[ANR] 优化SharedPreference apply引起

前一篇文章[ANR]为什么SharedPreference会引起ANR，我们知道， SharedPreference的apply方法虽然是异步写入文件的，但是会在Activity和Service生命周期方法调用的时候，等待所有的写入完成，可能引起卡顿和ANR。

解决方法

为了快速解决这个问题，我们可以通过代理系统SharedPreference的所有apply方法，改为直接在子线程调用commit，即可。下面看代码。ps：以下代码可以直接复制使用。

class NoMainThreadWriteSharedPreferences private constructor(private val sysPrefs: SharedPreferences, val name: String) :
    SharedPreferences {

    private val preferencesCache: MutableMap<String, Any?> = HashMap()

    companion object {
        private val executor: ExecutorService = Executors.newSingleThreadExecutor()
        private val INSTANCES: MutableMap<String, NoMainThreadWriteSharedPreferences> = HashMap()

        @JvmStatic
        fun getInstance(sharedPreferences: SharedPreferences, name: String): SharedPreferences {
            return INSTANCES.getOrPut(name, { NoMainThreadWriteSharedPreferences(sharedPreferences, name) })
        }

        @VisibleForTesting
        @JvmStatic
        fun reset() {
            INSTANCES.clear()
        }
    }

    init {
        // 初始化的时候，缓存所有的键值对，也可以等到调用getBoolean等获取key方法的时候，再做
        preferencesCache.putAll(sysPrefs.all)
    }

    override fun contains(key: String?) = preferencesCache[key] != null

    override fun getAll() = HashMap(preferencesCache)

    override fun getBoolean(key: String, defValue: Boolean): Boolean {
        return preferencesCache[key] as Boolean? ?: defValue
    }

    override fun getInt(key: String, defValue: Int): Int {
        return preferencesCache[key] as Int? ?: defValue
    }

    override fun getLong(key: String, defValue: Long): Long {
        return preferencesCache[key] as Long? ?: defValue
    }

    override fun getFloat(key: String, defValue: Float): Float {
        return preferencesCache[key] as Float? ?: defValue
    }

    override fun getStringSet(key: String, defValues: MutableSet<String>?): MutableSet<String>? {
        @Suppress("UNCHECKED_CAST")
        return preferencesCache[key] as MutableSet<String>? ?: defValues
    }

    override fun getString(key: String, defValue: String?): String? {
        return preferencesCache[key] as String? ?: defValue
    }

    override fun edit(): SharedPreferences.Editor {
        return Editor(sysPrefs.edit())
    }

    override fun registerOnSharedPreferenceChangeListener(listener: SharedPreferences.OnSharedPreferenceChangeListener) {
        sysPrefs.registerOnSharedPreferenceChangeListener(listener)
    }

    override fun unregisterOnSharedPreferenceChangeListener(listener: SharedPreferences.OnSharedPreferenceChangeListener) {
        sysPrefs.unregisterOnSharedPreferenceChangeListener(listener)
    }

    inner class Editor(private val sysEdit: SharedPreferences.Editor) : SharedPreferences.Editor {

        private val modifiedData: MutableMap<String, Any?> = HashMap()
        private var keysToRemove: MutableSet<String> = HashSet()
        private var clear = false

        override fun commit(): Boolean {
            submit()
            return true
        }

        // apply和commit都调用submit方法
        override fun apply() {
            submit()
        }

        private fun submit() {
            synchronized(preferencesCache) {
                // 先更新到本地的内存缓存
                storeMemCache()
                // 再用异步线程，调用系统commit方法去更新
                queuePersistentStore()
            }
        }

        private fun storeMemCache() {
            if (clear) {
                preferencesCache.clear()
                clear = false
            } else {
                preferencesCache.keys.removeAll(keysToRemove)
            }
            keysToRemove.clear()
            preferencesCache.putAll(modifiedData)
            modifiedData.clear()
        }

        private fun queuePersistentStore() {
            try {
                executor.submit {
                    sysEdit.commit()
                }
            } catch (ex: Exception) {
            }
        }

        override fun remove(key: String): SharedPreferences.Editor {
            keysToRemove.add(key)
            modifiedData.remove(key)
            sysEdit.remove(key)
            return this
        }

        override fun clear(): SharedPreferences.Editor {
            clear = true
            sysEdit.clear()
            return this
        }

        override fun putLong(key: String, value: Long): SharedPreferences.Editor {
            modifiedData[key] = value
            sysEdit.putLong(key, value)
            return this
        }

        override fun putInt(key: String, value: Int): SharedPreferences.Editor {
            modifiedData[key] = value
            sysEdit.putInt(key, value)
            return this
        }

        override fun putBoolean(key: String, value: Boolean): SharedPreferences.Editor {
            modifiedData[key] = value
            sysEdit.putBoolean(key, value)
            return this
        }

        override fun putStringSet(key: String, values: MutableSet<String>?): SharedPreferences.Editor {
            modifiedData[key] = values
            sysEdit.putStringSet(key, values)
            return this
        }

        override fun putFloat(key: String, value: Float): SharedPreferences.Editor {
            modifiedData[key] = value
            sysEdit.putFloat(key, value)
            return this
        }

        override fun putString(key: String, value: String?): SharedPreferences.Editor {
            modifiedData[key] = value
            sysEdit.putString(key, value)
            return this
        }
    }
}

使用的时候，通过在自定义的Application和BaseActivity中，修改getSharedPreferences方法，将我们的类作为系统SharedPreference的包装类返回。

public SharedPreferences getSharedPreferences(String name, int mode) {
  return NoMainThreadWriteSharedPreferences.getInstance(super.getSharedPreferences(name, mode), name);
}

总结

优点：

• 可以快速修复Activity和Service生命周期onStart和onPause方法，等待SharedPreference写入文件的ANR问题

缺点：

• onSharedPreferenceChangeListener的回调会变慢，本来只需要等到写入内存缓存即可回调，现在需要等待真正写入文件才能回调

待解决问题：

• 如果用户调用commit和apply多次，还是会写入多次，不会合并请求，且SharedPreference的写入都是完整文件的写入
• 没有解决调用getBoolean等方法获取value时，等待SharedPreference读到缓存，引起的ANR问题
• 没有解决getPreferencesDir引起的ANR问题