要解决使用适配器和回收视图器显示两个表在多对多关系中的数据的问题,可以按照以下步骤进行操作:
配置依赖项: 在 build.gradle 文件中添加以下依赖项:
implementation 'androidx.room:room-runtime:2.3.0'
implementation 'androidx.recyclerview:recyclerview:1.2.1'
annotationProcessor 'androidx.room:room-compiler:2.3.0'
创建实体类: 创建两个实体类,分别表示两个表,并添加相应的注解和关系标记。
@Entity(tableName = "table1")
data class Table1(
@PrimaryKey val id: Int,
val name: String
)
@Entity(tableName = "table2")
data class Table2(
@PrimaryKey val id: Int,
val name: String
)
@Entity(tableName = "table1_table2", primaryKeys = ["table1Id", "table2Id"])
data class Table1Table2(
val table1Id: Int,
val table2Id: Int
)
创建数据库类: 创建一个继承自 RoomDatabase 的类,并在其中定义数据库的表和版本号。
@Database(entities = [Table1::class, Table2::class, Table1Table2::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun table1Dao(): Table1Dao
abstract fun table2Dao(): Table2Dao
abstract fun table1Table2Dao(): Table1Table2Dao
companion object {
private var INSTANCE: AppDatabase? = null
fun getInstance(context: Context): AppDatabase {
if (INSTANCE == null) {
synchronized(AppDatabase::class) {
INSTANCE = Room.databaseBuilder(
context.applicationContext,
AppDatabase::class.java, "my-database"
).build()
}
}
return INSTANCE!!
}
}
}
创建数据访问对象(DAO): 创建三个接口,分别用于访问每个表的数据。
@Dao
interface Table1Dao {
@Query("SELECT * FROM table1")
fun getAll(): List
}
@Dao
interface Table2Dao {
@Query("SELECT * FROM table2")
fun getAll(): List
}
@Dao
interface Table1Table2Dao {
@Query("SELECT table1Id, table2Id FROM table1_table2 WHERE table1Id = :table1Id")
fun getTable2IdsForTable1(table1Id: Int): List
}
创建适配器: 创建一个适配器类,继承自 RecyclerView.Adapter,并在其中实现数据绑定和视图创建的逻辑。
class MyAdapter(private val context: Context) : RecyclerView.Adapter() {
private var data: List = emptyList()
private val db: AppDatabase = AppDatabase.getInstance(context)
class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
val textView: TextView = view.findViewById(R.id.textView)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.item_layout, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val table1 = data[position]
holder.textView.text = table1.name
val table1Table2Dao = db.table1Table2Dao()
val table2Ids = table1Table2Dao.getTable2IdsForTable1(table1.id)
// 根据 table2Ids 加载 table2 的数据,并进行相应的处理
// ...
}
override fun getItemCount(): Int {
return data.size
}
fun setData(data: List) {
this.data = data
notifyDataSetChanged()
}
}
设置 RecyclerView: 在 Activity 或 Fragment 中设置 RecyclerView,并将适配器与 RecyclerView 绑定。
class MainActivity : AppCompatActivity() {
private lateinit var recyclerView: RecyclerView
private lateinit var adapter: MyAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout