MMKV基本用法

七彩极 · 发表于 2022-11-18 17:52

MMKV是基于mmap内存映射的key-value组件，底层序列化/反序列化使用protobuf实现，性能高，稳定性强，而且Android这边还支持多进程。
不管是单线程还是多线程模型下MMVK的效率都远超sp,sqllite甚至DataStore.

基本用法:
1:在App模块的build.gradle文件里添加：
implementation 'com.tencent:mmkv:1.2.14'

2:在Application里面初始化:
public void onCreate() { super.onCreate(); String rootDir = MMKV.initialize(this); System.out.println("mmkv root: " + rootDir);}
CRUD 操作
MMKV 提供一个全面的实例，可以直接使用：
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")));
可以看到，MMKV在使用上还是比较简单的。

删除 & 查询：
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");
如果不是同业需要分区存储，也可以单独创建自己的实例：
MMKV kv = MMKV.mmkvWithID("MyID");kv.encode("bool", true);
如果业务需要多进程访问，那么在刚开始化的时候加上标志位MMKV.MULTI_PROCESS_MODE：
MMKV kv = MMKV.mmkvWithID("InterProcessKV",MMKV.MULTI_PROCESS_MODE);kv.encode("bool", true);
支持的数据类型

SharedPreferences 迁移

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

MMKV还额外实现了一个遍SharedPreferences、SharedPreferences.Editor这两个界面，在迁移的时候只需要三行代码即可，其他CRUD操作代码都不能用改。

private void testImportSharedPreferences() { //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();}

高级用法
封装MMKV
创建 Preferences.kt文件

package com.vvkj.mmkvdemo.utils import android.os.Parcelable import com.tencent.mmkv.MMKV import kotlin.properties.ReadWriteProperty import kotlin.reflect.KProperty private inline fun <T> MMKV.delegate( key: String? = null, defaultValue: T, crossinline getter: MMKV.(String, T) -> T, crossinline setter: MMKV.(String, T) -> Boolean ): ReadWriteProperty<Any, T> = object : ReadWriteProperty<Any, T> { override fun getValue(thisRef: Any, property: KProperty<*>): T = getter(key ?: property.name, defaultValue) override fun setValue(thisRef: Any, property: KProperty<*>, value: T) { setter(key ?: property.name, value) }} fun MMKV.boolean( key: String? = null, defaultValue: Boolean = false ): ReadWriteProperty<Any, Boolean> = delegate(key, defaultValue, MMKV::decodeBool, MMKV::encode) fun MMKV.int(key: String? = null, defaultValue: Int = 0): ReadWriteProperty<Any, Int> = delegate(key, defaultValue, MMKV::decodeInt, MMKV::encode) fun MMKV.long(key: String? = null, defaultValue: Long = 0L): ReadWriteProperty<Any, Long> =delegate(key, defaultValue, MMKV::decodeLong, MMKV::encode) fun MMKV.float(key: String? = null, defaultValue: Float = 0.0F): ReadWriteProperty<Any, Float> =delegate(key, defaultValue, MMKV::decodeFloat, MMKV::encode) fun MMKV.double(key: String? = null, defaultValue: Double = 0.0): ReadWriteProperty<Any, Double> =delegate(key, defaultValue, MMKV::decodeDouble, MMKV::encode) private inline fun <T> MMKV.nullableDefaultValueDelegate( key: String? = null, defaultValue: T?, crossinline getter: MMKV.(String, T?) -> T, crossinline setter: MMKV.(String, T) -> Boolean ): ReadWriteProperty<Any, T> = object : ReadWriteProperty<Any, T> { override fun getValue(thisRef: Any, property: KProperty<*>): T = getter(key ?: property.name, defaultValue) override fun setValue(thisRef: Any, property: KProperty<*>, value: T) { setter(key ?: property.name, value) }} fun MMKV.byteArray( key: String? = null, defaultValue: ByteArray? = null ): ReadWriteProperty<Any, ByteArray> =nullableDefaultValueDelegate(key, defaultValue, MMKV::decodeBytes, MMKV::encode) fun MMKV.string(key: String? = null, defaultValue: String? = null): ReadWriteProperty<Any, String> =nullableDefaultValueDelegate(key, defaultValue, MMKV::decodeString, MMKV::encode) fun MMKV.stringSet( key: String? = null, defaultValue: Set<String>? = null ): ReadWriteProperty<Any, Set<String>> =nullableDefaultValueDelegate(key, defaultValue, MMKV::decodeStringSet, MMKV::encode) inline fun <reified T : Parcelable> MMKV.parcelable( key: String? = null, defaultValue: T? = null): ReadWriteProperty<Any, T> = object : ReadWriteProperty<Any, T> { override fun getValue(thisRef: Any, property: KProperty<*>): T = decodeParcelable(key ?: property.name, T::class.java, defaultValue) override fun setValue(thisRef: Any, property: KProperty<*>, value: T) { encode(key ?: property.name, value) }}

调用方法:
import android.os.Bundleimport android.util.Logimport androidx.appcompat.app.AppCompatActivityimport com.tanjiajun.mmkvdemo.Rimport com.tanjiajun.mmkvdemo.data.model.UserDataimport com.tanjiajun.mmkvdemo.utils.*import com.tencent.mmkv.MMKVclass MainActivity : AppCompatActivity() {private val mmkv: MMKV by lazy { MMKV.defaultMMKV() }private var boolean by mmkv.boolean(key = "boolean", defaultValue = false)private var int by mmkv.int(key = "int", defaultValue = 0)private var long by mmkv.long("long", 0L)private var float by mmkv.float(key = "float", defaultValue = 0.0F)private var double by mmkv.double(key = "double", defaultValue = 0.0)private var byteArray by mmkv.byteArray(key = "byteArray")private var string by mmkv.string(key = "string")private var stringSet by mmkv.stringSet(key = "stringSet")private var parcelable by mmkv.parcelable<UserData>("parcelable")override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) boolean = true int = 100 long = 100L float = 100F double = 100.0 byteArray = ByteArray(100).apply { for (i in 0 until 100) { set(i, i.toByte()) } } string = "李书生" stringSet = HashSet<String>().apply { for (i in 0 until 100) { add("第($i)个") } } parcelable = UserData(name = "李书生", gender = "男", age = 26) Log.i(TAG, "boolean:$boolean") Log.i(TAG, "int:$int") Log.i(TAG, "long:$long") Log.i(TAG, "float:$float") Log.i(TAG, "double:$double") Log.i(TAG, "byteArray:$byteArray") Log.i(TAG, "string:$string") Log.i(TAG, "stringSet:$stringSet") Log.i(TAG, "parcelable:$parcelable")}private companion object { const val TAG = "Lishusheng"}}

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