从字符串“”转换输入 'Double 无效

Question

尝试执行此代码时，即使在值周围放置 CType 并将其定义为 double 之后，我仍然收到此错误？

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

它无法将空字符串转换为双精度值。放入 if 语句检查是否为空字符串，如果为空则将 double 设置为 0。

Answer 2

我怀疑问题出在这一行：

Where p.occupant = find_id.FirstOrDefault.id _

这两个都是同一类型吗？我怀疑这一行的原因是因为在之前的另一个表中，您使用占用作为人名。我会检查 where 子句中的其他值是否也与您要比较的类型匹配。

错误可能出现在赋值行中的原因是，在您运行 First 之前不会执行查询。该错误很可能出现在查询中，而不是出现在分配中。