Bug 75988 [Preferences] IPreferencePage#performOk() returning false should prevent the dialog from closing
I think that if this method returns false, it should prevent the dialog from closing. Today, in order to perform validation I have to register key listeners to all fields an use #setValid(false) to disable the "OK" button.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
setLastTreeWidth(newWidthHint);
				composite.layout(true);
				
				computedSize = getShell().computeSize(SWT.DEFAULT, SWT.DEFAULT);
				
				
				if (customSize)
					computedSize.x = Math.max(computedSize.x, currentSize.x);
				computedSize.y = Math.max(computedSize.y, currentSize.y);
				if (computedSize.equals(currentSize))
					return;
				setShellSize(computedSize.x, computedSize.y);
				lastShellSize = getShell().getSize();
			}
		});
		return sash;
	}
	/**
	 * Creates the inner page container.
	 * 
	 * @param parent
	 * @return Composite
	 */
	protected Composite createPageContainer(Composite parent) {
		Composite result = new Composite(parent, SWT.NULL);
		result.setLayout(getPageLayout());
		return result;
	}
	/**
	 * Return the layout for the composite that contains