我正在使用 C# 创建一个 ASP.NET 应用程序，每次我尝试使用 SqlCommand 执行 SQL INSERT 时，该命令都会执行两次。我实现了这篇文章 ( SQL Insert query is executed twice ) 中的内容，但它仍然无济于事。
代码如下:
protected void btn_Add_Click(object sender, EventArgs e)
{
error.InnerHtml = " ";
SqlConnection MyConn = new SqlConnection("Data Source=.\\SQLEXPRESS;"
+ "Initial Catalog=SIMON;"
+ "Persist Security Info=True;"
+ "User ID=username;Password=password");
string sqlStatement = @"INSERT INTO [Network_Equipment] "
+ "([Network_Equipment_Name], [Network_Equipment_Type_ID], [IP_Address], [FQDN], [NetBIOS_Name], [Building_ID], [Description])"
+ " VALUES "
+ "(@Network_Equipment_Name, @Network_Equipment_Type_ID, @IP_Address, @FQDN, @NetBIOS_Name, @Building_ID, @Description)";
SqlCommand sqlCmd = new SqlCommand(sqlStatement, MyConn);
sqlCmd.Connection = MyConn;
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Name", ((in_Add_Equipment.Value == null) ? (object)DBNull.Value : (object)in_Add_Equipment.Value));
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Type_ID", ((ddl_Equipment_Type.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Equipment_Type.SelectedValue));
sqlCmd.Parameters.AddWithValue("@IP_Address", ((in_IP_Address.Value == null) ? (object)DBNull.Value : (object)in_IP_Address.Value));
sqlCmd.Parameters.AddWithValue("@FQDN", ((in_FQDN.Value == null) ? (object)DBNull.Value : (object)in_FQDN.Value));
sqlCmd.Parameters.AddWithValue("@NetBIOS_Name", ((in_NetBIOS.Value == null) ? (object)DBNull.Value : (object)in_NetBIOS.Value));
sqlCmd.Parameters.AddWithValue("@Building_ID", ((ddl_Building.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Building.SelectedValue));
sqlCmd.Parameters.AddWithValue("@Description", ((ta_Description.Value == null) ? (object)DBNull.Value : (object)ta_Description.Value));
try
{
MyConn.Open();
}
catch (Exception er)
{
error.InnerHtml = er.ToString();
return;
}
try
{
sqlCmd.ExecuteNonQuery();
}
catch (Exception er)
{
error.InnerHtml = er.ToString();
return;
}
error.InnerHtml = "Successfully added: " + in_Add_Equipment.Value;
sqlCmd.Dispose();
sqlCmd = null;
MyConn.Close();
in_Add_Equipment.Value = "";
ddl_Equipment_Type.SelectedIndex = 0;
in_IP_Address.Value = "";
in_FQDN.Value = "";
in_NetBIOS.Value = "";
ddl_Building.SelectedIndex = 0;
ta_Description.Value = "";
GridView1.DataBind();
}
我已经在 Debug模式下运行它并且 sqlCmd.ExecuteNonQuery() 只被调用一次，但我添加了两个相同的条目。
我错过了什么和/或做错了什么？
-------- 编辑 --------
我使用了 john ryan 的修改版本的代码，但还是添加了两次。
这里是所有的代码:
设备.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Equipment.aspx.cs" Inherits="SIMON.Equipment" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script language="javascript" type="text/javascript">
// disables the button specified and sets its style to a disabled "look".
function disableButtonOnClick(oButton, sButtonText, sCssClass) {
oButton.disabled = true; // set button to disabled so you can't click on it.
oButton.value = sButtonText; // change the text of the button.
oButton.setAttribute('className', sCssClass); // IE uses className for the css property.
oButton.setAttribute('class', sCssClass); // Firefox, Safari use class for the css property. (doesn't hurt to do both).
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel2" runat="server">
<ContentTemplate>
<div id="error" runat="server"> </div>
<div>
<fieldset style="display: inline-block; padding: 5px; -moz-border-radius: 8px; border-radius: 8px;">
<legend style="text-decoration: underline;">[ Add Equipment ]</legend>
<table cellpadding="3px" style="border: 0px; width: 300px;">
<tbody>
<tr>
<td style="text-align: left;"><label for="in_Add_Equipment" style="white-space: nowrap;">Equipment Name</label></td>
<td style="text-align: right;"><input id="in_Add_Equipment" runat="server" size="20" /></td>
<td style="text-align: left;"><label for="ddl_Equipment_Type" style="white-space: nowrap;">Equipment Type</label></td>
<td style="text-align: right;">
<asp:DropDownList ID="ddl_Equipment_Type"
runat="server" DataSourceID="Network_Equipment_Type" DataTextField="Network_Equipment_Type"
DataValueField="Network_Equipment_Type_ID"></asp:DropDownList>
</td>
</tr>
<tr>
<td style="text-align: left;"><label for="in_IP_Address" style="white-space: nowrap;">IP Address</label></td>
<td style="text-align: right;"><input id="in_IP_Address" runat="server" size="20" class="OnlyNumeric" /></td>
<td style="text-align: left;"><label for="in_FQDN" title="Fully Qualified Domain Name" style="white-space: nowrap;">FQDN</label></td>
<td style="text-align: right;"><input id="in_FQDN" runat="server" size="20" /></td>
</tr>
<tr>
<td style="text-align: left;"><label for="in_NetBIOS" style="white-space: nowrap;">NetBIOS Name</label></td>
<td style="text-align: right;"><input id="in_NetBIOS" runat="server" size="20" /></td>
<td style="text-align: left;"><label for="ddl_Building" style="white-space: nowrap;">Building</label></td>
<td style="text-align: right;">
<asp:DropDownList ID="ddl_Building" runat="server"
DataSourceID="Buildings" DataTextField="Building_Name"
DataValueField="Building_ID"></asp:DropDownList>
</td>
</tr>
<tr>
<td style="text-align: left;"><label for="ta_Description" style="white-space: nowrap;">Description</label></td>
<td style="text-align: right;" colspan="3"><textarea id="ta_Description" runat="server" cols="50" rows="3"></textarea></td>
</tr>
<tr>
<td colspan="4" style="text-align: right;">
<asp:Button ID="btn_Add" Text="Add" CssClass="ui-state-default ui-corner-all" runat="server" OnClick="btn_Add_Click" />
</td>
</tr>
</tbody>
</table>
</fieldset>
</div>
</ContentTemplate>
</asp:UpdatePanel>
<p></p>
<fieldset style="display: inline-block; padding: 5px; -moz-border-radius: 8px; border-radius: 8px;">
<legend style="text-decoration: underline;">[ Update Equipment ]</legend>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:SIMON-Writer %>"
DeleteCommand="DELETE FROM [Network_Equipment] WHERE [Network_Equipment_ID] = @original_Network_Equipment_ID"
OldValuesParameterFormatString="original_{0}"
SelectCommand="SELECT * FROM [All_Network_Equipment-Simplified]"
UpdateCommand="UPDATE [Network_Equipment] SET [Network_Equipment_Name] = @Network_Equipment_Name, [Network_Equipment_Type_ID] = @Network_Equipment_Type_ID, [IP_Address] = @IP_Address, [FQDN] = @FQDN, [NetBIOS_Name] = @NetBIOS_Name, [Building_ID] = @Building_ID, [Description] = @Description, [Active] = @Active WHERE [Network_Equipment_ID] = @original_Network_Equipment_ID">
<DeleteParameters>
<asp:Parameter Name="original_Network_Equipment_ID" Type="Int32" />
</DeleteParameters>
<InsertParameters>
<asp:Parameter Name="Network_Equipment_Name" Type="String" />
<asp:Parameter Name="Network_Equipment_Type_ID" Type="Int32" />
<asp:Parameter Name="IP_Address" Type="String" />
<asp:Parameter Name="FQDN" Type="String" />
<asp:Parameter Name="NetBIOS_Name" Type="String" />
<asp:Parameter Name="Building_ID" Type="Int32" />
<asp:Parameter Name="Description" Type="String" />
<asp:Parameter Name="Active" Type="Boolean" />
</InsertParameters>
<UpdateParameters>
<asp:Parameter Name="Network_Equipment_Name" Type="String" />
<asp:Parameter Name="Network_Equipment_Type_ID" Type="Int32" />
<asp:Parameter Name="IP_Address" Type="String" />
<asp:Parameter Name="FQDN" Type="String" />
<asp:Parameter Name="NetBIOS_Name" Type="String" />
<asp:Parameter Name="Building_ID" Type="Int32" />
<asp:Parameter Name="Description" Type="String" />
<asp:Parameter Name="Active" Type="Boolean" />
<asp:Parameter Name="original_Network_Equipment_ID" Type="Int32" />
</UpdateParameters>
</asp:SqlDataSource>
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
CellPadding="4" DataKeyNames="Network_Equipment_ID"
DataSourceID="SqlDataSource1" ForeColor="#333333" GridLines="None">
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
<Columns>
<asp:BoundField DataField="Network_Equipment_ID"
HeaderText="Network_Equipment_ID" ReadOnly="True"
SortExpression="Network_Equipment_ID" Visible="False" />
<asp:BoundField DataField="Network_Equipment_Name" HeaderText="Equipment Name" SortExpression="Network_Equipment_Name" />
<asp:BoundField DataField="Network_Equipment_Type_ID" HeaderText="Network_Equipment_Type_ID" SortExpression="Network_Equipment_Type_ID" Visible="False" />
<asp:TemplateField HeaderText="Equipment Type" SortExpression="Network_Equipment_Type">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList1" runat="server"
DataSourceID="Network_Equipment_Type" DataTextField="Network_Equipment_Type"
DataValueField="Network_Equipment_Type_ID"
SelectedValue='<%# Bind("Network_Equipment_Type_ID") %>'>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("Network_Equipment_Type") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="IP_Address" HeaderText="IP Address" SortExpression="IP_Address" />
<asp:BoundField DataField="FQDN" HeaderText="FQDN" SortExpression="FQDN" />
<asp:BoundField DataField="NetBIOS_Name" HeaderText="NetBIOS Name" SortExpression="NetBIOS_Name" />
<asp:BoundField DataField="Building_ID" HeaderText="Building_ID" SortExpression="Building_ID" Visible="False" />
<asp:TemplateField HeaderText="Building" SortExpression="Building_Name">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList2" runat="server" DataSourceID="Buildings"
DataTextField="Building_Name" DataValueField="Building_ID"
SelectedValue='<%# Bind("Building_ID") %>'>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("Building_Name") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Description" SortExpression="Description">
<EditItemTemplate>
<asp:TextBox ID="TextBox3" runat="server" Height="50px" Text='<%# Bind("Description") %>' TextMode="MultiLine" Width="200px"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label3" runat="server" Text='<%# Bind("Description") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:CheckBoxField DataField="Active" HeaderText="Active" SortExpression="Active" />
<asp:CommandField ShowEditButton="True" />
</Columns>
<EditRowStyle BackColor="#999999" />
<FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
<RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
<SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
<SortedAscendingCellStyle BackColor="#E9E7E2" />
<SortedAscendingHeaderStyle BackColor="#506C8C" />
<SortedDescendingCellStyle BackColor="#FFFDF8" />
<SortedDescendingHeaderStyle BackColor="#6F8DAE" />
</asp:GridView>
<br />
<asp:SqlDataSource ID="Network_Equipment_Type" runat="server" ConnectionString="<%$ ConnectionStrings:SIMON-Reader %>"
SelectCommand="SELECT DISTINCT * FROM [Network_Equipment_Types] ORDER BY [Network_Equipment_Type]">
</asp:SqlDataSource>
<asp:SqlDataSource ID="Buildings" runat="server" ConnectionString="<%$ ConnectionStrings:SIMON-Reader %>"
SelectCommand="SELECT DISTINCT * FROM [Buildings] ORDER BY [Building_Name]">
</asp:SqlDataSource>
</ContentTemplate>
</asp:UpdatePanel>
</fieldset>
</div>
</form>
</body>
</html>
设备.aspx.cs
namespace SIMON
{
public partial class Equipment : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btn_Add);
btn_Add.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button ui-corner-all'); ";
btn_Add.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
}
}
protected void btn_Add_Click(object sender, EventArgs e)
{
error.InnerHtml = " ";
SqlTransaction trans = null;
using (SqlConnection MyConn = new SqlConnection(ConfigurationManager.ConnectionStrings["SIMON-Writer"].ToString()))
{
MyConn.Open();
trans = MyConn.BeginTransaction();
string sqlStatement = "INSERT INTO [Network_Equipment] "
+ "([Network_Equipment_Name], [Network_Equipment_Type_ID], [IP_Address], [FQDN], [NetBIOS_Name], [Building_ID], [Description])"
+ " VALUES "
+ "(@Network_Equipment_Name, @Network_Equipment_Type_ID, @IP_Address, @FQDN, @NetBIOS_Name, @Building_ID, @Description)";
using (SqlCommand sqlCmd = new SqlCommand(sqlStatement, MyConn))
{
sqlCmd.Transaction = trans;
sqlCmd.Connection = MyConn;
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Name", ((in_Add_Equipment.Value == null) ? (object)DBNull.Value : (object)in_Add_Equipment.Value));
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Type_ID", ((ddl_Equipment_Type.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Equipment_Type.SelectedValue));
sqlCmd.Parameters.AddWithValue("@IP_Address", ((in_IP_Address.Value == null) ? (object)DBNull.Value : (object)in_IP_Address.Value));
sqlCmd.Parameters.AddWithValue("@FQDN", ((in_FQDN.Value == null) ? (object)DBNull.Value : (object)in_FQDN.Value));
sqlCmd.Parameters.AddWithValue("@NetBIOS_Name", ((in_NetBIOS.Value == null) ? (object)DBNull.Value : (object)in_NetBIOS.Value));
sqlCmd.Parameters.AddWithValue("@Building_ID", ((ddl_Building.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Building.SelectedValue));
sqlCmd.Parameters.AddWithValue("@Description", ((ta_Description.Value == null) ? (object)DBNull.Value : (object)ta_Description.Value));
try
{
sqlCmd.ExecuteNonQuery();
trans.Commit();
}
catch (Exception er)
{
error.InnerHtml = er.ToString();
return;
}
finally
{
MyConn.Close();
error.InnerHtml = "Successfully added: " + in_Add_Equipment.Value;
in_Add_Equipment.Value = "";
ddl_Equipment_Type.SelectedIndex = 0;
in_IP_Address.Value = "";
in_FQDN.Value = "";
in_NetBIOS.Value = "";
ddl_Building.SelectedIndex = 0;
ta_Description.Value = "";
GridView1.DataBind();
}
}
}
}
}
}
-------- 编辑 2 --------
我已经找到了导致这段代码的 SQL 语句“双重执行”的原因:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btn_Add);
btn_Add.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button ui-corner-all'); ";
btn_Add.OnClientClick = ClientScript.GetPostBackEventReference(optionsSubmit);
}
}
当我注释掉它时，信息被添加一次，但按钮并没有像我想要的那样被禁用。禁用该按钮将防止人们不耐烦并多次单击该按钮。
建议？
这是我得到的:
aspx
<asp:Button ID="btn_Add" Text="Add" CssClass="ui-state-default ui-corner-all" runat="server" OnClick="btn_Add_Click" />
aspx.cs
if (!Page.IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btn_Add);
btn_Add.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button ui-corner-all'); ";
btn_Add.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
}
执行两次SQL语句
aspx
<asp:Button ID="btn_Add" Text="Add" CssClass="ui-state-default ui-corner-all" runat="server" />
aspx.cs
if (!Page.IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btn_Add);
btn_Add.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button ui-corner-all'); ";
btn_Add.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
}
以所需的方式简要更改“btn_Add”，但不执行“btn_Add_Click”的代码
aspx
<asp:Button ID="btn_Add" Text="Add" CssClass="ui-state-default ui-corner-all" runat="server" OnClick="btn_Add_Click" />
aspx.cs
if (!Page.IsPostBack)
{
PostBackOptions optionsSubmit = new PostBackOptions(btn_Add);
btn_Add.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button ui-corner-all'); ";
//btn_Add.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
}
以所需的方式更改“btn_Add”，不执行“btn_Add_Click”的代码，并将整个页面刷新为 Equipment.aspx(通常 Equipment.aspx 通过 jquery .load 事件加载到 div 中)
最佳答案
一些建议...
连接字符串应存储在您的 web.config 文件中。
可以捕获过程中每一步的异常，但要使用“using”语句。这样您就不必担心处置您的对象。
我建议将 Global.asax 文件添加到您的项目并在那里捕获应用程序错误。在您的 catch 语句中，您可以放置一行并说“throw new Exception..”并传入您的特定异常，以便轻松捕获并描述错误。然后我建议在 Enterprise Library 5.0 中设置日志记录应用程序 block 。拥有像您这样的全局“错误”变量可能不是一个好主意。如果您想轻松学习 Enterprise Library，请下载 Enterprise Library Labs 示例。
我不会在您的代码中直接使用 SQL 命令。我会使用存储过程，并让 SQL 在 SQL 服务器本身上完成。如果您有变量，请在存储过程中设置参数。存储过程对于您的 Web 应用程序来说更安全。使用 Microsoft 企业库中的数据库应用程序 block 甚至可能是个好主意。他们为您提供了所有这些代码，您只需要导入库并了解命令即可。他们为您处理所有性能影响。
如果使用 using 语句，则无需关闭连接或释放。我在代码中删除了它。
如果您抛出异常，则不需要“return”语句...下一个符合条件的 catch 语句(或 finally 语句)将捕获它。如果没有，则 Global.asax 中的 Application_Error 将捕获它。确保在 .NET 框架中正确处理未处理的异常。 Microsoft 打破了 .NET 3.5 未处理的异常架构，因此您要么必须添加自己的模块，要么切换回 1.1 架构。或者升级到 .NET 4.0。
实际问题:您的点击事件可能会被调用两次，因为您正在使用处理程序并且您在
这是#1:
这是#2: btn_Add.OnClientClick = ClientScript.GetPostBackEventReference(optionsSubmit);
如果您的控件具有 onclick 属性，则无需添加特殊代码(如 OnClientClick 或事件处理程序)。只需使用其中之一即可。
祝你好运!
error.InnerHtml = " ";
string connStr = "Data Source=.\\SQLEXPRESS;"
+ "Initial Catalog=SIMON;"
+ "Persist Security Info=True;"
+ "User ID=username;Password=password");
using (SqlConnection MyConn = new SqlConnection(connStr))
{
string sqlStatement = @"INSERT INTO [Network_Equipment] "
+ "([Network_Equipment_Name], [Network_Equipment_Type_ID], [IP_Address], [FQDN], [NetBIOS_Name], [Building_ID], [Description])"
+ " VALUES "
+ "(@Network_Equipment_Name, @Network_Equipment_Type_ID, @IP_Address, @FQDN, @NetBIOS_Name, @Building_ID, @Description)";
SqlCommand sqlCmd = new SqlCommand(sqlStatement, MyConn);
sqlCmd.Connection = MyConn;
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Name", ((in_Add_Equipment.Value == null) ? (object)DBNull.Value : (object)in_Add_Equipment.Value));
sqlCmd.Parameters.AddWithValue("@Network_Equipment_Type_ID", ((ddl_Equipment_Type.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Equipment_Type.SelectedValue));
sqlCmd.Parameters.AddWithValue("@IP_Address", ((in_IP_Address.Value == null) ? (object)DBNull.Value : (object)in_IP_Address.Value));
sqlCmd.Parameters.AddWithValue("@FQDN", ((in_FQDN.Value == null) ? (object)DBNull.Value : (object)in_FQDN.Value));
sqlCmd.Parameters.AddWithValue("@NetBIOS_Name", ((in_NetBIOS.Value == null) ? (object)DBNull.Value : (object)in_NetBIOS.Value));
sqlCmd.Parameters.AddWithValue("@Building_ID", ((ddl_Building.SelectedValue == null) ? (object)DBNull.Value : (object)ddl_Building.SelectedValue));
sqlCmd.Parameters.AddWithValue("@Description", ((ta_Description.Value == null) ? (object)DBNull.Value : (object)ta_Description.Value));
try
{
MyConn.Open();
}
catch (Exception er)
{
//error.InnerHtml = er.ToString();
//return;
throw new Exception(...
}
try
{
sqlCmd.ExecuteNonQuery();
}
catch (Exception er)
{
//error.InnerHtml = er.ToString();
//return;
throw new Exception(...
}
error.InnerHtml = "Successfully added: " + in_Add_Equipment.Value;
}
in_Add_Equipment.Value = "";
ddl_Equipment_Type.SelectedIndex = 0;
in_IP_Address.Value = "";
in_FQDN.Value = "";
in_NetBIOS.Value = "";
ddl_Building.SelectedIndex = 0;
ta_Description.Value = "";
GridView1.DataBind();
关于c# - SqlCommand SQL 语句被执行两次，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/6687844/