foreach(Control gb in this.Controls)
 {
       if(gb is GroupBox)
       {
          foreach(Control tb in gb.Controls)
          {
             if(tb is TextBox)
             {
                 //here is where you access all the textboxs.
             }
          }
       }
 }

但是如果您已经定义了每个TextBox名称通过循环获取每个TextBox有什么意义呢？
您可以定义一个List<TextBox>来保存每个TextBox的引用，同时创建它们，然后只需通过List来访问每个TextBox。

以下是我的建议：

foreach(var groupBox in Controls.OfType<GroupBox>())
{
    foreach(var textBox in groupBox.Controls.OfType<TextBox>())
    {
        // Do Something
    }
}

或者将其置于一个循环中：

foreach (var textBox in Controls.OfType<GroupBox>().SelectMany(groupBox => groupBox.Controls.OfType<TextBox>()))
{
    // Do Something
}

请尝试以下代码，

Control.ControlCollection coll = this.Controls;
foreach(Control c in coll) {
  if(c != null)
}

foreach (var ctrl in gbDatabaseColumns.Controls)
{
     if (ctrl is DevExpress.XtraEditors.TextEdit)
     {
        StoreTextEdit(config, (ctrl as DevExpress.XtraEditors.TextEdit));
     }
}

foreach (Control txx in groupBox2.Controls)
{
    if (txx is TextBox)
        txx.Text = "";
    if (txx is ComboBox)
        txx.Text = "";
    // if (txx is DateTimePicker)
    //     txx.Text = ""; Datetimepicker text can't be erased
}