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什么是MMKV
MMKV的github地址:https://github.com/Tencent/MMKV
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简介
MMKV is an efficient, small, easy-to-use mobile key-value storage framework used in the WeChat application. It's currently available on Android, iOS/macOS, Win32 and POSIX.
官方介绍说MMKV是一套更有效率、更小、更易使用的移动端键值对存储框架,目前应用于微信App中,并且可以作为第三方框架用于Android、ios、win32和posix(Portable Operating System Interface可移植操作系统接口)系统。
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特点
- Efficient. MMKV uses mmap to keep memory synced with file, and protobuf to encode/decode values, making the most of Android to achieve best performance.
- Multi-Process concurrency: MMKV supports concurrent read-read and read-write access between processes.
- Easy-to-use. You can use MMKV as you go. All changes are saved immediately, no
sync
, noapply
calls needed. - Small.
- A handful of files: MMKV contains process locks, encode/decode helpers and mmap logics and nothing more. It's really tidy.
- About 50K in binary size: MMKV adds about 50K per architecture on App size, and much less when zipped (apk).
因为使用的是mmap(一种内存映射文件方法)去保持内存和文件数据同步,并且使用protobuf编解码value,所以相较于Android传统的基于xml的SharedPreferences来说更有效率,并且支持多进程并发读写,这也相当于提高了效率。
相比于SP,所有的改变通过encode方法立即存入,不需要像SP调用apply存入内存,也不需要调用commit存入文件。
MMKV只包括进程锁、编解码的helper和mmap的逻辑,再没有其他的文件,在每个App中大约占50K,编译成apk的时候还会进一步压缩。
- Efficient. MMKV uses mmap to keep memory synced with file, and protobuf to encode/decode values, making the most of Android to achieve best performance.
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支持的类型
- 基本类型:boolean, int, long, float, double, byte[]
- Classes & Collections:
- String,Set
- Any class that implements
Parcelable
实现了Parcelable的自定义bean
- String,Set
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使用
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添加依赖
首先,作为第三方库的引入,当然是添加依赖:
dependencies { implementation 'com.tencent:mmkv-static:1.2.5' // replace "1.2.5" with any available version }
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初始化
初始化通常只在App启动的时候执行一次,所以放在继承自Application的自定义类下:
class MyApp extends Application{ public void onCreate() { super.onCreate(); String rootDir = MMKV.initialize(this); System.out.println("mmkv root: " + rootDir); //…… } }
注意这里的initialize方法有很多重载方法可以用:
public static String initialize(Context context) { String root = context.getFilesDir().getAbsolutePath() + "/mmkv"; MMKVLogLevel logLevel = MMKVLogLevel.LevelInfo; return initialize(root, (MMKV.LibLoader)null, logLevel); } public static String initialize(Context context, MMKVLogLevel logLevel) { String root = context.getFilesDir().getAbsolutePath() + "/mmkv"; return initialize(root, (MMKV.LibLoader)null, logLevel); } public static String initialize(String rootDir) { MMKVLogLevel logLevel = MMKVLogLevel.LevelInfo; return initialize(rootDir, (MMKV.LibLoader)null, logLevel); } public static String initialize(String rootDir, MMKVLogLevel logLevel) { return initialize(rootDir, (MMKV.LibLoader)null, logLevel); } public static String initialize(String rootDir, MMKV.LibLoader loader) { MMKVLogLevel logLevel = MMKVLogLevel.LevelInfo; return initialize(rootDir, loader, logLevel); } public static String initialize(String rootDir, MMKV.LibLoader loader, MMKVLogLevel logLevel) { if (loader != null) { if ("StaticCpp".equals("SharedCpp")) { loader.loadLibrary("c++_shared"); } loader.loadLibrary("mmkv"); } else { if ("StaticCpp".equals("SharedCpp")) { System.loadLibrary("c++_shared"); } System.loadLibrary("mmkv"); } jniInitialize(rootDir, logLevel2Int(logLevel)); MMKV.rootDir = rootDir; return MMKV.rootDir; }
最后都会回调到initialize(String rootDir, MMKV.LibLoader loader, MMKVLogLevel logLevel)这个方法。
第一个参数是MMKV保存数据文件的路径,默认路径是context.getFilesDir().getAbsolutePath() + "/mmkv",你可以指定其他的合法路径作为存放地址;
通过第二个参数可以自定义MMKV库加载器:
public interface LibLoader { void loadLibrary(String var1); }
通常我们不需要自定义,默认使用System的loadLibrary方法去加载MMKV类库。
第三个参数是设置MMKV输出Log的等级,默认info等级,无须多言。
经过类库加载,MMKV就被加载到了JVM中,jniInitialize方法是native方法,底层调用MMKV的c++方法进行初始化逻辑。
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存放、读取
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")));
encode方法是存储,第一个参数是key,第二个参数是value;
decodeXxx方法是读取,decode后面跟着要读取的value类型,参数是key。
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移除、查询
MMKV kv = MMKV.defaultMMKV(); kv.removeValueForKey("bool"); System.out.println("bool: " + kv.decodeBool("bool")); //批量删除 kv.removeValuesForKeys(new String[]{"int", "long"}); System.out.println("allKeys: " + Arrays.toString(kv.allKeys())); //查看是否保存过某个key-value对 boolean hasBool = kv.containsKey("bool");
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模块化
If different modules/logics need isolated storage, you can also create your own MMKV instance separately.
对于不同功能模块还可以创建针对性的mmkv对象:
MMKV mmkv = MMKV.mmkvWithID("MyID"); mmkv.encode("bool", true);
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模式
MMKV mmkv = MMKV.mmkvWithID("InterProcessKV", MMKV.MULTI_PROCESS_MODE); mmkv.encode("bool", true);
包括defaultMMKV方法,都可以设置是多线程模式还是单线程模式,默认是单线程模式。
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导入SP
MMKV实现了SharedPreferences和SharedPreferences.Editor,所以你可以使用SP的api调用,比如:
public Editor putString(String key, @Nullable String value) { this.encodeString(this.nativeHandle, key, value); return this; }
可见不需要commit和apply,当然你可以在后面加上commit或apply,但实际上没有任何意义,因为在put方法里已经调用了encodeXxx方法,之所以保留这些api是为了适配SP使用者的习惯。
MMKV里定义了导入SP的方法importFromSharedPreferences(SharedPreferences preferences):
public int importFromSharedPreferences(SharedPreferences preferences) { Map
kvs = preferences.getAll(); if (kvs != null && kvs.size() > 0) { Iterator var3 = kvs.entrySet().iterator(); while(var3.hasNext()) { Entry entry = (Entry)var3.next(); String key = (String)entry.getKey(); Object value = entry.getValue(); if (key != null && value != null) { if (value instanceof Boolean) { this.encodeBool(this.nativeHandle, key, (Boolean)value); } else if (value instanceof Integer) { this.encodeInt(this.nativeHandle, key, (Integer)value); } else if (value instanceof Long) { this.encodeLong(this.nativeHandle, key, (Long)value); } else if (value instanceof Float) { this.encodeFloat(this.nativeHandle, key, (Float)value); } else if (value instanceof Double) { this.encodeDouble(this.nativeHandle, key, (Double)value); } else if (value instanceof String) { this.encodeString(this.nativeHandle, key, (String)value); } else if (value instanceof Set) { this.encode(key, (Set)value); } else { simpleLog(MMKVLogLevel.LevelError, "unknown type: " + value.getClass()); } } } return kvs.size(); } else { return 0; } } 所以如果项目中之前有过SP的存储,那么只需要调用一下这个方法就会把原先SP中的数据全部设置到MMKV中。
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工具类封装
实际开发中,我们不需要每次都要从MMKV.defaultMMKV()这样开始,所以把MMKV的调用封装起来是一件重要的事情。
public class MySpUtils { private static MMKV mv = MMKV.defaultMMKV();; private MySpUtils() {} /** * 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
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 decodeStringSet(String key) { return mv.decodeStringSet(key, Collections. emptySet()); } public static Parcelable decodeParcelable(String key) { return mv.decodeParcelable(key, null); } /** * 移除某个key对 */ public static void removeKey(String key) { mv.removeValueForKey(key); } /** * 移除部分key */ public static void removeSomeKey(String[] keyArray) { mv.removeValuesForKeys(keyArray); } /** * 清除所有key */ public static void clearAll() { mv.clearAll(); } /** * 判断是否含有某个key */ public static void hasKey(String key){ return mv.containsKey(key); } } 也可以根据需要添加各种定制化方法来设置线程模式、mmapId等。