如何從一個活動中獲取 edittext 值到下一個活動的 recyclerview？

Question

我正在嘗試從一項活動中獲取 edittext 值並在 recycleview 中顯示該文本並使用 room DB 進行存儲....

基本上這個想法是在點擊時在活動地址中添加地址，加上它將重定向到下一頁，用戶在提交時獲取地址表單，它將獲取地址並添加到以前的活動回收視圖。

這是我的房間代碼：

桌子： - -

@Entity(tableName = "address")
class Address {
@PrimaryKey
var id = 0

@ColumnInfo(name = "address")
var address: String? = null
}

數據庫：-

@Database(entities = [Address::class], version = 1)
 abstract class Database : RoomDatabase() {
abstract fun AddressDao(): AddressDao
}

地址道：

@Dao
interface AddressDao {
@Insert
suspend fun addData(address: Address)



@Query("select * from address")
fun getAddressesWithChanges() :LiveData<List<Address>>

@Query("SELECT EXISTS (SELECT 1 FROM address WHERE id=:id)")
suspend fun isAddressAdded(id: Int): Int

@Delete
suspend fun delete(address: Address)
}

AddAddressActivity 活動：

   class AddAddressActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.addaddress)

    val editText: EditText = findViewById(R.id.longaddress)

    val application = application as CustomApplication

    saveaddress.setOnClickListener {
        val address = Address()
        address.address = editText.getText().toString()

        lifecycleScope.launch {
            application.addressDao.addData(address)
            finish()
           }
         }
       }
      }

地址活動：-

     class AddressActivity : AppCompatActivity() {
      private val adapter = AddressAdapter()

     private lateinit var data: LiveData<List<Address>>

     override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.address)

    addbutton.findViewById<View>(R.id.addbutton).setOnClickListener {
        val intent = Intent(this, AddAddressActivity::class.java)
        startActivity(intent)
    }

    val recyclerView = findViewById<RecyclerView>(R.id.recyclerview)
    recyclerView.setHasFixedSize(true)
    recyclerView.layoutManager = LinearLayoutManager(this, 
    LinearLayoutManager.VERTICAL, false)
    recyclerView.adapter = adapter

    val application = application as CustomApplication
    data = application.database.AddressDao().getAddressesWithChanges()
    data.observe(this, Observer { words1 ->
        // Update the cached copy of the words in the adapter.
        words1?.let { adapter.updateData(it) }})


}
  }

地址適配器活動：-

class AddressAdapter: RecyclerView.Adapter<AddressAdapter.ViewHolder>() {
private var addresses: List<Address> = Collections.emptyList()

override fun onCreateViewHolder(viewGroup: ViewGroup, itemViewType: Int): 
   ViewHolder =
  ViewHolder(LayoutInflater.from(viewGroup.context)
  .inflate(R.layout.address_item, viewGroup, false) )

override fun onBindViewHolder(viewHolder: ViewHolder, position: Int) {
    val fl: Address = addresses[position]
    viewHolder.tv.setText(fl.address)
}

override fun getItemCount(): Int = addresses.size

inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    var tv: TextView

    init {
        tv = itemView.findViewById(R.id.ftv_name)
    }    }

fun updateData(addresses:
               List<Address>) {
    this.addresses = addresses
    notifyDataSetChanged() // TODO: use ListAdapter if animations are needed
}

}

自定義應用：

class CustomApplication: Application() {
lateinit var database: Database
    private set
lateinit var addressDao: AddressDao
    private set

override fun onCreate() {
    super.onCreate()

    this.database = Room.databaseBuilder<Database>(
        applicationContext,
        Database::class.java, "database"
    ).build()

}

}

返回地址活動時，列表不顯示回收視圖為空

請幫助..我是 kotlin 和房間 db 的新手..

Answer 1

 abstract fun AddressDao(): AddressDao?

為什么這個可以為空？

 val favoriteData: List<Table>?

為什么這個可以為空？

 fun addData(favoriteList: Table?)

為什么這個可以為空？

 fun delete(favoriteList: Table?)

為什么這個可以為空？

---

類型化可空性使您能夠表示給定值可以是 null 的位置，從某種意義上說，它不存在是有意義的。

以上兩種情況都不代表這種情況。 Room 永遠不會返回給你null而不是實際的dao 。

Kotlin 的 null 安全性允許您通過使其成為類型系統的一部分來消除潛在的錯誤情況，它不應該被用來創建諸如此類的“假”錯誤情況。 如果您嘗試將null添加到數據庫而不是真正的 object，則您的代碼中可能存在錯誤，而 Kotlin 應該能夠幫助您消除這種可能性。

---

---

至於您的實際問題，您在濫用 Room。

.allowMainThreadQueries()是一種禁用錯誤檢查的方法，但該錯誤是有原因的。 您不應該在 UI 線程上讀取數據，因為如果有足夠的數據，您的應用就會凍結 (ANR)。

該代碼應該看起來像這樣：

@Entity(tableName = "address")
class Address {
    @PrimaryKey
    var id = 0

    @ColumnInfo(name = "address")
    var address: String? = null
}

數據庫：-

@Database(entities = [Address::class], version = 1)
abstract class Database : RoomDatabase() {
    abstract fun addressDao(): AddressDao
}

地址道：

@Dao
interface AddressDao {
    @Insert
    suspend fun addData(address: Address)

    @Query("select * from address")
    fun getAddressesWithChanges(): LiveData<List<Address>>

    @Query("SELECT EXISTS (SELECT 1 FROM address WHERE id=:id)")
    suspend fun isAddressAdded(id: Int): Int

    @Delete
    suspend fun delete(address: Address)
}


class CustomApplication: Application() {
    lateinit var database: Database
        private set
    lateinit var addressDao: AddressDao
        private set
    
    override fun onCreate() {
        super.onCreate()

        this.database = Room.databaseBuilder<Database>(
            applicationContext,
            Database::class.java, "database"
        ).build()

        addressDao = database.addressDao()
    }
}

AndroidManifest.xml

<application android:name=".CustomApplication"
    ...

地址活動：

import androidx.lifecycle.observe

class AddressActivity : AppCompatActivity() {
    private val adapter = AddressAdapter()

    private lateinit var data: LiveData<List<Address>>

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.address_activity)
 
        findViewById<View>(R.id.addButton).setOnClickListener {
            val intent = Intent(this, AddAddressActivity::class.java)
            startActivity(intent)
        }

        val recyclerView = findViewById<RecyclerView>(R.id.recyclerview)
        recyclerView.setHasFixedSize(true)
        recyclerView.layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)
        recyclerView.adapter = adapter

        val application = application as CustomApplication
        val addressDao = application.addressDao 

        data = addressDao.getAddressesWithChanges()
        data.observe(this) {
            adapter.updateData(it)
        }
    }
}

地址適配器：

class AddressAdapter: RecyclerView.Adapter<AddressAdapter.ViewHolder>() {
    private var addresses: List<Table> = Collections.emptyList()

    override fun onCreateViewHolder(viewGroup: ViewGroup, itemViewType: Int): ViewHolder =
        ViewHolder(LayoutInflater.from(viewGroup.context).inflate(R.layout.address_item, viewGroup, false))

    override fun onBindViewHolder(viewHolder: ViewHolder, position: Int) {
        val address = addresses[position]
        viewHolder.tv.setText(address.address)
    }

    override fun getItemCount(): Int = addresses.size

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val tv = itemView.findViewById(R.id.ftv_name)
    }

    fun updateData(addresses: List<Address>) {
        this.addresses = addresses
        notifyDataSetChanged() // TODO: use ListAdapter if animations are needed
    }
}

添加地址活動：-

class AddAddressActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.addaddress)

        val editText: EditText = findViewById(R.id.longaddress)

        val application = application as CustomApplication
        val addressDao = application.addressDao
        
        saveaddress.setOnClickListener {
            val address = Address()
            address.address = editText.getText().toString()

            lifecycleScope.launch {
                addressDao.addData(address)
                finish()
            }
        }
    }
}

您也可以參考https://codelabs.developers.google.com/codelabs/android-room-with-a-view-kotlin/#6

Answer 2

請將您的行替換為

  val  rv=findViewById<RecyclerView>(R.id.recyclerview)

您傳遞了錯誤的 id 地址 recyclerview 這就是它分配addressrecyclerview的null