JetPack

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1. Android Jetpack 架构组件之 Lifecycle（使用篇）
https://blog.csdn.net/Alexwll/article/details/80638905

2. Android Jetpack 架构组件之 Lifecycle（源码篇）
https://blog.csdn.net/Alexwll/article/details/82491901

3. Android Jetpack 架构组件之 ViewModel （源码篇）
https://blog.csdn.net/Alexwll/article/details/82459614

4. Android Jetpack 架构组件之 LiveData（使用、源码篇）
https://blog.csdn.net/Alexwll/article/details/82996003

5. Android Jetpack架构组件之 Paging（使用、源码篇）
https://blog.csdn.net/Alexwll/article/details/83246201

6. Android Jetpack 架构组件之 Room（使用、源码篇）
https://blog.csdn.net/Alexwll/article/details/83033460

7. Android Jetpack 架构组件之Navigation
https://blog.csdn.net/Alexwll/article/details/83244004

8. Android Jetpack架构组件之WorkManger
https://blog.csdn.net/Alexwll/article/details/83244871

即学即用 Android Jetpack - ViewModel & LiveData - 简书

LiveData is an observable data holder class. Unlike a regular observable, LiveData is lifecycle-aware, meaning it respects the lifecycle of other app components, such as activities, fragments, or services.

The ViewModel class is designed to store and manage UI-related data in a lifecycle conscious way. The ViewModel class allows data to survive configuration changes such as screen rotations.

可以通过下面的图来看 ViewModel 和 LiveData 之间的关系

还可以通过下面的代码来看 ViewModel 和 LiveData 之间的关系

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class ShoeModel constructor(shoeRepository: ShoeRepository) : ViewModel() {

    // 品牌的观察对象 默认观察所有的品牌
    private val brand = MutableLiveData<String>().apply {
        value = ALL
    }

    // 鞋子集合的观察类
    val shoes: LiveData<List<Shoe>> = brand.switchMap {
        // Room数据库查询，只要知道返回的是LiveData<List<Shoe>>即可
        if (it == ALL) {
            shoeRepository.getAllShoes()
        } else {
            shoeRepository.getShoesByBrand(it)
        }
    }

    fun setBrand(brand:String){
        this.brand.value = brand

        this.brand.map {

        }
    }

    fun clearBrand(){
        this.brand.value = ALL
    }

    companion object {
        private const val ALL = "所有"
    }
}

验证 LiveData 的在两个 fragments 上共享数据

源码

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// LoginLiveData
class LoginLiveData : MutableLiveData<LoginInfo>() {

    companion object {
        private lateinit var sInstance: LoginLiveData

        @MainThread
        fun get(): LoginLiveData {
            sInstance = if (::sInstance.isInitialized) sInstance else LoginLiveData()
            return sInstance
        }
    }
}

// LoginFragment.onViewCreated
Log.e("TTAG", "from LoginFragment, the init liveData is: ${LoginLiveData.get().value}")
LoginLiveData.get().observe(viewLifecycleOwner, Observer {
    Log.e("TTAG", "from LoginFragment, the liveData changed: $it")
})
Handler().postDelayed({
    LoginLiveData.get().apply {
        value = LoginInfo("login", "login", "login@qq.com")
    }
}, 2000)

// WelcomeFragment.onViewCreated
Log.e("TTAG", "from LoginFragment, the init liveData is: ${LoginLiveData.get().value}")
LoginLiveData.get().observe(viewLifecycleOwner, Observer {
    Log.e("TTAG", "from LoginFragment, the liveData changed: $it")
})
Handler().postDelayed({
    LoginLiveData.get().apply {
        value = LoginInfo("login", "login", "login@qq.com")
    }
}, 2000)

日志

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# 首次进入welcome
E/TTAG: from WelcomeFragment, the init liveData is: null
E/TTAG: from WelcomeFragment, the liveData changed:LoginInfo(account=welcome, pwd=welcome, email=welcome@qq.com)
# 点击进入login
E/TTAG: from LoginFragment, the init liveData is: LoginInfo(account=welcome, pwd=welcome, email=welcome@qq.com)
E/TTAG: from LoginFragment, the liveData changed: LoginInfo(account=welcome, pwd=welcome, email=welcome@qq.com)
E/TTAG: from LoginFragment, the liveData changed: LoginInfo(account=login, pwd=login, email=login@qq.com)

Room

即学即用 Android Jetpack - Room - 简书

Android Room 框架学习 - 简书

Paging

问题： Jetpack Paging 闪烁

描述： 一点点的不相关的修改都会导致列表刷新，源码如下

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companion object {
    val DIFF_CALLBACK = object : DiffUtil.ItemCallback<DbFlowDay>() {
        override fun areItemsTheSame(oldItem: DbFlowDay, newItem: DbFlowDay): Boolean {
            return oldItem === newItem
        }
        override fun areContentsTheSame(oldItem: DbFlowDay, newItem: DbFlowDay): Boolean {
            return oldItem.day == newItem.day
        }
    }
}

解决，如下源码：

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companion object {
    val DIFF_CALLBACK = object : DiffUtil.ItemCallback<DbFlowDay>() {
        override fun areItemsTheSame(oldItem: DbFlowDay, newItem: DbFlowDay): Boolean {
            return oldItem.id == newItem.id // ！！！ 这里，比较id，而不是对象
        }
        override fun areContentsTheSame(oldItem: DbFlowDay, newItem: DbFlowDay): Boolean {
            return oldItem.day == newItem.day
        }
    }
}

databinding recyclerView

DataBinding 在 RecyclerView 中的使用 - 简书