.NET v4.5中的C#Substring()错误？

Question

我有点疑惑为什么Substring()函数不能正常工作.它只是不会在字符串末尾删除逗号.

见下面的示例代码......

public static string OrderByClauseBuilder(string parmSortByColumn)
{
    if (parmSortByColumn.LastIndexOf(",") > -1) { 
        parmSortByColumn.Substring(0, parmSortByColumn.LastIndexOf(","));
    }
    return parmSortByColumn;
}
protected void Page_Load(object sender, EventArgs e)
{
    string sqlAsk = "";
    string value = "stocknumber asc,";

    sqlAsk = OrderByClauseBuilder(value);
}

Answer 1

字符串在.NET中是不可变的,并且每个字符串方法都返回一个新的,经过修改的方法.因此,您必须做一些调整:

public static string OrderByClauseBuilder(string parmSortByColumn)
{
    if (parmSortByColumn.LastIndexOf(",") > -1) { 
        parmSortByColumn = parmSortByColumn.Substring(0, parmSortByColumn.LastIndexOf(","));
    }
    return parmSortByColumn;
}