Startup是什么

目前startup版本：1.0.0-alpha02。不建议现在用。
在应用程序启动时初始化组件简单、高效的方式。显示设置初始化顺序。
允许您定义共享单个内容提供程序组件初始化。不是每个需要初始化的组件定义单独的ContentProvider。显著提高应用程序启动时间。
ContentProvider的onCreate介于Application的attachBaseContext和onCreate之间。App Startup是建立在这个基础上封装。

简单使用

dependencies {
    implementation 'androidx.startup:startup-runtime:1.0.0-alpha02'
}

自动初始化

模拟三个库需要初始化SdkA、SdkB、SdkC

class SdkA {
    companion object{
        fun getInstance():SdkA{
            return Instance.instance
        }
    }
    private object Instance{
        val instance = SdkA()
    }
}
class SdkB {
    companion object{
        fun getInstance():SdkB{
            return Instance.instance
        }
    }
    private object Instance{
        val instance = SdkB()
    }
}
class SdkC {
    companion object{
        fun getInstance():SdkC{
            return Instance.instance
        }
    }
    private object Instance{
        val instance = SdkC()
    }
}

创建初始化对象

class SdkAInitializer : Initializer<SdkA> {
    companion object{
        private const val TAG = "startup-SdkAInit-"
    }
    override fun create(context: Context): SdkA {
        Log.d(TAG, "create: ")
        return SdkA.getInstance()
    }

    override fun dependencies(): MutableList<Class<out Initializer<*>>> {
        Log.d(TAG, "dependencies: ")
        return Collections.emptyList()
    }
}

class SdkBInitializer : Initializer<SdkB>{
    companion object{
        private const val TAG = "startup-SdkBInit-"
    }
    override fun create(context: Context): SdkB {
        Log.d(TAG, "create: ")
        return SdkB.getInstance()
    }

    override fun dependencies(): MutableList<Class<out Initializer<*>>> {
        Log.d(TAG, "dependencies: ")
        return mutableListOf(SdkAInitializer::class.java)
    }
}

class SdkCInitializer : Initializer<SdkC>{
    companion object{
        private const val TAG = "startup-SdkCInit-"
    }
    override fun create(context: Context): SdkC {
        Log.d(TAG, "create: ")
        return SdkC.getInstance()
    }

    override fun dependencies(): MutableList<Class<out Initializer<*>>> {
        Log.d(TAG, "dependencies: ")
        return mutableListOf(SdkBInitializer::class.java)
    }
}

oncreate方法进行对象初始化；dependencies 方法添加依赖关系；这里是C-->B-->A模拟的依赖关系
然后在清单文件配置InitializationProvider

        <provider
            android:name="androidx.startup.InitializationProvider"
            android:authorities="${applicationId}.androidx-startup"
            android:exported="false"
            tools:node="merge">
            <!--            自动初始化-->
            <meta-data
                android:name="com.example.myapplication.startup.SdkCInitializer"
                android:value="androidx.startup" />
        </provider>

手动初始化

创建SdkD ，SdkDInitializer

class SdkD {
    companion object{
        fun getInstance():SdkD{
            return Instance.instance
        }
    }
    private object Instance{
        val instance = SdkD()
    }
}

class SdkDInitializer : Initializer<SdkD>{
    companion object{
        private const val TAG = "startup-SdkDInit"
    }
    override fun create(context: Context): SdkD {
        Log.d(TAG, "create: ")
        return SdkD.getInstance()
    }

    override fun dependencies(): MutableList<Class<out Initializer<*>>> {
        Log.d(TAG, "dependencies: ")
        return Collections.emptyList()
    }
}

手动初始化清单配置

        <provider
            android:name="androidx.startup.InitializationProvider"
            android:authorities="${applicationId}.androidx-startup"
            android:exported="false"
            tools:node="merge">
            <!--            自动初始化-->
            <meta-data
                android:name="com.example.myapplication.startup.SdkCInitializer"
                android:value="androidx.startup" />
            <!--            手动初始化-->
            <meta-data
                android:name="com.example.myapplication.startup.SdkDInitializer"
                android:value="androidx.startup"
                tools:node="remove" />
        </provider>

在需要的地方手动初始化调用

AppInitializer.getInstance(this).initializeComponent(SdkDInitializer::class.java)

总结

App Startup提供了一个ContentProvider来运行的初始化，避免写在Application中，也避免每个库单独使用ContentProvider(Leack Canary2等第三方库)耗时问题。可以自定义初始化顺序，每个初始化依赖都要实现Initializer接口，会导致文件增多。目前还处于alpha版本。不建议现在使用到项目中。