iOS_tutorial

MMKV for iOS/macOS

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 synchronize calls are needed.

Configuration

• Setup MMKV on App startup, in your -[MyApp application: didFinishLaunchingWithOptions:], add these lines:

  - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
      // init MMKV in the main thread
      [MMKV initializeMMKV:nil];
  
      //...
      return YES;
  }

• If multi-process accessing is needed(between the App and extensions), you need to set the group directory on MMKV initialization:

  NSString *myGroupID = @"group.company.mmkv";
  // the group dir that can be accessed by App & extensions
  NSString *groupDir = [[NSFileManager defaultManager] containerURLForSecurityApplicationGroupIdentifier:myGroupID].path;
  [MMKV initializeMMKV:nil groupDir:groupDir logLevel:MMKVLogInfo];

  Notice: When using MMKV in AppExtension or WatchExtension, you should link MMKV to your target by dynamic linking(for details, check the setup again).

CRUD Operations

• MMKV has a default instance, which could be used directly:

  MMKV *mmkv = [MMKV defaultMMKV];
  
  [mmkv setBool:YES forKey:@"bool"];
  NSLog(@"bool:%d", [mmkv getBoolForKey:@"bool"]);
  
  [mmkv setInt32:-1024 forKey:@"int32"];
  NSLog(@"int32:%d", [mmkv getInt32ForKey:@"int32"]);
  
  [mmkv setInt64:std::numeric_limits<int64_t>::min() forKey:@"int64"];
  NSLog(@"int64:%lld", [mmkv getInt64ForKey:@"int64"]);
  
  [mmkv setFloat:-3.1415926 forKey:@"float"];
  NSLog(@"float:%f", [mmkv getFloatForKey:@"float"]);
  
  [mmkv setString:@"hello, mmkv" forKey:@"string"];
  NSLog(@"string:%@", [mmkv getStringForKey:@"string"]);
  
  [mmkv setDateorKey:@"date"];
  NSLog(@"date:%@", [mmkv getDateForKey:@"date"]);
  
  NSData *data = [@"hello, mmkv again and again" dataUsingEncoding:NSUTF8StringEncoding];
  [mmkv setDataForKey:@"data"];
  data = [mmkv getDataForKey:@"data"];

NSLog(@"data:%@", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);

NSDictionary *dic = @{@"key1" : @"value1",
                      @"key2" : @(2)};
[mmkv setObject:dic forKey:@"dictionary"];
dic = [mmkv getObjectOfClass:[NSDictionary class] forKey:@"dictionary"];
NSLog(@"dictionary:%@", dic);

```

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

• Deleting, Querying & Enumerating:

  MMKV *mmkv = [MMKV defaultMMKV];
  
  [mmkv removeValueForKey:@"bool"];
  [mmkv removeValuesForKeys:@[@"int32", @"int64"]];
  
  BOOL hasBool = [mmkv containsKey:@"bool"];
      
  [mmkv enumerateKeys:^(NSString *key, BOOL *stop) {
      if ([key isEqualToString:@"string"]) {
          NSString *value = [mmkv getStringForKey:key];
          NSLog(@"%@ = %@", key, value);
          *stop = YES;
      }
  }];
  
  // delete everything
  [mmkv clearAll];

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

  MMKV *mmkv = [MMKV mmkvWithID:@"MyID"];
  [mmkv setBool:YES forKey:@"bool"];

• If multi-process accessing is needed(between the App and extensions), you need to set the group directory on MMKV initialization as written before. Then you can get one by passing MMKVMultiProcess:

  MMKV *mmkv = [MMKV mmkvWithID:@"MyMultiID" mode:MMKVMultiProcess];
  [mmkv setBool:YES forKey:@"bool"];

Supported Types

• C/C++ Primitive Types：
  • bool, int32, int64, uint32, uint64, float, double
• Objective-C Class：
  • NSString, NSData, NSDate
• Any Class that implements <NSCoding> protocol.

Import from NSUserDefaults

• MMKV provides -[MMKV migrateFromUserDefaultsDictionaryRepresentation:]，you can migrate from NSUserDefaults with one line of code.

  auto userDefault = [[NSUserDefaults alloc] initWithSuiteName:@"myDefault"];
  auto mmkv = [MMKV mmkvWithID:@"testImportNSUserDefaults"];
  [mmkv migrateFromUserDefaultsDictionaryRepresentation: userDefault.dictionaryRepresentation];
  // delete keys & values from userDefault when you're done

What's Next

• iOS in Advance
• iOS Performence