如何在 VB 的 运行 时间创建文本框时停止 'Object reference not set to an instance of an object'

Question

对于一个项目，我需要在 运行 时创建文本框，为此我使用了这段代码；

Dim AOP As Integer = GlobalVariables.AOP
Dim tb(11, 11) As TextBox
Dim LocationX As Integer
Dim LocationY As Integer
Dim count As Integer = 2

LocationX = 10
LocationY = 10
tb(1, 0).Name = "txtRoot"
tb(1, 0).Size = New Size(170, 20)
tb(1, 0).Location = New Point(LocationX, LocationY)
tb(1, 0).Visible = False

然后我可以使用这个 For 循环循环它；

For i = 1 To AOP
        If count > AOP Then

        Else
            If i = AOP Then
                LocationY = LocationY + 10
                LocationX = 10
                tb(count, 0).Name = "txtXValue" & 0 & "YValue" & count
                tb(count, 0).Size = New Size(170, 20)
                tb(count, 0).Location = New Point(LocationX, LocationY)
                Controls.Add(tb(count, 0))
                count = count + 1
                i = 1
            Else
                LocationX = LocationX + 10
                tb(count, i).Name = "txtXValue" & i & "YValue" & count
                tb(count, i).Size = New Size(170, 20)
                tb(count, i).Location = New Point(LocationX, LocationY)
                Controls.Add(tb(count, i))
            End If
        End If
Next

这在理论上是可行的，但是，当代码到达该行时；

tb(1, 0).Name = "txtRoot"

它returns错误'Object reference not set to an instance of an object' 我想知道这周围是否有任何东西？或者如果这种创建文本框的方式不可行？任何帮助将不胜感激。

Answer 1

您已初始化数组但未添加初始化TextBoxes，该数组目前仅包含Nothing。另请注意，数组是从零开始的，因此第一个 TextBox 在 tb(0, 0).

中

For i As Int32 = 0 To tb.GetLength(0) - 1
    For ii As Int32 = 0 To tb.GetLength(1) - 1
        tb(i, ii) = New TextBox()
        tb(i, ii).Visible = False
        ' .... '
    Next
Next

现在都初始化好了。