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android - 获取 LiveData 到 ViewModel

问题描述

我想LiveData在我的ViewModel. 问题是LiveData<String?>需要访问activity才能进行计算。这就是我计算String.

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)
        }
    }
}

然后像这样计算LiveData我的fragment：

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

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

标签： androidkotlinandroid-viewmodel

解决方案

感谢 Nicolas，我已经能够找到解决问题的方法。

步骤 1. 创建一个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
}

ViewModel步骤 2.从初始化Fragment：

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

步骤 3. 创建ViewModel并LiveData从ViewModel:

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

步骤 4. 创建myAuthToken()和getAccountManager()扩展功能。

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)
        }
    }
}

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