android_tutorial

MMKV for Android

MMKV is an efficient, small, easy-to-use mobile key-value storage framework used in the WeChat application. It's currently available on both Android, iOS/macOS, Windows and POSIX.

Tutorial

You can use MMKV as you go. All changes are saved immediately, no sync, no apply calls needed.

Configuration

• Setup MMKV on App startup, say your Application class, add these code:

  public void onCreate() {
      super.onCreate();
  
      String rootDir = MMKV.initialize(this);
      System.out.println("mmkv root: " + rootDir);
  }

CRUD Operations

• MMKV has a global instance, you can use it directly:

  import com.tencent.mmkv.MMKV;
  ...
  MMKV kv = MMKV.defaultMMKV();
  
  kv.encode("bool", true);
  System.out.println("bool: " + kv.decodeBool("bool"));
  
  kv.encode("int", Integer.MIN_VALUE);
  System.out.println("int: " + kv.decodeInt("int"));
  
  kv.encode("long", Long.MAX_VALUE);
  System.out.println("long: " + kv.decodeLong("long"));
  
  kv.encode("float", -3.14f);
  System.out.println("float: " + kv.decodeFloat("float"));
  
  kv.encode("double", Double.MIN_VALUE);
  System.out.println("double: " + kv.decodeDouble("double"));
  
  kv.encode("string", "Hello from mmkv");
  System.out.println("string: " + kv.decodeString("string"));
  
  byte[] bytes = {'m', 'm', 'k', 'v'};
  kv.encode("bytes", bytes);
  System.out.println("bytes: " + new String(kv.decodeBytes("bytes")));

  As you can see, MMKV is quite easy to use.

• Deleting & Querying:

  MMKV kv = MMKV.defaultMMKV();
  
  kv.removeValueForKey("bool");
  System.out.println("bool: " + kv.decodeBool("bool"));
      
  kv.removeValuesForKeys(new String[]{"int", "long"});
  System.out.println("allKeys: " + Arrays.toString(kv.allKeys()));
  
  boolean hasBool = kv.containsKey("bool");

• If different modules/logics need isolated storage, you can also create your own MMKV instance separately:

  MMKV kv = MMKV.mmkvWithID("MyID");
  kv.encode("bool", true);

• If multi-process accessing is needed, you can set MMKV.MULTI_PROCESS_MODE on MMKV initialization:

  MMKV kv = MMKV.mmkvWithID("InterProcessKV", MMKV.MULTI_PROCESS_MODE);
  kv.encode("bool", true);

Supported Types

• Primitive Types:

  • boolean, int, long, float, double, byte[]

• Classes & Collections:

  • String, Set<String>
  • Any class that implements Parcelable

Migrating from SharedPreferences

• MMKV provides importFromSharedPreferences(), you can migrate from SharedPreferences with one line of code;

• MMKV implements SharedPreferences & SharedPreferences.Editor. You can just change initialization & declaration to MMKV, and leave those CRUD codes untouched.

  private void testImportSharedPreferences() {
      //SharedPreferences preferences = getSharedPreferences("myData", MODE_PRIVATE);
      MMKV preferences = MMKV.mmkvWithID("myData");
      // migration
      {
          SharedPreferences old_man = getSharedPreferences("myData", MODE_PRIVATE);
          preferences.importFromSharedPreferences(old_man);
          old_man.edit().clear().commit();
      }
      // just use it as before
      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);
      // commit() is not needed any more
      //editor.commit();
  }

What's Next

• Android in Advance
• Android Performence