Android室沒有返回任何與url作爲參數

我試圖通過Feed的主鍵像這樣訪問項目列表。主鍵是一個url。試圖像這樣訪問它會讓我回退，並且將:arg0放在引號中會造成編譯時錯誤error: Unused parameter: arg0。有沒有可能使用此查詢的網址？Android室沒有返回任何與url作爲參數

@Query("SELECT * FROM item WHERE feed_url = :arg0") 
fun observeAllByFeed(feedUrl: String): LiveData<List<Item>>

項目

@Entity(foreignKeys = arrayOf(ForeignKey(
     entity = Feed::class, 
     parentColumns = arrayOf("url"), 
     childColumns = arrayOf("feed_url")))) 
data class Item(
     @ColumnInfo(name = "guid") @PrimaryKey var guid: String = "", 
     @ColumnInfo(name = "categoryIds") var categoryIds: List<Int> = emptyList(), 
     @ColumnInfo(name = "comments") var comments: String? = null, 
     @ColumnInfo(name = "content") var content: String? = null, 
     @ColumnInfo(name = "description") var description: String = "", 
     @ColumnInfo(name = "author") var author: String = "", 
     @ColumnInfo(name = "block") var block: Boolean = false, 
     @ColumnInfo(name = "duration") var duration: Int = 0, 
     @ColumnInfo(name = "explicit") var explicit: String = "", 
     @ColumnInfo(name = "image_url") var imageUrl: String = "", 
     @ColumnInfo(name = "keywords") var keywords: List<String> = emptyList(), 
     @ColumnInfo(name = "subtitle") var subTitle: String = "", 
     @ColumnInfo(name = "summary") var summary: String = "", 
     @ColumnInfo(name = "link") var link: String = "", 
     @ColumnInfo(name = "publication_date") var pubDate: Date = Date(), 
     @ColumnInfo(name = "title") var title: String = "", 
     @ColumnInfo(name = "feed_url") var feedURL: String = "", 
     @ColumnInfo(name = "download_state") var downloadState: Int = Item.DownloadState.STATE_NOT_DOWNLOADED 
) : Serializable { 
    companion object DownloadState { 
     val STATE_NOT_DOWNLOADED = 0 
     val STATE_DOWNLOADING = 1 
     val STATE_DOWNLOADED = 2 
    } 
}

飼料

@Entity(foreignKeys = arrayOf(ForeignKey(
     entity = Owner::class, 
     parentColumns = arrayOf("id"), 
     childColumns = arrayOf("owner_id") 
))) 
data class Feed(
     @ColumnInfo(name = "url") @PrimaryKey var URL: String = "", 
     @ColumnInfo(name = "copyright") var copyright: String? = null, 
     @ColumnInfo(name = "description") var description: String? = null, 
     @ColumnInfo(name = "itemGUIDs") var itemGUIDs: List<String> = emptyList(), 
     @ColumnInfo(name = "author") var author: String? = null, 
     @ColumnInfo(name = "block") var block: Boolean = false, 
     @ColumnInfo(name = "categoryIds") var categoryIds: List<Int> = emptyList(), 
     @ColumnInfo(name = "explicit") var explicit: Boolean = false, 
     @ColumnInfo(name = "image_url") var imageUrl: String? = null, 
     @ColumnInfo(name = "owner_id") var ownerId: Int = -1, 
     @ColumnInfo(name = "subtitle") var subtitle: String? = null, 
     @ColumnInfo(name = "summary") var summary: String? = null, 
     @ColumnInfo(name = "language") var language: String = "", 
     @ColumnInfo(name = "link") var link: String = "", 
     @ColumnInfo(name = "title") var title: String = "", 
     @ColumnInfo(name = "expiry") var expiry: Date = Date(), 
     @ColumnInfo(name = "subscribed") var subscribed: Boolean = false 
) : Serializable

所有者

@Entity 
data class Owner(
     @ColumnInfo(name = "name") var name: String? = null, 
     @ColumnInfo(name = "email") var email: String? = null 
) : Serializable { 
    @ColumnInfo(name = "id") 
    @PrimaryKey(autoGenerate = true) 
    var id: Int = 0 
}

來源

2017-06-25 JaySee

事實證明，使用LiveData與房間時，它立即返回，因此調用LiveData.value立即給出null，同時它異步獲取要提供給觀察者的實際數據，因此如果嘗試從非LiveData調用進行轉換，則不能用作替換的下降。這是在這裏記錄：https://developer.android.com/reference/android/arch/lifecycle/LiveData.html#getValue()

返回當前值。請注意，在後臺線程中調用此方法並不能保證會收到最新的值集。

來源

2017-06-26 01:23:48 JaySee

Android室沒有返回任何與url作爲參數

回答

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