如何使用视图模型和实时数据将参数传递给我的Word Dao进行查询

Question

更新：如何使用ViewModelFactory，是否有必要使用它来传递我们的参数？有什么好处？这会打破实时数据的概念吗？

我想把一个参数发送到我房间数据库的word Dao中进行查询，但在我的情况下，我不知道如何传递这个参数。让我们从代码开始。。。WordDao.kt

@Dao
interface WordDao {
@Insert
fun insert(word: Word)
@Update
fun update(word: Word)
@Delete
fun delete(word: Word)
@Query("delete from En_Fa")
fun deleteAllNotes()
@Query("SELECT * FROM En_Fa ORDER BY id ASC")
fun getAllNotes(): LiveData<List<Word>>
@Query("Select * From En_Fa WHERE date == :today ")
fun getTodayWords(today: String): LiveData<List<Word>>
}

WordRepository.kt

class WordRepository(private val wordDao: WordDao, today: String) {
val readAllData: LiveData<List<Word>> = wordDao.getAllNotes()
val readToday: LiveData<List<Word>> = wordDao.getTodayWords(today)

fun addWord(word: Word) {
wordDao.insert(word)
}
}

WordViewModel.kt

class WordViewModel(application: Application): AndroidViewModel(application) {
val readAllData2: LiveData<List<Word>>
private val repository: WordRepository
init {
val wordDao = WordDatabase.getInstance(application).wordDao()
repository = WordRepository(wordDao, today)
readAllData2 = repository.readToday
}
fun addWord(word: Word){
viewModelScope.launch(Dispatchers.IO){
repository.addWord(word)
}
}
}

这是我的代码行，它在我的片段中创建了这个wordview模型类的对象

private val mWordViewModel: WordViewModel by viewModels()

那么如何将我的(今天(变量从我的片段传递到我的WordViewModel类

Answer 1

我想你正在寻找这个：

@Dao
interface WordDao {
// ...
@Query("Select * From En_Fa WHERE date == :today ")
fun getTodayWords2(today: String): <List<Word>
}

然后在存储库中：

class WordRepository{
// ... ...
var mutableWords: MutableLiveData<List<Word>> = MutableLiveData()
fun getWords(today: String): List<Word> {  // WARNING! run this in background thread else it will crash
return wordDao.getTodayWords2(today)
}
fun getWordsAsync(today: String) {
Executors.newSingleThreadExecutor().execute { 
val words = getWords(today)
liveWords.postValue(words)   // <-- just doing this will trigger the observer and do next thing, such as, updating ui
}
}
}

然后在您的视图中模型：

class WordViewModel(application: Application): AndroidViewModel(application) {
// ... ...
val liveWords: LiveData<List<Word>> = repository.mutableWords
fun getWordsAsync(today: String) {
repository.getWordsAsync(today)
}
}

最后进入你的活动/片段：

fun viewModelDemo() {
mWordViewModel.liveWords.observe(this, Observer{
// todo: update the ui, eg
someTextView.text = it.toString()    // <-- here you get the output
})

someButton.setOnClickListener{
// here you give the input
mWordViewModel.getWordsAsync(today)  // get `today` from date picker or something    
}
}

编辑

所以您有一个带有适配器的recyclerView。当数据集发生更改时，可以调用notifyDataSetChanged。假设适配器如下所示：

class MyAdapter: RecyclerView.Adapter<ViewHolder> {
private var words: List<Word> = ArrayList() // initially points to an empty list
override fun getCount() { return words.size }
// ... ... other methods
// public method:
fun submitList(words1: List<Word>) {
this.words = words1  // so now it points to the submitted list
this.notifyDataSetChanged()  // this tells recyclerView to update itself
}  
}

然后在你的活动或片段中：

private lateinit var myAdapter: MyAdapter
override fun onCreate() {  // or onViewCreated if using fragment
// ... ... some codes
this.myAdapter = MyAdapter()
binding.recyclerView.adapter = myAdapter
viewModelDemo()
}
fun viewModelDemo() {
mWordViewModel.liveWords.observe(this, Observer{
// todo: update the ui, eg
myAdapter.submitList(it)    // <----- Here you call the submitList method
// <-- here you get the output
})
// --- ---
}

我希望这能奏效。

Answer 2

如果我答对了你的问题，那么，首先，您需要制作一个函数，返回要观察的liveData对象，然后您需要使用ViewModelProviders，在片段中为您提供ViewModel的对象。

mWordViewModel: WordViewModel = ViewModelProvider(this/getActivity()).get(WordViewModel::class.java)
mWordViewModel.getLiveDataFunction().observe(this/lifeCycleOwner, {
process result/response here
}

然后简单地使用。

mWordViewModel.addWord(today)