如何使用 c# Winforms 执行字符串和整数？

Question

在我的发票表单中，我有textEdit1，它最初显示"INV001"。然后我们将该发票表单详细信息存储到 MS Access 数据库中。下次继续 textEdit1 会自动显示下一个发票编号，例如 "INV002"。如何执行此操作？

如果只是数字，我试过这个代码成功，但现在我也有 3 个字母，那么如何执行呢？

OleDbConnection con =
    new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:/Srihari/Srihari/Invoice.accdb");
con.Open();

OleDbCommand cmd =
    new OleDbCommand(
        "SELECT * FROM NewInvoice_1 WHERE InvoiceNumber = (select max(InvoiceNumber) from NewInvoice_1)",
        con);

OleDbDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
    int a = reader.GetInt32(1);
    TXE_Invoice_Number.Text = (1 + a).ToString();
}

Answer 1

我会在数据库中存储int 而不是string：

using(var con = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:/Srihari/Srihari/Invoice.accdb"))
using(var cmd = new OleDbCommand("SELECT MAX(InvoiceNumber) from NewInvoice_1", con))
{
    con.Open();
    int max = 0;
    object objMax = cmd.ExecuteScalar();
    if(objMax != null) max = (int) objMax;
    int newMax = max++; // insert this into the database instead of the string "INV001"
    // you can use newMax.ToString("000") or ToString("D3") or ToString().PadLeft(3, '0')
    string newNumber = string.Format("INV{0}", newMax.ToString().PadLeft(3, '0'));
    // ...
}

如果你坚持string和这种模式"INV001"：

string maxStr = (string)cmd.ExecuteScalar() ?? "INV0";
int newMax = int.Parse(maxStr.Substring(3)) + 1;
string newNumber = string.Format("INV{0}", newMax.ToString().PadLeft(3, '0'));

在这个Substring-aproach 中是否有前导零并不重要。

Answer 2

使用此功能，您可以从文本中提取数字 - 然后添加 1 并再次添加文本。

小心。此函数使用德国数字格式，其中逗号是小数分隔符，Point 是千位分隔符！

    public static int ConvertToIntEx(object value) {
        try {
            if (value == null) return 0;
            return Convert.ToInt32(ConvertToDecimalEx(value));
        } catch {
            return 0;
        }
    }

    /// <summary>
    /// Tryies to convert the string to a decimal (like VB val() )
    /// </summary>
    /// <param name="value"></param>
    /// <returns>null if the string does not start with a valid decimal number</returns>
    public static decimal? ConvertToDecimalEx(object value) {
        if (value == null || string.IsNullOrWhiteSpace(value.ToString())) return null;
        var ret = string.Empty;
        foreach (var c in value.ToString()) {
            if (c == ' ') continue;
            if (c == '.') continue;
            if (c == ',' || c == '-') {
                if (c == ',' && ret.Contains(",")) continue;
                if (c == '-' && ret.Contains("-")) continue;
                ret += c.ToString();
                continue;
            }
            if (!IsNumeric(c)) {
                if (ret.Length > 0) {
                    //, or slash followed by non numeric chars are ignored
                    if (ret == "," || ret == "-" || ret == ",-" || ret == "-,") {
                        ret = string.Empty;
                        continue;
                    }
                    break; //Ignore Letters in front of numbers
                }
            } else {
                ret += c.ToString();
            }
        }
        ret = ret.Trim();
        if (ret.IndexOf("-") > 0) { //Remove all Slashes not at the beginning otherwise the number would also be interpreted as minus
            ret = ret.Replace("-", "");
        }
        if (IsNumeric(ret)) {
            return ConvertToDecimal(ret);
        } else {
            return null;
        }
    }


    /// <summary>
    /// IsNumeric Function - returns true if the Expression is a valid Number or valid decimal Number
    /// </summary>
    /// <param name="expression"></param>
    /// <returns></returns>
    public static bool IsNumeric(object expression) {
        // Define variable to collect out parameter of the TryParse method. If the conversion fails, the out parameter is zero.
        double retNum;

        // The TryParse method converts a string in a specified style and culture-specific format to its double-precision floating point number equivalent.
        // The TryParse method does not generate an exception if the conversion fails. If the conversion passes, True is returned. If it does not, False is returned.
        var expressionStr = Convert.ToString(expression).Replace(".", string.Empty);
        var isNum = Double.TryParse(
            expressionStr,
            System.Globalization.NumberStyles.Any,
            System.Globalization.NumberFormatInfo.InvariantInfo,
            out retNum);

        return isNum;
    }