Visual Basic：图片框数组的声明

Question

Why is that the code below gives a null reference exception at runtime?(assuming that the timer starts ticking when the form opens). I'm gonna use the array in many sub and I don't want to declare the array in each subs for them to work if it is possible because it makes the programs very long.

NOTE: Pictureboxes Enemy1_1, Enemy1_2, Enemy1_3 and so on are already on the form from the start.

Public Class Form1
    Dim Array1() As PictureBox = {Enemy1_1, Enemy1_2, Enemy1_3}
    Dim Array2() As PictureBox = {Enemy2_1, Enemy2_2, Enemy2_3}
    Dim Array3() As PictureBox = {Enemy3_1, Enemy3_2, Enemy3_3}

    Private Sub timer1_Tick(sender As Object, e As EventArgs) Handles timer1.Tick
        For index As Integer = 0 To 2
            Array1(index).Left += 5
            Array2(index).Left += 5
            Array3(index).Left += 5
        Next
    End Sub
End Class

Answer 1

Maybe you were looking for something more sophisticated than the below, LOL... but at least it will probably stop the page from bombing out, and/or confirm where the exception is happening:

Public Class Form1
    Dim Array1() As PictureBox = {Enemy1_1, Enemy1_2, Enemy1_3}
    Dim Array2() As PictureBox = {Enemy2_1, Enemy2_2, Enemy2_3}
    Dim Array3() As PictureBox = {Enemy3_1, Enemy3_2, Enemy3_3}

    Private Sub timer1_Tick(sender As Object, e As EventArgs) Handles timer1.Tick
        For index As Integer = 0 To 2
            If Array1(index) IsNot Nothing Then
                Array1(index).Left += 5
            End If
            If Array2(index) IsNot Nothing Then
                Array2(index).Left += 5
            End If
            If Array3(index) IsNot Nothing Then
                Array3(index).Left += 5
            End If
        Next
    End Sub
End Class