' 安全遍历所有数据行（不包括新行）
For i As Integer = 0 To DataGridView1.Rows.Count - 1
    ' 检查是否是新建行（非数据行）
    If Not DataGridView1.Rows(i).IsNewRow Then
        ' 处理每一行数据
        Dim cellValue As String = DataGridView1.Rows(i).Cells(0).Value.ToString()
        ' 其他操作...
    End If
Next

' 或者使用For Each循环（推荐）
For Each row As DataGridViewRow In DataGridView1.Rows
    If Not row.IsNewRow Then
        ' 处理每一行数据
        Dim cellValue As String = row.Cells(0).Value.ToString()
        ' 其他操作...
    End If
Next

' 确保有行存在再循环
If DataGridView1.Rows.Count > 0 Then
    For i As Integer = 0 To DataGridView1.Rows.Count - 1
        ' 处理代码
    Next
End If

For Each row As DataGridViewRow In DataGridView1.Rows
    If Not row.IsNewRow Then
        For Each cell As DataGridViewCell In row.Cells
            ' 检查单元格是否有值
            If cell.Value IsNot Nothing Then
                ' 处理单元格值
            End If
        Next
    End If
Next