android-livedata - 如何使用liveData协程 block

Question

如何使用liveData协程 block

在官方文档

https://developer.android.google.cn/topic/libraries/architecture/coroutines#livedata

现在可以在 liveData block 中将 livedata 与协程一起使用

val user: LiveData<User> = liveData {
    val data = database.loadUser() // loadUser is a suspend function.
    emit(data)
}

当我尝试这样使用时

fun onLogin(v: View) {
    liveData(context = Dispatchers.IO) {
        val reqLogin = ReqLogin(account = account.value?:"", password = MD5(password.value?:""))
        val data = HttpManager.service(MobileApi::class.java).loginSuspend(reqLogin)
        emit(data.data!!)
    }
}

block 中的代码未执行

搜索发现liveData block 总是用于赋值

https://medium.com/androiddevelopers/viewmodels-and-livedata-patterns-antipatterns-21efaef74a54

如果想刷新实时数据值，可以使用类似的转换

LiveData<Repo> repo = Transformations.switchMap(repoIdLiveData, repoId -> {
    if (repoId.isEmpty()) {
        return AbsentLiveData.create();
    }
    return repository.loadRepo(repoId);
});

但是我该如何使用它 1. Activity onResume并从服务器刷新数据 2.一些点击事件触发请求并获取一些新数据来显示

在我的登录场景中，使用 viewModelScope 似乎更有用

fun onLogin(v: View) {
    val reqLogin = ReqLogin(account = account.value ?: "", password = MD5(password.value ?: ""))
    viewModelScope.launch {
        val data = withContext(Dispatchers.IO) {
            HttpManager.service(MobileApi::class.java).loginSuspend(reqLogin)
        }
        _userInfo.value = data.data!!
        _isLogin.value = true
    }
}

Answer 1

    fun onLogin(v: View) {
    liveData(context = Dispatchers.IO) {
        val reqLogin = ReqLogin(account = account.value?:"", password = MD5(password.value?:""))
        val data = HttpManager.service(MobileApi::class.java).loginSuspend(reqLogin)
        emit(data.data!!)
    }
}

代码块未执行，因为文档说明了

The code block starts executing when LiveData becomes active and is automatically canceled after a configurable timeout when the LiveData becomes inactive.

您应该通过观​​察它来使其活跃。