C#错误:输入字符串的格式不正确 [英] C# error : Input string was not in a correct format

问题描述

我收到此错误:输入字符串的格式不正确."

I was getting this error: "Input string was not in a correct format."

这是我的代码:

    private void UpdatePOdetailBalance(int Qty)
    {
        int newbal;

        SqlCommand com = new SqlCommand();

        com.Connection = cn;

        newbal = Convert.ToInt16(txtQtyOrdered.Text) - Qty;
        com.CommandText =
            "UPDATE PODetail SET BalanceQty="+ newbal +" WHERE OrderID=" +
             Convert.ToInt16(txtPONumber.Text) + "AND ItemID=" +
             Convert.ToInt16(txtItemNo.Text);


        com.ExecuteNonQuery();

    }

    private void btnOK_Click(object sender, EventArgs e)
    {

            UpdatePOdetailBalance(Convert.ToInt16(txtQuantity.Text));

    }

我想计算等于txtQtyOrdered减去数量的newbal，但是我遇到此错误，请对此提供帮助.谢谢.

I want to compute the newbal which is equal to txtQtyOrdered minus Qty but i'm getting this error please help me with this. Thanks.

推荐答案

您的错误消息指出的问题可能在试图将文本框中的值转换为短整数的一行上.如果不进行任何检查，则用户键入的值可以是数字以外的任何值，并且会收到此错误消息(例如，如果用户将文本框留为空白).

The problem stated by your error message is probably on one of the lines that try to convert the value in the textboxes to a short integer. Without any check, the value typed by your user could be anything but a number and you get this error message (for example, if you user leaves the textboxes empty).

您应该尝试使用 TryParse ，然后尝试执行查询

You should try to check if the textboxes content could be converted to a valid short integer using TryParse before attempting to execute the query

int ordered;
if(!int16.TryParse(txtQtyOrdered.Text, out ordered))
{
    MessageBox.Show("Invalid number for Ordered quantity");
    return;
}
int orderID;
if(!int16.TryParse(txtPONumber.Text, out orderID))
{
    MessageBox.Show("Invalid number for OrderId");
    return;
}
int itemID;
if(!int16.TryParse(txtItemNo.Text, out itemID))
{
    MessageBox.Show("Invalid number for ItemID");
    return;
}

此时，您可以使用转换后的短整数执行计算，然后以这种方式编写查询(在AND之前添加一个空格)

At this point you could execute your calculation using the converted short integers and then write your query in this way (adding a space before the AND)

  com.CommandText =
        "UPDATE PODetail SET BalanceQty="+ newbal.ToString() +
        " WHERE OrderID=" + orderID.ToString() + 
        " AND ItemID=" + itemID.ToString();

但是，绝不建议将查询文本和用户输入的字符串串联作为一种好习惯(在您的情况下，这是无害的，因为如果转换成功，则不必担心Sql Injection，但是不必养成这种习惯去做).
因此，编写此查询的理想方法是使用参数化查询

But the string concatenation of query text and user input is never advised as a good practice (in your case is harmless because if the conversion is successful you don't have to worry about Sql Injection, but don't take the habit to do it).
So the perfect way to write this query is through the use of a parametrized query

  com.CommandText =
        "UPDATE PODetail SET BalanceQty=@newbal " +
        " WHERE OrderID=@orderID " + 
        " AND ItemID= @itemID"

  com.Parameters.AddWithValue("@newbal", newBal);
  com.Parameters.AddWithValue("@orderID", orderID);
  com.Parameters.AddWithValue("@itemID", itemID);
  com.ExecuteNonQuery();

作为一篇关于参数化查询以及为什么要使用它们的好文章，我建议

As a good article on Parameterized query and why to use them, I suggest to read these old words from Jeff Atwood

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