到现在为止，我已经快10天了，我在YouTube上搜索和观看视频来寻找答案，但我找不到它。如果可以的话请帮助我。
这里开始我的 MainActivity 代码：
class MainActivity : ComponentActivity() {
lateinit var appDB: AppDatabase
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MyVolleyTheme {
appDB = AppDatabase.getDatabase(this)
Surface(
modifier = Modifier
.fillMaxSize(),
color = MaterialTheme.colors.background
) {
Column(
horizontalAlignment = Alignment.CenterHorizontally,
modifier = Modifier
) {
Spacer(modifier = Modifier.height(30.dp))
val text1 = remember { mutableStateOf("") }
TextField(
modifier = Modifier
.height(60.dp)
.fillMaxWidth()
.padding(0.dp),
value = text1.value,
onValueChange = { nextText ->
text1.value = nextText
},
label = {
Text(
modifier = Modifier.padding(0.dp),
text = "LastName",
textAlign = TextAlign.Center,
fontSize = 13.sp
)
},
singleLine = true,
trailingIcon = {
IconButton(onClick = {
}) {
Icon(
imageVector = Icons.Filled.Face,
contentDescription = "lastName",
modifier = Modifier.size(25.dp)
)
}
},
keyboardOptions = KeyboardOptions(
keyboardType = KeyboardType.Text,
imeAction = ImeAction.Next
),
)
val text2 = remember { mutableStateOf("") }
TextField(
modifier = Modifier
.height(60.dp)
.fillMaxWidth()
.padding(0.dp),
value = text2.value,
onValueChange = { nextText ->
text2.value = nextText
},
label = {
Text(
modifier = Modifier.padding(0.dp),
text = "Age",
textAlign = TextAlign.Center,
fontSize = 13.sp
)
},
singleLine = true,
trailingIcon = {
IconButton(onClick = {
}) {
Icon(
imageVector = Icons.Filled.Person,
contentDescription = "Age",
modifier = Modifier.size(25.dp)
)
}
},
keyboardOptions = KeyboardOptions(
keyboardType = KeyboardType.Number,
imeAction = ImeAction.Done
),
)
Button(onClick = {
if (text1.value.isNotEmpty() && text2.value.isNotEmpty()) {
val example = User(null, text1.value, text2.value.toInt())
lifecycleScope.launch(Dispatchers.IO) {
appDB.userDao().insertAll(example)
}
Toast.makeText(
this@MainActivity,
"Data inserted successfully",
Toast.LENGTH_LONG
).show()
text1.value = ""
text2.value = ""
} else if (text1.value.isEmpty() || text2.value
.isEmpty()
) {
Toast.makeText(
this@MainActivity,
"Please fill the fields",
Toast.LENGTH_LONG
).show()
}
}) {
Text(text = "Save is database")
}
Spacer(modifier = Modifier.height(60.dp))
**// Showing a LazyColumn of our Database Content Here**
}
}
}
}
}
}
我的房间实体代码是：
@Entity(tableName = "user_table")
data class User(
@PrimaryKey(autoGenerate = true) val uid: Int?,
@ColumnInfo(name = "last_name") val lastName: String?,
@ColumnInfo(name = "age") val age: Int?
)
还有我的Room Dao：
@Dao
interface UserDao {
@Query("SELECT * FROM user_table")
fun getAll(): List<User>
@Query("SELECT * FROM user_table WHERE uid IN (:userIds)")
suspend fun loadAllByIds(userIds: IntArray): List<User>
@Query(
"SELECT * FROM user_table WHERE last_name LIKE :last AND " + "age LIKE :age LIMIT 1"
)
suspend fun findByNameAge(last: String, age: Int): User
@Insert
suspend fun insertAll(vararg users: User)
@Delete
suspend fun delete(user: User)
}
还有我的房间数据库：
@Database(entities = [User::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
companion object {
@Volatile
private var INSTANCE: AppDatabase? = null
fun getDatabase(context: Context): AppDatabase {
val tempInstance = INSTANCE
if (tempInstance != null) {
return tempInstance
}
synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
AppDatabase::class.java,
"user_database"
).build()
INSTANCE = instance
return instance
}
}
}
}
使用这些代码，我可以成功地将数据插入我的 Room 数据库。但如何在 lazycolumn 中显示我的数据库？
这是在 LazyColumn 中显示 Room 数据库表的基本代码：
// table:
@Entity(tableName = "word_table")
class Word(
@PrimaryKey @ColumnInfo(name = "word") val text: String
)
// DAO:
@Query("SELECT * FROM word_table ORDER BY word COLLATE NOCASE ASC")
fun getAlphabetizedWords(): Flow<List<Word>>
@Insert(onConflict = OnConflictStrategy.IGNORE)
suspend fun insert(word: Word)
// repository:
val allWords: Flow<List<Word>> = wordDao.getAlphabetizedWords()
suspend fun insert(word: Word) {
wordDao.insert(word)
}
// viewModel:
val allWords: LiveData<List<Word>> = repository.allWords.asLiveData()
fun insert(word: Word) = viewModelScope.launch {
repository.insert(word)
}
// simplified composable:
@Composable
fun WordList() {
val list by mWordViewModel.allWords.observeAsState(listOf())
LazyColumn() {
items(list) { word ->
Row() {
Text(word.text)
}
}
}
}
要显示从数据库到 lazyColumn 的所有记录，请从 DAO 类到存储库类调用 getAll() 方法。 在我的应用程序中，我使用了 coroutineScope 来从 DAO 调用方法到 Repository 类。
fun getAllEmployees() {
coroutineScope.launch(Dispatchers.IO) {
allEmployees.postValue(employeeDao.getAllEmployees())
}
}
将 getAllEmployees() 函数添加到 Repository 类后，我从 viewmodel 类访问它，如下所示：
@HiltViewModel
class HomeViewModel @Inject constructor(private val employeeRepository:
EmployeeRepository) :
ViewModel() {
fun getAllEmployees(){
employeeRepository.getAllEmployees()
}
现在，从 viewmodel 类调用 getAllEmployees() 到 mainActivity 类，如下所示：
homeViewModel.getAllEmployees()
val lazyListState = rememberLazyListState()
Scaffold(
topBar = {
CustomToolbar(title = stringResource(id = R.string.app_name), openDrawer)
},
content = {
val employeeList: List<Employee> by homeViewModel.employeeList.observeAsState(initial = listOf())
if (employeeList.isNotEmpty()) {
Surface(color = Color.White, modifier = Modifier.fillMaxSize()) {
LazyColumn(
modifier = Modifier.padding(vertical = 4.dp),
state = lazyListState
) {
items(items = employeeList) { emp ->
EmployeeCard(employee = emp, navController = navController)
}
}
}
} else {
Column(
modifier = Modifier
.fillMaxSize()
.padding(20.dp),
verticalArrangement = Arrangement.Center,
horizontalAlignment = Alignment.CenterHorizontally,
) {
Text(
"No employees onboarded yet.",
fontSize = 20.sp,
modifier = Modifier
.wrapContentWidth()
.wrapContentHeight(),
textAlign = TextAlign.Center
)
}
}
}
在此处查看 Github 演示：https://github.com/MansiKothari15/HRComposeApp。 在这里查看博客：https://medium.com/jetpack-composers/jetpack-compose-room-db-b7b23bd6b189