如何從MySQL查詢數據存儲在變量中

Question

當我執行查詢我想獲得的將被存儲在一個變量的結果（a）和然後我想該變量將被轉換成int並乘以的另一個的值文本框（textbox1），並將其存儲在另一個文本框（textbox2）中。 繼承人的整個形式

private void menustart_Load(object sender, EventArgs e) 
    { 
     // TODO: This line of code loads data into the 'cmsDataSet.menulist' table. You can move, or remove it, as needed. 



     String con = "datasource = localhost; port=3306;username=root;password=brianfdes93"; 
     MySqlConnection mycon = new MySqlConnection(con); 

     //wine 
     string qw = "select wine from cms.menulist"; 
     MySqlDataAdapter da = new MySqlDataAdapter(qw, mycon); 
     DataTable dt1 = new DataTable(); 
     da.Fill(dt1); 
     foreach (DataRow row in dt1.Rows) 
     { 
      string wine = string.Format("{0}", row.ItemArray[0]); 
      comboBox1.Items.Add(wine); 
     } 

     //nvstarter 
     string qsnv = "select st_nonveg from cms.menulist"; 
     MySqlDataAdapter da1 = new MySqlDataAdapter(qsnv, mycon); 
     DataTable dt2 = new DataTable(); 
     da1.Fill(dt2); 
     foreach (DataRow row in dt2.Rows) 
     { 
      string nvs = string.Format("{0}", row.ItemArray[0]); 
      comboBox2.Items.Add(nvs); 
     } 

     //vstarter 
     string qsv = "select st_veg from cms.menulist"; 
     MySqlDataAdapter da3 = new MySqlDataAdapter(qsv, mycon); 
     DataTable dt3 = new DataTable(); 
     da3.Fill(dt3); 
     foreach (DataRow row in dt3.Rows) 
     { 
      string vs = string.Format("{0}", row.ItemArray[0]); 
      comboBox3.Items.Add(vs); 
     } 

     //rice n v 
     string qrnv = "select rice_nonveg from cms.menulist"; 
     MySqlDataAdapter da4 = new MySqlDataAdapter(qrnv, mycon); 
     DataTable dtrnv = new DataTable(); 
     da4.Fill(dtrnv); 
     foreach (DataRow row in dtrnv.Rows) 
     { 
      string rnv = string.Format("{0}", row.ItemArray[0]); 
      comboBox4.Items.Add(rnv); 
     } 

     // rice v 
     string qrv = "select rice_veg from cms.menulist"; 
     MySqlDataAdapter da4i = new MySqlDataAdapter(qrv, mycon); 
     DataTable dtrv = new DataTable(); 
     da4i.Fill(dtrv); 
     foreach (DataRow row in dtrv.Rows) 
     { 
      string rv = string.Format("{0}", row.ItemArray[0]); 
      comboBox4i.Items.Add(rv); 
     } 



     //nvgravy 
     string qgnv = "select g_nonveg from cms.menulist"; 
     MySqlDataAdapter da5 = new MySqlDataAdapter(qgnv, mycon); 
     DataTable dtgnv = new DataTable(); 
     da5.Fill(dtgnv); 
     foreach (DataRow row in dtgnv.Rows) 
     { 
      string gnv = string.Format("{0}", row.ItemArray[0]); 
      comboBox5.Items.Add(gnv); 
     } 

     //vgravy 
     string qgv = "select g_veg from cms.menulist"; 
     MySqlDataAdapter da6 = new MySqlDataAdapter(qgv, mycon); 
     DataTable dtgv = new DataTable(); 
     da6.Fill(dtgv); 
     foreach (DataRow row in dtgv.Rows) 
     { 
      string gv = string.Format("{0}", row.ItemArray[0]); 
      comboBox6.Items.Add(gv); 
     } 

     //sanv 
     string qsanv = "select s_nonveg from cms.menulist"; 
     MySqlDataAdapter da7 = new MySqlDataAdapter(qsanv, mycon); 
     DataTable dtsanv = new DataTable(); 
     da7.Fill(dtsanv); 
     foreach (DataRow row in dtsanv.Rows) 
     { 
      string sanv = string.Format("{0}", row.ItemArray[0]); 
      comboBox7.Items.Add(sanv); 
     } 

     //sav 
     string qsav = "select s_veg from cms.menulist"; 
     MySqlDataAdapter da8 = new MySqlDataAdapter(qsav, mycon); 
     DataTable dtsav = new DataTable(); 
     da8.Fill(dtsav); 
     foreach (DataRow row in dtsav.Rows) 
     { 
      string sav = string.Format("{0}", row.ItemArray[0]); 
      comboBox8.Items.Add(sav); 
     } 
     //dessert 
     string qd = "select dessert from cms.menulist"; 
     MySqlDataAdapter da9 = new MySqlDataAdapter(qd, mycon); 
     DataTable dtd = new DataTable(); 
     da9.Fill(dtd); 
     foreach (DataRow row in dtd.Rows) 
     { 
      string sav = string.Format("{0}", row.ItemArray[0]); 
      comboBox9.Items.Add(sav); 
     } 



     mycon.Close(); 

     // to populate iod 

     int nxtorder; 

     String coni = "datasource = localhost; port=3306;username=root;password=brianfdes93"; 
     MySqlConnection myconi = new MySqlConnection(coni); 
     string query = "select MAX(o_id) from cms.order"; 
     MySqlCommand o = new MySqlCommand(query, myconi); 
     myconi.Open(); 

     MySqlDataReader reader = o.ExecuteReader(); 
     while (reader.Read()) 
     { 
      if (reader.IsDBNull(reader.GetOrdinal("max(o_id)"))) 
      { 
       nxtorder = 1; 
       tid.Text = Convert.ToString(nxtorder); 
      } 
      else 
      { 
       nxtorder = Convert.ToInt32(reader["max(o_id)"]); 
       tid.Text = Convert.ToString(nxtorder); 
      } 



     } 





     //to fill guest txtbox 




    } 

    private void button1_Click(object sender, EventArgs e) 
    { 
     starting s = new starting(); 
     s.Show(); 
     this.Close(); 
    } 





    private void button2_Click(object sender, EventArgs e) 
    { 

      tabControl1.SelectedTab = tabPage3; 
      t1.Text = t11.Text; 
      t2.Text = t12.Text; 
      t3.Text = t13.Text; 
      t4.Text = t14.Text; 
      t4i.Text = t14i.Text; 
      t5.Text = t15.Text; 
      t6.Text = t16.Text; 
      t7.Text = t17.Text; 
      t8.Text = t18.Text; 
      t9.Text = t19.Text; 
      textBox1.Text = label49.Text; 

    } 

    private void comboBox1_SelectionChangeCommitted(object sender, EventArgs e) 
    { 

     string c1 = comboBox1.SelectedItem.ToString(); 
     t1.Text = t1.Text +c1+","; 
    } 

    private void comboBox2_SelectionChangeCommitted_1(object sender, EventArgs e) 
    { 
     string c2 = comboBox2.SelectedItem.ToString(); 
     t2.Text = t2.Text + c2 + ","; 
    } 

    private void comboBox3_SelectionChangeCommitted_1(object sender, EventArgs e) 
    { 
     string c3 = comboBox3.SelectedItem.ToString(); 
     t3.Text = t3.Text + c3 + ","; 
    } 

    private void comboBox4_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c4 = comboBox4.SelectedItem.ToString(); 
     t4.Text = t4.Text + c4 + ","; 
    } 
    private void comboBox4i_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c4i = comboBox4.SelectedItem.ToString(); 
     t4i.Text = t4i.Text + c4i + ","; 
    } 
    private void comboBox5_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c5 = comboBox5.SelectedItem.ToString(); 
     t5.Text = t5.Text + c5 + ","; 
    } 

    private void comboBox6_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c6 = comboBox6.SelectedItem.ToString(); 
     t6.Text = t6.Text + c6 + ","; 
    } 

    private void comboBox7_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c7 = comboBox7.SelectedItem.ToString(); 
     t7.Text = t7.Text + c7 + ","; 
    } 

    private void comboBox8_SelectedIndexChanged(object sender, EventArgs e) 
    { 
     string c8 = comboBox8.SelectedItem.ToString(); 
     t8.Text = t8.Text + c8 + ","; 
    } 

    private void comboBox9_SelectionChangeCommitted_1(object sender, EventArgs e) 
    { 
     string c9 = comboBox9.SelectedItem.ToString(); 
     t9.Text = t9.Text + c9 + ","; 
    } 

    private void button1_Click_1(object sender, EventArgs e) 
    { 
     tabControl1.SelectedTab = tabPage3; 
     t1.Text = t21.Text; 
     t2.Text = t22.Text; 
     t3.Text = t23.Text; 
     t4.Text = t24.Text; 
     t4i.Text = t24i.Text; 
     t5.Text = t25.Text; 
     t6.Text = t26.Text; 
     t7.Text = t27.Text; 
     t8.Text = t28.Text; 
     t9.Text = t29.Text; 
     textBox1.Text = label47.Text; 
    } 



    private void button3_Click(object sender, EventArgs e) 
    { 

     if (t1.Text != "" && t2.Text != "" && t3.Text != "" && t4.Text != "" && t5.Text != "" && t6.Text != "" && t7.Text != "" && t8.Text != "" && t9.Text != "") 
     { 
     try 
     { 
      String con = "datasource = localhost; port=3306;username=root;password=brianfdes93"; 
      MySqlConnection mycon = new MySqlConnection(con); 
      string query = "insert into cms.menu(o_id,wine,st_nonveg,st_veg,rice_nonveg,rice_veg,g_nonveg,g_veg,s_veg,s_nonveg,dessert) values('" + this.tid.Text + "','" + this.t1.Text + "','" + this.t2.Text + "','" + this.t3.Text + "','" + this.t4.Text + "','" + this.t4i.Text + "','" + this.t5.Text + "','" + this.t6.Text + "','" + this.t7.Text + "','" + this.t8.Text + "','" + this.t9.Text + "')"; 
      MySqlCommand orderinsert = new MySqlCommand(query, mycon); 
      MySqlDataReader reader; 
      mycon.Open(); 
      reader = orderinsert.ExecuteReader(); 
      while (reader.Read()) 
      { 
      } 

     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message); 
     } 


     try 
     { 
      String con1 = "datasource = localhost; port=3306;username=root;password=brianfdes93"; 
      MySqlConnection mycon1 = new MySqlConnection(con1); 
      string query1 = "insert into cms.order(price_per_plate,total_amount) values('" + this.textBox1.Text + "','" + this.textBox2.Text+ "')"; 
      MySqlCommand orderinsert1 = new MySqlCommand(query1, mycon1); 
      MySqlDataReader reader; 
      mycon1.Open(); 
      reader = orderinsert1.ExecuteReader(); 
      while (reader.Read()) 
      { 
      } 
      MessageBox.Show("MENU PREFERENCE SAVED"); 
     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message); 
     } 







     } 
     else 
     { 
      MessageBox.Show("please complete the form before submitting"); 
     } 

     payment p = new payment(); 
     this.Hide(); 
     p.Show(); 
    } 

    private void tabPage3_Enter(object sender, EventArgs e) 
    { 
     String con2 = "datasource = localhost; port=3306;username=root;password=brianfdes93"; 
     MySqlConnection mycon2 = new MySqlConnection(con2); 
     string query2 = "select guest from cms.order where o_id='" + tid.Text + "'"; 
     MySqlCommand orderinsert = new MySqlCommand(query2, mycon2); 
     string a = "1"; 
     mycon2.Open(); 
     // a = orderinsert.ExecuteScalar().ToString(); 
     MySqlDataReader dr = orderinsert.ExecuteReader(); 
     while (dr.Read()) 
     { 
      a = dr.GetString(0); 

     } 
     string s = textBox1.Text; 
     int a1 = Convert.ToInt16(a); 
     int a2 = Convert.ToInt32(string.IsNullOrEmpty(textBox1.Text)); 
     textBox2.Text = Convert.ToString(a1 * a2); 
     mycon2.Close(); 
    } 
} 

}

的代碼我得到以下錯誤

輸入字符串的不正確的格式

我得到上述錯誤爲A2。

我該如何解決？ 有沒有其他方法？

Answer 1

Convert.ToInt16()用於爲給定值轉換成短（INT16）不是int（INT32）。雖然它們是整數，但短值應分配給short（int16），而不是int（int32）。您需要使用Convert.ToInt32()方法將該值轉換爲整數。

試試這個：如果textBox1.Text是空的拋出

int a2 = Convert.ToInt32(textBox1.Text); 

Answer 2

此錯誤。 使用String.IsNullOrEmpty（textBox1.Text）檢查textBox1.Text在將其轉換爲int16或int 32之前是否爲null或空。如果它爲null，那麼問題出在文本框本身。

Answer 3

替換：

int a2 = Convert.ToInt32(string.IsNullOrEmpty(textBox1.Text)); 

有：

try 
{ 
    int a2 = Int.Parse(textBox1.Text); 
} 
catch (Exception ex) 
{ 
    Console.WriteLine("Failed to parse to int! " + ex.Message); 
} 

string.IsNullOrEmpty總是返回一個布爾值。