Android Activity 之间共享的 ViewModel

• 
  
• 提供一个 Application 作用域的 ViewModel 去实现
  
• 要尽量避免被滥用
  
• 按需考虑加数据销毁、资源释放的逻辑
  

AppSharedViewModel

class AppSharedViewModel: ViewModel() {
var testLiveData = MutableLiveData(0)

}

class AppApplication : Application(), ViewModelStoreOwner {
companion object {
private lateinit var sInstance: AppApplication
fun getInstance() = sInstance

    }

override fun onCreate() {
super.onCreate()

        sInstance = this

    }

private val appSharedViewModelStore by lazy {

        ViewModelStore()

    }

override fun getViewModelStore(): ViewModelStore {
return appSharedViewModelStore

    }

}

    override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
//使用
val appSharedViewModel = ViewModelProvider(AppApplication.getInstance())[AppSharedViewModel::class.java]

    }

让 AppSharedViewModel 继承自 AndroidViewModel

class AppSharedViewModel(application: Application) : AndroidViewModel(application) {
var testLiveData = MutableLiveData(0)

}

• 
  
• 方案1
  

改写 ViewModel 创建获取的地方传入 AndroidViewModelFactory 实例

val appSharedViewModel = ViewModelProvider(

            AppApplication.getInstance(),

            ViewModelProvider.AndroidViewModelFactory.getInstance(AppApplication.getInstance())

        )[AppSharedViewModel::class.java]

• 
  
• 方案2
  

改写 Application 实现 HasDefaultViewModelProviderFactory 接口，因为 ViewModelProvider 构造方法里有调用 ViewModelProvider.AndroidViewModelFactory.defaultFactory 方法传入 ViewModelStoreOwner 去判断处理 HasDefaultViewModelProviderFactory 接口的逻辑

class AppApplication : Application(), ViewModelStoreOwner, HasDefaultViewModelProviderFactory {
companion object {
private lateinit var sInstance: AppApplication
fun getInstance() = sInstance

    }

override fun onCreate() {
super.onCreate()

        sInstance = this

    }

private val appSharedViewModelStore by lazy {

        ViewModelStore()

    }

override fun getViewModelStore(): ViewModelStore {
return appSharedViewModelStore

    }

override fun getDefaultViewModelProviderFactory(): ViewModelProvider.Factory {
return ViewModelProvider.AndroidViewModelFactory.getInstance(this)

    }

}