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
return textValue;
		}
		int length = textValue.length();
		int ellipsisWidth = gc.textExtent(ellipsis).x;
		int pivot = length / 2;
		int start = pivot;
		int end = pivot + 1;
		while (start >= 0 && end < length) {
			String s1 = textValue.substring(0, start);
			String s2 = textValue.substring(end, length);
			int l1 = gc.textExtent(s1).x;
			int l2 = gc.textExtent(s2).x;
			if (l1 + ellipsisWidth + l2 < maxWidth) {
				gc.dispose();
				return s1 + ellipsis + s2;
			}
			start--;
			end++;
		}
		gc.dispose();
		return textValue;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.jface.preference.IPreferencePageContainer#updateTitle()
	 */
	public void updateTitle() {
		if(currentPage == null)
			return;