Returns the summary of this SummaryPreference.
Returns the summary of this SummaryPreference. If the summary has a String formatting marker in it (i.e. "%s" or "%1$s"), then the current entry value will be substituted in its place.
the summary with appropriate string substitution
Make your preference support %s in summary. Override getSummaryValue to customize what to put in. Based on: https://github.com/android/platform_frameworks_base/blob/master/core/java/android/preference/ListPreference.java