问题遇到的现象和发生背景
vb.net的变量‘sqlcmd’在赋值前被使用,可能会在运行时导致null引用异常
问题相关代码，请勿粘贴截图
Public Class FrmLInfoEdit
Private Sub SetHeadTitle()
'设置每列标题
dGridL.Columns(0).HeaderText = "住户号"
dGridL.Columns(1).HeaderText = "姓名"
dGridL.Columns(2).HeaderText = "性别"
dGridL.Columns(3).HeaderText = "年龄"
dGridL.Columns(4).HeaderText = "籍贯"
dGridL.Columns(5).HeaderText = "民族"
dGridL.Columns(6).HeaderText = "出租人"
dGridL.Columns(7).HeaderText = "房屋号"
dGridL.Columns(8).HeaderText = "入住日期"
dGridL.ColumnHeadersHeight = 28
Dim i As Integer
For i = 0 To 8
dGridL.Columns(i).Width = 90
Next i
dGridL.Columns(11).Width = 0
End Sub
Private Sub frmLInfoEdit_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim da As SqlClient.SqlDataAdapter = Nothing
Dim dt As DataTable
dt = SQLQRY("SELECT*FROM Resident", da)
dGrdL.DataSource = dt
SetHeadTitle()
End Sub
Private Sub cmdFind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdFind.Click
Dim sqlcmd As String
If Not "OptLNo" And Not "OptLName" And Not "OptAll" Then
MsgBox("请输入要查询的方式!", vbOKOnly, "提示")
Exit Sub
End If
If "OptLNo" Then
If txtLNo.Text = "" Then
MsgBox("请输入住房号!", vbOKOnly, "提示")
Exit Sub
End If
sqlcmd = "SELECT*FROM Resident WHERE Resident_ID=""&txtLNo.Text&"""
End If
If "OptLName" Then
If txtLName.Text = "" Then MsgBox("请输入姓名!", vbOKOnly, "提示")
Exit Sub
End If
If sqlcmd = "SELECT*FROM Resident WHERE Name=""&txtLName.Text&""" Then
End If
If "OptAll" Then sqlcmd = "SELECT*FROM Resident"
Dim da As SqlClient.SqlDataAdapter = New SqlClient.SqlDataAdapter()
Dim dt As DataTable = New DataTable()
dt = SQLQRY(sqlcmd, da)
If dt.Rows.Count = 0 Then MsgBox("查无结果!", vbOKOnly, "提示")
Exit Sub
dGrdL.DataSource = dt
SetHeadTitle()
End Sub
Private Sub cmdEdit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdEdit.Click
Dim sqlcmd As String
Dim dt As DataTable
Dim Resident_Id As String
Resident_Id = dGrdL.CurrentRow.Cell("Resident_Id").Values.ToString()
If String.IsNullOrEmpty(Resident_Id) Then
MsgBox("没有被选择的记录!", vbOKOnly, "提示")
Exit Sub
End If
sqlcmd = "SELECT*FROM Resident WHERE Resident_ID=""&ResidenID&"""
dt = SQLQRY(sqlcmd, Nothing)
If dt.Rows.Count = 0 Then
MsgBox("找不到住户资料!", vbOKOnly, "提示")
Exit Sub
End If
If dt.Rows(0).Item("Leave_Time") & "" <> "" Then
MsgBox("住户已经退租了!", vbOKOnly, "提示")
Exit Sub
End If
frmLInfoRecord.Text = "住户住房信息修改"
frmLInfoRecord.txtAdNum.Text =
frmLInfoRecord.txtName.Text =
frmLInfoRecord.txtAge.Text = dt.Rows(0).Item("Age")
frmLInfoRecord.CboSex.Text = dt.Rows(0).Item("Sex")
frmLInfoRecord.txtOrigin.Text = dt.Rows(0).Item("Native_Place")
frmLInfoRecord.txtVolk.Text = dt.Rows(0).Item("Nation")
frmLInfoRecord.txtHouseNo.Text = dt.Rows(0).Item("House_No")
frmLInfoRecord.txtCboDate.Text = dt.Rows(0).Item("InCome_Time")
frmLInfoRecord.ShowDialog()
End Sub
Private Function SQLQRY(ByVal p1 As String, ByVal da As SqlClient.SqlDataAdapter) As DataTable
Throw New NotImplementedException
End Function
Private Function dGrdL() As Object
Throw New NotImplementedException
End Function
Private Function dt() As Object
Throw New NotImplementedException
End Function
Private Sub OptAll_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OptAll.CheckedChanged
End Sub
Private Sub cmdDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdDelete.Click
Dim Resident_ID As String
Dim sqlcmd As String
Resident_ID = dGrdL.CurrentRow.Cells("Resident_ID").Values.ToString()
If String.IsNullOrEmpty(Resident_ID) Then
MsgBox("没有被选择的记录!", vbOKOnly, "提示")
Exit Sub
End If
If MsgBox("是否确定实需要删除该住户档案?", vbYesNo + vbQuestion + vbDefaultButton2, "提示") = vbYes Then
sqlcmd = "Delete From Resident Where Resident_ID=""&ResidentID&"""
SQLDML(sqlcmd)
MsgBox("已删除该记录!", vbOKOnly, "提示")
frmLInfoEdit_Load(Me, New EventArgs())
End If
End Sub
Private Sub cmdExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdExit.Click
Me.Close()
Me.Dispose()
End Sub
End Class
运行结果及报错内容
求指点，再次感谢！
