MMKV基本用法

2022-11-17 本文已影响0人加油小李

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

支持以下Java语言基础类型：
- boolean、int、long、float、double、byte[]
支持以下Java类和容器：
- String、Set<String>
- 任何发现Parcelable的类型

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.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import com.tanjiajun.mmkvdemo.R
import com.tanjiajun.mmkvdemo.data.model.UserData
import com.tanjiajun.mmkvdemo.utils.*
import com.tencent.mmkv.MMKV

class 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"
}
}

MMKV基本用法

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