如何从房间数据库android Kotlin获取回调

我只想从房间数据库中获取行计数作为Int值， 不是来自初始化的

LiveData

，例如

LiveData.value？.size

Dao类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

存储库类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

视图模型类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

这就是我想要的。但正如您所知，我们需要在后台线程而不是主线程访问房间数据库

所以我把代码改成

Dao类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

存储库类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

视图模型类

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

如果行计数为1，如何获取“1”作为回调？

使用计数

@Query("SELECT COUNT(column_name or primary key column name) from table_name ")
fun getCount(): Long

---

从存储库调用

getCount（）

我不确定。但您可以将myRepository.getUserCount（）的结果放入变量中，然后在当前启动中使用它来调用某些函数。Locat说“无法访问主线程上的数据库，因为它可能会长时间锁定UI。”在

getCount

块中添加

suspend

关键字，然后从

launch

块调用