to save and
retrieve
the configuration.
The Eclipse runtime defines three so-called scopes. The scope defines how the preference data is stored and how it is changeable.
Table 1. Eclipse Preference scope
| Scope | Description |
|---|---|
| Instance scope | If the user runs the same program twice, the settings between the two programs may be different. |
| Configuration scope | If the user runs the same program twice then the settings between the two programs are the same. |
| Default scope | Default values which can not be changed. Supplied via configuration files in plug-ins and product definitions. |
You can create and manipulate preferences directly in
your coding.
Preferences are read and saved by
get()
and
put()
methods. In the
get()
method you specify a default value in case the key can not be
found.
The
clear()
method
allows to delete a preference value.
// We access the Configuration Scope Preferences preferences = ConfigurationScope.INSTANCE .getNode("de.vogella.preferences.test"); Preferences sub1 = preferences.node("node1"); Preferences sub2 = preferences.node("node2"); sub1.put("h1", "Hello"); sub1.put("h2", "Hello again"); sub2.put("h1", "Moin"); try { // Forces the application to save the preferences preferences.flush(); } catch (BackingStoreException e) { e.printStackTrace(); } }
// Read values from the configuration scope Preferences preferences = ConfigurationScope.INSTANCE .getNode("de.vogella.preferences.test"); Preferences sub1 = preferences.node("node1"); Preferences sub2 = preferences.node("node2"); sub1.get("h1", "default"); sub1.get("h2", "default"); sub2.get("h1", "default");
You
can use a file to set certain preference
values. This files needs
to get registered via the
preferenceCustomization
property on your product extension point. This file is
typically named
plugin_customization.ini.
The format to use is <plugin id>/<setting>=<value>, e.g. de.vogella.test.preference/check=true.
To find the right values, just start your Eclipse application,
switch
to the
.metadata
directory in your workspace directory (by
default the directory your
application is starting in) and search for
files ending with
.pref.
Eclipse 4 provides dependency injection to simplify the handling of preferences. It allows you to access Preferences via dependency injection.
// Get IEclipsePreferences to change a value @Execute public void execute (@Preference(nodePath = "com.example.e4.rcp.todo") IEclipsePreferences prefs) { // More stuff... prefs.put("user", "TestUser"); prefs.put("password", "Password"); // Persists try { prefs.flush(); } catch (BackingStoreException e) { e.printStackTrace(); } }
Eclipse allows to track the values of preference settings. If these
values change Eclipse will re-inject the values.
Eclipse can
track
changes
in the
InstanceScope
and
ConfigurationScope.
Preferences
in the
DefaultScope
will not be tracked.
@Inject @Optional public void trackUserSettings (@Preference(nodePath = "com.example.e4.rcp.todo", value = "user") String user) { System.out.println("New user: " + user); } @Inject @Optional public void trackPasswordSettings (@Preference(nodePath = "com.example.e4.rcp.todo", value = "password") String password) { System.out.println("New password: " + password); }
Before posting questions, please see the vogella FAQ. If you have questions or find an error in this article please use the www.vogella.com Google Group. I have created a short list how to create good questions which might also help you.
http://wiki.eclipse.org/E4 Eclipse E4 - Wiki
