Cache mapped values and objects

app/src/main/java/org/solovyev/android/prefs/CachingMapper.java

@@ -0,0 +1,63 @@
+package org.solovyev.android.prefs;
+
+import android.support.annotation.NonNull;
+import android.text.TextUtils;
+
+import org.solovyev.common.text.Mapper;
+
+import java.util.Objects;
+
+import javax.annotation.Nullable;
+
+public final class CachingMapper<T> implements Mapper<T> {
+
+    private static class CachedEntry<T> {
+        @Nullable
+        private String value;
+        @Nullable
+        private T object;
+    }
+
+    @NonNull
+    private final Mapper<T> mapper;
+    @Nullable
+    private CachedEntry<T> cachedEntry = null;
+
+    private CachingMapper(@NonNull Mapper<T> mapper) {
+        this.mapper = mapper;
+    }
+
+    @NonNull
+    public static <T> Mapper<T> of(@NonNull Mapper<T> mapper) {
+        if (mapper.getClass().equals(CachingMapper.class)) {
+            return mapper;
+        }
+        return new CachingMapper<>(mapper);
+    }
+
+    @Nullable
+    @Override
+    public synchronized T parseValue(@Nullable String value) throws IllegalArgumentException {
+        if (cachedEntry == null) {
+            cachedEntry = new CachedEntry<>();
+        } else if (TextUtils.equals(cachedEntry.value, value)) {
+            return cachedEntry.object;
+        }
+        cachedEntry.value = value;
+        cachedEntry.object = mapper.parseValue(value);
+        return cachedEntry.object;
+    }
+
+    @Nullable
+    @Override
+    public synchronized String formatValue(@Nullable T object) throws IllegalArgumentException {
+        if (cachedEntry == null) {
+            cachedEntry = new CachedEntry<>();
+        } else if (Objects.equals(cachedEntry.object, object)) {
+            return cachedEntry.value;
+        }
+        cachedEntry.object = object;
+        cachedEntry.value = mapper.formatValue(object);
+        return cachedEntry.value;
+    }
+}

app/src/main/java/org/solovyev/android/prefs/StringPreference.java

@@ -43,7 +43,7 @@ public final class StringPreference<T> extends AbstractPreference<T> {
 
     public StringPreference(@Nonnull String key, @Nullable T defaultValue, @Nonnull Mapper<T> mapper) {
         super(key, defaultValue);
-        this.mapper = mapper;
+        this.mapper = CachingMapper.of(mapper);
     }
 
     @Nonnull

app/src/main/java/org/solovyev/common/text/EnumMapper.java

@@ -22,11 +22,12 @@
 
 package org.solovyev.common.text;
 
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.Map;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 public class EnumMapper<T extends Enum> implements Mapper<T> {
 
     @Nonnull

app/src/main/java/org/solovyev/common/text/NumberMapper.java

@@ -23,13 +23,15 @@
 package org.solovyev.common.text;
 
 import org.solovyev.android.Check;
+import org.solovyev.android.prefs.CachingMapper;
 
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 public class NumberMapper<N extends Number> implements Mapper<N> {
 
     private static final List<Class<? extends Number>> supportedClasses = NumberParser.supportedClasses;
@@ -38,7 +40,7 @@ public class NumberMapper<N extends Number> implements Mapper<N> {
 
     static {
         for (Class<? extends Number> supportedClass : supportedClasses) {
-            mappers.put(supportedClass, newInstance(supportedClass));
+            mappers.put(supportedClass, CachingMapper.of(newInstance(supportedClass)));
         }
     }