为什么targetpoint值为0

问题是：

1 – 为什么当我想在查询行中使用值TargetPoint ，它总是返回0。

2 – 我有一个表单（比如说表单1），用户选择一些信息，并获得一些其他信息并以相同的forms（表单1）插入，用户将被引导到另一个表单来回答一些问题并返回再问一下1.问题是当用户回到表单时，这些信息被删除，他需要再次插入这些信息。

任何帮助都会很棒。

  namespace LLL { public partial class LearnerForm : Form { public string TargetPoint; private OleDbConnection connection = new OleDbConnection(); public LearnerForm() { InitializeComponent(); connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\ds.accdb"; lbl_welcome.Text = "Welcome " +Login.name +"!"; txtbox_startsubject.Text = diagnostic_evaluation.startpoint; } private void label1_Click(object sender, EventArgs e) { //MessageBox.Show("Welcome" + txtbox_user.Text); } private void button1_Click(object sender, EventArgs e) { Application.Exit(); } //static string TargetPoint = null; public void btn_start_Click(object sender, EventArgs e) { this.Hide(); diagnostic_evaluation F1 = new diagnostic_evaluation(); F1.Show(); //string TargetPoint = null; if (checkBox1.Checked) { TargetPoint = "A"; } if (checkBox2.Checked) { TargetPoint = "B"; } if (checkBox3.Checked) { TargetPoint = "C"; } if (checkBox4.Checked) { TargetPoint = "D"; } if (checkBox5.Checked) { TargetPoint = "E"; } if (checkBox6.Checked) { TargetPoint = "F"; } if (checkBox7.Checked) { TargetPoint = "G"; } if (checkBox8.Checked) { TargetPoint = "H"; } if (checkBox9.Checked) { TargetPoint = "I"; } if (checkBox10.Checked) { TargetPoint = "J"; } } private void btn_recom_Click(object sender, EventArgs e) { DataTable InteractionData = new DataTable(); connection.Open(); OleDbCommand command = new OleDbCommand(); command.Connection = connection; command.CommandText = "SELECT * FROM MainData WHERE ID IN (SELECT T1.ID FROM MainData AS T1 INNER JOIN MainData AS T2 ON T1.ID = T2.ID WHERE (T1.Lesson='" + txtbox_startsubject.Text + "' AND T2.Lesson='"+TargetPoint+"') GROUP BY T1.ID)"; OleDbDataAdapter maindata = new OleDbDataAdapter(command); DataTable interaction = new DataTable(); DataTable recommendation = new DataTable(); maindata.Fill(interaction); dataGridView1.DataSource = interaction; connection.Close(); } } }