变量在赋值前被使用，可能导致null错误！！！！！

[haolly]

Public Class Child
    Dim arry(,) As String
    


    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim temp As Boolean = True
        If TextBox1.Text = "" Then
            MessageBox.Show("请输入姓名", "出错了!", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf IsNumeric(TextBox2.Text) = False Then
            MessageBox.Show("成绩必须为正整数", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf CInt(TextBox2.Text) > 100 Then
            MessageBox.Show("成绩不能大于100", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf IsNumeric(TextBox3.Text) = False Then
            MessageBox.Show("成绩必须为正整数", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf CInt(TextBox3.Text) > 100 Then
            MessageBox.Show("成绩不能大于100", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf IsNumeric(TextBox4.Text) = False Then
            MessageBox.Show("成绩必须为正整数", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf CInt(TextBox4.Text) > 100 Then
            MessageBox.Show("成绩不能大于100", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf IsNumeric(TextBox5.Text) = False Then
            MessageBox.Show("成绩必须为正整数", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False
        ElseIf CInt(TextBox5.Text) > 100 Then
            MessageBox.Show("成绩不能大于100", "出错了", MessageBoxButtons.OK, MessageBoxIcon.Error)
            temp = False

        End If
        If temp = True Then
            Dim fmtstr As String = "{0,-24}{1,-5}{2,-5}{3,-5}{4,-6}{5,-7}{6,-5}"
            Dim sum As Double = CDbl(TextBox2.Text) + CDbl(TextBox3.Text) + CDbl(TextBox4.Text) + CDbl(TextBox5.Text)
            Dim avg As Double = sum / 4
            Dim gread As String

            If 0 <= avg < 60 Then

                gread = "E"
            ElseIf 60 <= avg < 70 Then


                gread = "D"
            ElseIf 70 <= avg < 80 Then
                gread = "C"
            ElseIf 80 <= avg < 90 Then

                gread = "B"
            ElseIf 90 <= avg <= 100 Then
                gread = "A"


            End If
            Dim i As Integer
            ReDim Preserve arry(i, 6)


            arry(i, 0) = TextBox1.Text
            arry(i, 1) = TextBox2.Text
            arry(i, 2) = TextBox3.Text
            arry(i, 3) = TextBox4.Text
            arry(i, 4) = TextBox5.Text
            arry(i, 5) = avg
            arry(i, 6) = gread







            Form1.ListBox1.Items.Add(String.Format(fmtstr, arry(i, 0), arry(i, 1), arry(i, 2), arry(i, 3), arry(i, 4), arry(i, 5), arry(i, 6)))

            MessageBox.Show("已添加到列表中,请注意保存", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information)

            TextBox1.Clear()
            TextBox2.Clear()
            TextBox3.Clear()
            TextBox4.Clear()
            TextBox5.Clear()
            i += 1
        End If






    End Sub

End Class

就那个gread有问题了。

[herocxgood]

我看是那個 Dim i As Integer出了問題，沒有初始化，后面的arry(i, 0) = TextBox1.Text就用到了i

[haolly]

楼上，你在仔细看看，不是i的问题呀，是gread的问题

[haolly]

Me.ListBox1.Items.Add(String.Format(fmtstr, Child.arry(i, 0), Child.arry(i, 1), Child.arry(i, 2), Child.arry(i, 3), Child.arry(i, 4), Child.arry(i, 5), Child.arry(i, 6)))
我在另一个窗口引用时出现错误，“未将对象引用设置到对象的实例。”
可是我明明在窗口中已经赋值了呀
arry(i, 0) = TextBox1.Text
arry(i, 1) = TextBox2.Text
arry(i, 2) = TextBox3.Text
arry(i, 3) = TextBox4.Text
arry(i, 4) = TextBox5.Text
arry(i, 5) = avg
arry(i, 6) = gread

[herocxgood]

LZ說gread出了問題
Dim gread As String

If 0 <= avg < 60 Then

gread = "E"
ElseIf 60 <= avg < 70 Then


gread = "D"
ElseIf 70 <= avg < 80 Then
gread = "C"
ElseIf 80 <= avg < 90 Then

gread = "B"
ElseIf 90 <= avg <= 100 Then
gread = "A"
這里給gread賦值我看也沒啥問題啊
LZ可以試著將賦值后的gread打印出來看看是否為A,B,C，D,E中的一個值

[yanlongwuhui]

Dim gread As String=""试试

[chinaboyzyq]

If 0 <= avg < 60 Then
gread = "E"
ElseIf 60 <= avg < 70 Then
.
.

if avg>=0 and avg<60 then
gread="E"
elseif avg>=60 and avg<70 then
.
.
另外，使用变量尽量先定义变量。

[xiansr]

ReDim Preserve arry(i, 6)

改为 7 试试