從字符串“”到類型“ Double”的轉換無效

Question

即使在值周圍放置CType並將其定義為double時，嘗試執行此代碼時仍會收到此錯誤。

Private Sub GridView1_RowDeleting(sender As Object, e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles GridView1.RowDeleting
    ' The deletion of the individual row is automatically handled by the GridView.
    Dim dbDelete As New pbu_housingEntities
    ' Remove individual from the bed.
    Dim occupant As String = GridView1.Rows(e.RowIndex).Cells(2).Text
    Dim room As String = GridView1.Rows(e.RowIndex).Cells(5).Text
    Dim building As String = GridView1.Rows(e.RowIndex).Cells(4).Text
    Dim find_id = From p In dbDelete.Residents _
                  Where p.person_name = occupant _
                  Select p


    Dim remove_bed = From p In dbDelete.Beds _
                     Where p.occupant = find_id.FirstOrDefault.id _
                     Where p.room = room _
                     Where p.building = building _
                     Order By p.id Descending _
                     Select p
    remove_bed.First.occupant = CType(0, Double)
    dbDelete.SaveChanges()

    ' Increase number of open spaces in room.
    Dim update_occupancy = From p In dbDelete.Rooms _
                           Where p.room1 = room
                           Where p.building = building _
                           Select p

    update_occupancy.First.current_occupancy = update_occupancy.First.current_occupancy - 1
    dbDelete.SaveChanges()

End Sub

Answer 1

我懷疑問題出在這一行：

Where p.occupant = find_id.FirstOrDefault.id _

這些都是相同類型的嗎？ 我懷疑這行的原因是，在較早的另一個表中，您使用的是occupant名稱。 我將檢查您的where子句中的其他值是否也與您將它們進行比較的類型匹配。

該錯誤可能出現在分配行中的原因是，直到您對其First運行，該查詢才被執行。 該錯誤最有可能出現在查詢中，而不是分配中。

Answer 2

它不能將空字符串轉換為雙精度型。 放入if語句，檢查是否有空字符串，如果為空，則將double設置為0。