安卓开发 compose 现在有一个List<Note> 要实现拖动排序功能jetpack room数据库 该如何实现?kotlin完整代码
时间: 2024-05-16 17:13:15 浏览: 14
您好,以下是实现安卓开发 compose 现在有一个List<Note> 要实现拖动排序功能jetpack room数据库的 kotlin 代码示例:
首先,您需要在 build.gradle 文件中添加以下依赖:
```
implementation "androidx.compose.foundation:foundation-layout:1.0.0-beta02"
implementation "androidx.compose.material:material:1.0.0-beta02"
implementation "androidx.compose.runtime:runtime-livedata:1.0.0-beta02"
implementation "androidx.compose.ui:ui:1.0.0-beta02"
implementation "androidx.compose.ui:ui-tooling:1.0.0-beta02"
implementation "androidx.room:room-runtime:2.3.0"
kapt "androidx.room:room-compiler:2.3.0"
```
然后,您可以使用 Jetpack Compose 实现一个可拖动的列表,并使用 Room 数据库存储和加载数据。以下是完整的 Kotlin 代码:
```
import androidx.compose.foundation.background
import androidx.compose.foundation.gestures.draggable
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.alpha
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.PrimaryKey
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
@Entity(tableName = "notes")
data class Note(
@PrimaryKey val id: Int,
@ColumnInfo(name = "text") val text: String,
@ColumnInfo(name = "position") var position: Int
)
@Dao
interface NoteDao {
@Query("SELECT * FROM notes ORDER BY position ASC")
fun getNotes(): LiveData<List<Note>>
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(note: Note)
@Update
suspend fun update(note: Note)
}
@Database(entities = arrayOf(Note::class), version = 2)
abstract class AppDatabase : RoomDatabase() {
abstract fun noteDao(): NoteDao
companion object {
private var instance: AppDatabase? = null
fun getInstance(context: Context): AppDatabase {
return instance ?: synchronized(this) {
instance ?: buildDatabase(context).also { instance = it }
}
}
private fun buildDatabase(context: Context): AppDatabase {
return Room.databaseBuilder(context, AppDatabase::class.java, "notes.db")
.addMigrations(object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("ALTER TABLE notes ADD COLUMN position INTEGER DEFAULT 0")
}
})
.build()
}
}
}
class NoteViewModel : ViewModel() {
private val appDatabase = AppDatabase.getInstance(MyApplication.context)
private val noteDao = appDatabase.noteDao()
private val _notes = MutableLiveData<List<Note>>()
init {
loadNotes()
}
fun getNotes(): LiveData<List<Note>> {
return _notes
}
fun addNote() {
viewModelScope.launch(Dispatchers.IO) {
val count = noteDao.getNotes().value?.size ?: 0
noteDao.insert(Note(count + 1, "Note ${count + 1}", count + 1))
}
}
fun updateNotePosition(note: Note, position: Int) {
viewModelScope.launch(Dispatchers.IO) {
note.position = position
noteDao.update(note)
}
}
private fun loadNotes() {
viewModelScope.launch(Dispatchers.IO) {
val notes = noteDao.getNotes().value ?: emptyList()
_notes.postValue(notes)
}
}
}
@Composable
fun NotesList(noteViewModel: NoteViewModel) {
val notes by noteViewModel.getNotes().observeAsState(listOf())
Column(modifier = Modifier.padding(16.dp)) {
Button(onClick = { noteViewModel.addNote() }) {
Text("Add Note")
}
for (i in notes.indices) {
val note = notes[i]
Box(
modifier = Modifier
.fillMaxSize()
.alpha(if (note.position == i) 1f else 0.5f)
.background(Color.White)
.draggable(
orientation = Orientation.Vertical,
onDragStarted = { /* Do nothing */ },
onDragStopped = { noteViewModel.updateNotePosition(note, it) }
)
) {
Text(
text = note.text,
modifier = Modifier.padding(16.dp)
)
}
}
}
}
class MainActivity : ComponentActivity() {
private val noteViewModel by viewModels<NoteViewModel>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
NotesList(noteViewModel)
}
}
}
```
代码说明:
1.定义 Note 实体类,其中包含 id、text 和 position 字段。
2.定义 NoteDao 接口,其中包含 getNotes()、insert() 和 update() 函数。
3.AppDatabase 是一个 Room 数据库,它包含 NoteDao。
4.NoteViewModel 是一个 ViewModel,它包含一个 LiveData 列表,用于存储 Note 对象列表。
5.NotesList 是一个 Composable 函数,它显示 Note 对象列表,并允许用户重新排序它们。
6.在主 Activity 中使用 NotesList Composable 函数。
该代码依赖于 Jetpack Compose 和 Room 数据库。Jetpack Compose 提供了一种简单的方法来实现可拖动的列表,而 Room 数据库用于保存和加载 Note 数据。