Room数据库问题：Spinner显示POJO结构而非目标货币数据如何解决？

方法1：重写实体类的toString()方法 #

修改CurrencyDatabaseModel，重写toString()方法直接返回货币代码：

@Entity(tableName = "currencies")
data class CurrencyDatabaseModel(
    @PrimaryKey @ColumnInfo(name = "currency_name") val currency: String
) {
    override fun toString(): String = currency
}

Spinner默认会调用列表项的toString()方法，重写后即可直接显示USD、EUR这类代码，无需改动其他Adapter逻辑。

方法2：在数据层直接返回货币代码列表 #

步骤1：修改DAO查询语句 #

直接查询货币名字段，返回字符串列表的Flow：

@Dao
interface CurrencyDAO {
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insertNewCurrency(databaseModel: CurrencyDatabaseModel)

    @Query("SELECT currency_name FROM currencies ORDER BY currency_name")
    fun getAllCurrencyCodes(): Flow<List<String>>
}

步骤2：更新仓库层 #

class CurrencyDatabaseRepository(private val currencyDAO: CurrencyDAO) {
    val allCurrencyCodes: Flow<List<String>> = currencyDAO.getAllCurrencyCodes()

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun insertNewCurrency(currencyDatabaseModel: CurrencyDatabaseModel){
        currencyDAO.insertNewCurrency(currencyDatabaseModel)
    }
}

步骤3：更新ViewModel #

class CurrencyDatabaseViewModel(private val currencyDatabaseRepository: CurrencyDatabaseRepository) :
ViewModel() {
    val allCurrencyCodes: LiveData<List<String>> = currencyDatabaseRepository.allCurrencyCodes.asLiveData()
}

后续Spinner的Adapter直接使用这个字符串列表即可。

方法3：自定义Spinner的ArrayAdapter #

如果不想修改实体类或数据层，可以自定义Adapter，在绑定视图时提取货币代码：

// 在Activity/Fragment中设置Spinner Adapter
val adapter = object : ArrayAdapter<CurrencyDatabaseModel>(
    this,
    android.R.layout.simple_spinner_item,
    // 此处传入ViewModel中的allCurrencies数据列表
    viewModel.allCurrencies.value ?: emptyList()
) {
    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
        val textView = super.getView(position, convertView, parent) as TextView
        textView.text = getItem(position)?.currency ?: ""
        return textView
    }

    override fun getDropDownView(position: Int, convertView: View?, parent: ViewGroup): View {
        val textView = super.getDropDownView(position, convertView, parent) as TextView
        textView.text = getItem(position)?.currency ?: ""
        return textView
    }
}
binding.spinner.adapter = adapter

内容的提问来源于stack exchange，提问作者OutCala