String relativePath = getFilesDir().getAbsolutePath() + "/mmkv_3";
MMKV kv = MMKV.mmkvWithID("testCustomDir", relativePath);

SharedPreferences 迁移

1、MMKV 提供了 importFromSharedPreferences() 函数，可以比较方便地迁移数据过来。

2、MMKV 还额外实现了一遍 SharedPreferences、SharedPreferences.Editor 这两个 interface，在 迁移的时候只需两三行代码即可，其他 CRUD 操作代码都不用改。

    //SharedPreferences preferences = getSharedPreferences("myData", MODE_PRIVATE);MMKV preferences = MMKV.mmkvWithID("myData");// 迁移旧数据{SharedPreferences old_man = getSharedPreferences("myData", MODE_PRIVATE);preferences.importFromSharedPreferences(old_man);old_man.edit().clear().commit();}// 跟以前用法一样SharedPreferences.Editor editor = preferences.edit();editor.putBoolean("bool",true);editor.putInt("int",Integer.MIN_VALUE);editor.putLong("long",Long.MAX_VALUE);editor.putFloat("float",-3.14f);editor.putString("string","hello, imported");HashSet<String> set = new HashSet<String>();set.add("W");set.add("e");set.add("C");set.add("h");set.add("a");set.add("t");editor.putStringSet("string-set",set);// 无需调用 commit()// editor.commit();

工具类封装如下：

public class SpUtils {private static SpUtils mInstance;private static MMKV mv;private SpUtils2() {mv = MMKV.defaultMMKV();}/*** 初始化MMKV,只需要初始化一次，建议在Application中初始化 **/public static SpUtils getInstance() {if (mInstance == null) {synchronized (SpUtils.class) {if (mInstance == null) {mInstance = new SpUtils();}}}return mInstance;}/*** 保存数据的方法，我们需要拿到保存数据的具体类型，然后根据类型调用不同的保存方法 */public static void encode(String key, Object object) {if (object instanceof String) {mv.encode(key, (String) object);} else if (object instanceof Integer) {mv.encode(key, (Integer) object);} else if (object instanceof Boolean) {mv.encode(key, (Boolean) object);} else if (object instanceof Float) {mv.encode(key, (Float) object);} else if (object instanceof Long) {mv.encode(key, (Long) object);} else if (object instanceof Double) {mv.encode(key, (Double) object);} else if (object instanceof byte[]) {mv.encode(key, (byte[]) object);} else {mv.encode(key, object.toString());}}public static void encodeSet(String key, Set<String> sets) {mv.encode(key, sets);}public static void encodeParcelable(String key, Parcelable obj) {mv.encode(key, obj);}/**得到保存数据的方法，我们根据默认值得到保存的数据的具体类型，然后调用相对于的方法获取值*/public static Integer decodeInt(String key) {return mv.decodeInt(key, 0);}public static Double decodeDouble(String key) {return mv.decodeDouble(key, 0.00);}public static Long decodeLong(String key) {return mv.decodeLong(key, 0L);}public static Boolean decodeBoolean(String key) {return mv.decodeBool(key, false);}public static Float decodeFloat(String key) {return mv.decodeFloat(key, 0F);}public static byte[] decodeBytes(String key) {return mv.decodeBytes(key);}public static String decodeString(String key) {return mv.decodeString(key, "");}public static Set<String> decodeStringSet(String key) {return mv.decodeStringSet(key, Collections.<String>emptySet());}public static Parcelable decodeParcelable(String key) {return mv.decodeParcelable(key, null);}/*** 移除某个key对 ** @param key */public static void removeKey(String key) {mv.removeValueForKey(key);}/*** 清除所有key */public static void clearAll() {mv.clearAll();}
}

参考：MMKV 原理以及使用 - 简书