如何将带有Texbox文本的列表列相乘？ [英] How Do I Multiply A List Column With A Texbox Text?

问题描述

请帮我查一下我的评论

  private   void  addbtn_Click（ object  sender，EventArgs e）
 {
  string  connectionstring =  @  Data Source = .; Initial Catalog = SuperM; Integrated Security = True; 
 SqlConnection sqlcon =  new  SqlConnection（connectionstring）; 
 sqlcon.Open（）; 
 
 SqlCommand cm =  new  SqlCommand（ 选择ID，Item_Code，数量，库存中的商品，其中item_code =' + itemcodetxt.Text +  '，sqlcon）; 
 
 SqlDataReader reader = cm.ExecuteReader（）; 
 
 listView1.View = View.Details; 
  while （reader.Read（））
 {
  var  item =  new  ListViewItem（）; 
 item.Text = reader [  ID]。ToString（）; 
 item.SubItems.Add（reader [  item_code]。ToString（））; 
 item.SubItems.Add（quantitytxt.Text）; 
 item.SubItems.Add（reader [  price]。ToString（））; 
 
  //  请点击此处 
 item.SubItems.Add （listView1.Items [ 3 ]。ToString（）* listView1.Items [ 2 ]。ToString（） ）; 
 listView1.Items.Add（item）; 
 
 
} 
 

解决方案

通过乘法字符串你有什么期望？如果这些字符串不是有效的数字表示怎么办？



所有算术方法都必须针对数字运行，而不是字符串。



提示：

<前lang =cs> 十进制数量，价格，总数;
if （ decimal .TryParse（listView1.Items [ 3 ]。ToString（）， out 价格）&&& decimal 。 TryParse（listView1.Items [ 2 ]。ToString（）， out quantity））{
总=价格*数量;
}
其他 {
// 价格或数量存在问题，这不是有效的数字代表
}

< blockquote>尝试 item.SubItems.Add（Convert.ToInt（listView1.Items [3]）* Convert.ToInt（listView1.Items [2]））;

更简洁的方法是使用 Int32.TryParse [ ^ ]以确保列表视图列中的值是整数，

一些事情：

1.切换到使用SQL的参数化查询以避免SQL注入问题的风险：

  private   void  addbtn_Click（ object  sender，EventArgs e）
 {
  string  connectionstring =  @ 数据源= .;初始目录= SuperM;集成安全性=真; 
 SqlConnection sqlcon =  new  SqlConnection（connectionstring）; 
 sqlcon.Open（）; 
 
 SqlCommand cm =  new  SqlCommand（ 选择ID，Item_Code，数量，库存中的商品，其中item_code = @ICode，sqlcon）; 
 
 SqlParameter param = cm.Parameters.Add（  @ ICode， SqlDbType.NVarChar）; 
 param.Value = itemcodetxt.Text; 
 SqlDataReader reader = cm.ExecuteReader（）; 

2.正如其他人所说，你不能乘以字符串。这也带来了DB中数据类型的问题？我将假设价格列具有数字数据类型，如整数，单，双，货币。

  int 数量;  //  我假设这实际上是一个整数 
  if （！int.TryParse（quantitytxt.Text， out 数量））
 {
  //  输入无效，您决定如何处理这种情况！ 
} 
 < span class =code-keyword> while （reader.Read（））
 {
  var  item =  new  ListViewItem（）; 
 item.Text = reader [  ID]。ToString（）; 
 item.SubItems.Add（reader [  item_code]。ToString（））; 
 item.SubItems.Add（quantitytxt.Text）; 
  decimal  price = Convert.ToDecimal（reader [ 价格]）;  //  演员表可能已足够 
 item.SubItems.Add（price.ToString（） ）; 
 
 item.SubItems.Add（（quantity * price）.ToString（））; 
 listView1.Items.Add（item）; 
} 
 

上述代码尚未尝试过...

Please help me check where i comment

private void addbtn_Click(object sender, EventArgs e)
       {
           string connectionstring = @"Data Source=.;Initial Catalog=SuperM;Integrated Security=True";
           SqlConnection sqlcon = new SqlConnection(connectionstring);
           sqlcon.Open();

           SqlCommand cm = new SqlCommand("Select ID, Item_Code, quantity, price from stock where item_code = '" + itemcodetxt.Text + "'", sqlcon);

           SqlDataReader reader = cm.ExecuteReader();

           listView1.View = View.Details;
 while (reader.Read())
           {
               var item = new ListViewItem();
               item.Text = reader["ID"].ToString();
               item.SubItems.Add(reader["item_code"].ToString());
               item.SubItems.Add(quantitytxt.Text);
               item.SubItems.Add(reader["price"].ToString());

             //please check here
 item.SubItems.Add(listView1.Items[3].ToString() * listView1.Items[2].ToString());
               listView1.Items.Add(item);


           }

解决方案

What do you expect by multiplicating strings? What if these strings are not valid number representations.

All arithmetic methods must be run against numbers, not strings.

Tip:

decimal quantity, price, total;
if (decimal.TryParse(listView1.Items[3].ToString(), out price) && decimal.TryParse(listView1.Items[2].ToString(), out quantity)) {
   total = price * quantity;
}
else {
   // There is a problem with either the price, or the quantity, which is not a valid number representation
}

Try item.SubItems.Add(Convert.ToInt(listView1.Items[3]) * Convert.ToInt(listView1.Items[2]));
A neater way would be to use Int32.TryParse[^] to make sure that the values inside the list view columns are integers,

A couple of things:
1. Switch to using a parameterized query for the SQL to avoid the risk of SQL injection issues:

private void addbtn_Click(object sender, EventArgs e)
{
  string connectionstring = @"Data Source=.;Initial Catalog=SuperM;Integrated Security=True";
  SqlConnection sqlcon = new SqlConnection(connectionstring);
  sqlcon.Open();
 
  SqlCommand cm = new SqlCommand("Select ID, Item_Code, quantity, price from stock where item_code = @ICode", sqlcon);

  SqlParameter param = cm.Parameters.Add("@ICode", SqlDbType.NVarChar);
  param.Value = itemcodetxt.Text; 
  SqlDataReader reader = cm.ExecuteReader();

2. As others have said, you cannot multiply strings. This also brings the question of what are the data types in the DB? I'm going to assume that the price column has a numeric data type like Integer, Single, Double, Currency.

int quantity; // I'm assuming this is actually an integer
if (!int.TryParse(quantitytxt.Text, out quantity))
{
  // the input is invalid, you decide how you want to handle this case!
}
while (reader.Read())
{
  var item = new ListViewItem();
  item.Text = reader["ID"].ToString();
  item.SubItems.Add(reader["item_code"].ToString());
  item.SubItems.Add(quantitytxt.Text);
  decimal price = Convert.ToDecimal(reader["price"]); // a cast might be sufficient
  item.SubItems.Add(price.ToString());

  item.SubItems.Add((quantity * price).ToString());
  listView1.Items.Add(item);
}

The above code has not been tried...

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