Eclipse 4 Preferences

Eclipse 4 Preferences - Tutorial

Based on Eclipse 4.2

Lars Vogel

Version 5.6

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

Using Eclipse 4 Preferences

This tutorial gives an overview how preference values can be used in Eclipse 4.

Table of Contents

1. Eclipse Preferences

1.1. Preferences and Scopes
1.2. Eclipse direct Preference API
1.3. plugin_customization.ini

2. Eclipse 4 Preferences

3. Thank you

4. Questions and Discussion

5. Links and Literature

5.1. Source Code

1. Eclipse Preferences

1.1. Preferences and Scopes

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 org.osgi.service.prefs.Preferences class. 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 plugins and product definitions.

1.2. Eclipse direct Preference API

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 also 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("note1");
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("note1");
Preferences sub2 = preferences.node("node2");
sub1.get("h1", "default");
sub1.get("h2", "default");
sub2.get("h1", "default");

1.3. plugin_customization.ini

You can use the file plugin_customization.ini to set preference values. For format to use is <plugin id> / <setting> = <value></para>.e.g. de.vogella.test.proference/check=true.

To find the right values, just start your Eclipse application, switch to the .metadata directory in your workspace directory (per default the directory your application is starting in) and search for files ending with "".pref".

2. Eclipse 4 Preferences

Eclipse 4 provides dependency injection to simplify the handling of preferences. It allows to access Preferences via dependency injection and to track changes.

Eclipse will track changes for Preferences in the InstanceScope and ConfigurationScope. Preferences in the DefaultScope will not be tracked.

			
// Instance Scope is tracked
Preferences node = new InstanceScope().getNode("de.vogella.e4.todo");
node.put("key", "2012");
   
// Injection will be called
@Inject
@Preference(value = "key", nodePath = "de.vogella.e4.todo")
String year;

//
@Inject
public TestView() {
    Preferences node = new DefaultScope().getNode("test.project");       
	node.put("key", "2010");
}

// Setting the preference via DI
@Inject
    public void createControl(final Composite composite, @Preference final
IEclipsePreferences node) {
		Button store = new Button(composite, SWT.PUSH);
        store.addSelectionListener(new SelectionAdapter() {
            @Override
            public void widgetSelected(SelectionEvent e) {
                node.put("key", "myValue");
            }
        });

    }

3. Thank you

Please help me to support this article:

4. Questions and Discussion

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.

5. Links and Literature

5.1. Source Code

Source Code of Examples

http://wiki.eclipse.org/E4 Eclipse E4 - Wiki

Eclipse RCP

Eclipse EMF

Dependency Injection