将 LiveData 获取到 ViewModel

Question

我想在我的 ViewModel 中访问 LiveData。问题是 LiveData<String?> 需要访问 activity 才能计算。这就是我计算 String.

的方式

suspend fun Fragment.getAuthToken(): String? {
    val am: AccountManager = AccountManager.get(activity)
    val accounts: Array<out Account> = am.getAccountsByType(getAccountType())
    return accounts.firstOrNull()?.let {
         withContext(Dispatchers.IO) {
            am.blockingGetAuthToken(it, getAccountType(), true)
        }
    }
}

然后像这样从我的 fragment 计算 LiveData：

val authTokenLiveData: LiveData<String?> = liveData {
   emit(getAuthToken())
}

请帮助我访问 ViewModel 中的 LiveData 或者告诉我如何从 ViewModel.

中计算它

Answer 1

感谢 Nicolas，我找到了解决问题的方法。

步骤 1. 创建 ViewModelFactory:

@Suppress("UNCHECKED_CAST")
class AccountViewModelFactory(private val accountManager: AccountManager, private val repository: UserRepository) :
    ViewModelProvider.NewInstanceFactory() {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T =
        AccountViewModel(accountManager, repository) as T
}

步骤 2. 从 Fragment 初始化 ViewModel:

private val accountViewModel: AccountViewModel by viewModels {
     AccountViewModelFactory(getAccountManager(), getUserRepository())
}

第 3 步。创建 ViewModel 并从 ViewModel 创建 LiveData：

class AccountViewModel(private val accountManager: AccountManager, private val repository: UserRepository) : ViewModel() {
    val authTokenLiveData: LiveData<String?> = liveData {
        emit(accountManager.myAuthToken())
    }
}

第 4 步。创建 myAuthToken() 和 getAccountManager() 扩展函数。

fun Fragment.getAccountManager() : AccountManager = AccountManager.get(activity)

suspend fun AccountManager.myAuthToken(): String? {
    val accounts: Array<out Account> = getAccountsByType(accountType)
    return accounts.firstOrNull()?.let {
         withContext(Dispatchers.IO) {
            blockingGetAuthToken(it, accountType, true)
        }
    }
}

将 LiveData 获取到 ViewModel

Getting LiveData to the ViewModel

android

kotlin

android-viewmodel