Question

这是我的代码

<WebMethod()> _
    Public Function getlocationsbypro(searchtype As String, crime As String, proid As String, startdate As String, enddate As String, starttime As String, endtime As String) As List(Of crimelocation)

    If searchtype = "withdatetime" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime And (locations.DATE_COMTD >= Convert.ToDateTime(startdate) And locations.DATE_COMTD <= Convert.ToDateTime(enddate)) _
                      And (locations.gettimecom >= starttime And locations.gettimecom <= endtime) _
                      Select locations
        Return giveloc.ToList
    ElseIf searchtype = "withdate" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime And (locations.DATE_COMTD >= Convert.ToDateTime(startdate) And locations.DATE_COMTD <= Convert.ToDateTime(enddate)) _
                      Select locations

        Return giveloc.ToList
    ElseIf searchtype = "without" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime _
                      Select locations

        Return giveloc.ToList
    End If

End Function

但是当我编译它时说该函数没有在所有代码路径上返回一个值，尽管我的所有if语句都有一个return语句我错过了什么，而且我注意到那时如果没有elseif语句只是通常如果结束它不会给我上面说的错误。

Answer 1

所有代码路径都不返回值。

 If searchtype = "withdatetime" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime And (locations.DATE_COMTD >= Convert.ToDateTime(startdate) And locations.DATE_COMTD <= Convert.ToDateTime(enddate)) _
                      And (locations.gettimecom >= starttime And locations.gettimecom <= endtime) _
                      Select locations
        Return giveloc.ToList
    ElseIf searchtype = "withdate" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime And (locations.DATE_COMTD >= Convert.ToDateTime(startdate) And locations.DATE_COMTD <= Convert.ToDateTime(enddate)) _
                      Select locations

        Return giveloc.ToList
    ElseIf searchtype = "without" Then
        Dim locs As New crimemsapslocationDataContext
        Dim giveloc = From locations In locs.crimelocations _
                      Where locations.INCIDENTTYPE = crime _
                      Select locations

        Return giveloc.ToList
    End If
 // if none of the if-else conditions are met your code goes straight to here and there is not return statement
    Return null; // this fixes it.

你也可以在if-else的末尾放一个else，这可能会更好。我没有注意到ElseIf，因为我没有写那些VB的东西。

Answer 2

在结束If后你需要另一个Return语句。否则，如果没有满足If或ElseIf条件，则代码将不返回任何内容。

LINQ函数返回列表但编译器表示函数不会在所有代码路径上返回值

2 个答案: