Using function recursion to implement dynamic tree menu based on PHP and MySQL_PHP tutorial

    树型菜单在很多桌面应用系统中都有非常广泛的应用，其主要优点是结构清晰，利于使用者非常清楚的知道目前自己所在的位置。但在web上树型菜单的应用因为没有理想的现成组件可以拿过来直接使用，所以一般的情况下，程序员主要是通过JavaScript来实现一些简单的树型结构菜单，但这些菜单往往都是事先定好各菜单项目，以及各菜单项目之间的层次关系，不利于扩充，一旦需要另一个菜单结构时，往往还需要重新编写，因此使用起来不是很方便。

    经过对函数递归的研究，我发现这种树型菜单可以通过递归函数，使树型菜单的显示实现动态变化，并没有级数的限制。下面就是我用php,MySQL,JavaScript写的一个动态树型菜单的处理代码，如果大家有兴趣的话，就和我一起来看看我是如何实现的吧：）

首先，我们需要一个数据库，在这个数据库中，我们建立以下一张表：

CREATE TABLE menu (
id tinyint(4) NOT NULL auto_increment,
parent_id tinyint(4) DEFAULT '0' NOT NULL,
name varchar(20),
url varchar(60),
PRIMARY KEY (id)
);

这张表中
id 为索引
parent_id 用来保存上一级菜单的id号，如果是一级菜单则为0
name 为菜单的名称，也就是要在页面上显示的菜单内容
url 如果某菜单为末级菜单，则需要指定该连接的url地址，这个字段就是用来保存此地址的，其他非末级菜单，该字段为空

好了，数据库有了，你就可以添加一些记录了，下面是我做测试的时候，使用的一些记录：

INSERT INTO menu VALUES ( '1', '0', '人事管理', '');
INSERT INTO menu VALUES ( '2', '0', '通讯交流', '');
INSERT INTO menu VALUES ( '3', '1', '档案管理', '');
INSERT INTO menu VALUES ( '4', '1', '考勤管理', 'http://localhost/personal/attendance.php');
INSERT INTO menu VALUES ( '5', '2', '通讯录', '');
INSERT INTO menu VALUES ( '6', '2', '网络会议', '');
INSERT INTO menu VALUES ( '7', '3', '新增档案', 'http://localhost/personal/add_achive.php');
INSERT INTO menu VALUES ( '8', '3', '查询档案', 'http://localhost/personal/search_archive.php');
INSERT INTO menu VALUES ( '9', '3', '删除档案', 'http://localhost/personal/delete_archive.php');
INSERT INTO menu VALUES ( '10', '5', '新增通讯记录','http://localhost/communication/add_address.php');
INSERT INTO menu VALUES ( '11', '5', '查询通讯记录', http://localhost/communication/search_address.php');
INSERT INTO menu VALUES ( '12', '5', '删除通讯记录', http://localhost/communication/delete_address.php');
INSERT INTO menu VALUES ( '13', '6', '召开会议', 'http://localhost/communication/convence_meeting.php');
INSERT INTO menu VALUES ( '14', '6', '会议查询', 'http://localhost/communication/search_meeting.php');

在添加记录的时候，一定要注意，非一级菜单的parent_id一定要指定为上级菜单的ID号，否则你的菜单是不会显示出来的：）

好了！有了数据库，下面就是通过php,JavaScript把菜单从数据库中读出来，并显示出来了：）

1、JavaScript脚本：
function ShowMenu(MenuID)
{
if(MenuID.style.display=="none")
{
MenuID.style.display="";
}
else
{
MenuID.style.display="none";
}
}

这个脚本很简单，就是用来响应点击某个菜单被点击的事件的。

2、CSS文件：

TD {
FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; LINE-HEIGHT: 130%; letter-spacing:1px
}

A:link {
COLOR: #990000; FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; TEXT-DECORATION: none; letter-spacing:1px
}
A:visited {
COLOR: #990000; FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; TEXT-DECORATION: none; letter-spacing:1px
}
A:active {
COLOR: #990000; FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; TEXT-DECORATION: none; letter-spacing:1px
}
A:hover {
COLOR: #ff0000; FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; TEXT-DECORATION: underline; letter-spacing:1px
}

.Menu {
COLOR:#000000; FONT-FAMILY: "Verdana", "宋体"; FONT-SIZE: 12px; CURSOR: hand
}

定义了一些基本的样式信息，比如字体，颜色，超级连接的样式等，如果你想改变样式的话，只要修改这里就行了！

3、下面就是我的php页面了！

//Basic variable settings
$GLOBALS["ID"] =1; / /Used to track the ID number of the drop-down menu
$layer=1; //Used to track the level of the current menu

//Connect to the database
$Con=mysql_connect("localhost"," root","");
mysql_select_db("work");

//Extract the first-level menu
$sql="select * from menu where parent_id=0";
$ result=mysql_query($sql,$Con);

//If the first-level menu exists, start the display of the menu
if(mysql_num_rows($result)>0) ShowTreeMenu($Con,$result ,$layer,$ID);

//================================ ==============
//Show tree menu function ShowTreeMenu($con,$result,$layer)
//$con: database connection
// $result: The menu record set that needs to be displayed
//layer: The level of the menu that needs to be displayed
//======================== =======================
function ShowTreeMenu($Con,$result,$layer)
{
//Get the required display The number of menu items
$numrows=mysql_num_rows($result);

//Start to display the menu, each submenu is represented by a table
echo "

";

for($rows=0;$rows<$numrows;$rows++)
{
//Change the current menu item The content of the import array
$menu=mysql_fetch_array($result);

//Extract the submenu record set of the menu item
$sql="select * from menu where parent_id=$menu[id ]";
$result_sub=mysql_query($sql,$Con);

echo "

";
//If the menu item has a submenu, add a JavaScript onClick statement
if(mysql_num_rows($result_sub)>0)
{
echo "";
echo "";
echo "

";

//If this If the menu item has a submenu, the submenu will be displayed
if(mysql_num_rows($result_sub)>0)
{
//Specify the ID and style of the submenu to correspond to the onClick statement
echo "

";
echo "";
}
//Continue to display the next menu item
}
echo "

	"; } else { echo "		"; } //If the menu item has no submenu and a hyperlink address is specified, it is specified as a hyperlink. //Otherwise Show only menu name if($menu[url]!="") echo "$menu[name]"; else echo $menu[name]; echo "
< /td>"; echo "	"; //Increase the series by 1 $layer++; //Recursively call the ShowTreeMenu() function to generate a submenu ShowTreeMenu($Con,$result_sub,$layer); //The submenu processing is completed, return to the previous level of recursion, and reduce the series by 1 $layer--; echo "< /td>

";
}
?> ;

In the above php page, I defined a function ShowTreeMenu(). Through the call of this function, it will be displayed from Each menu item is called up recursively in the database and displayed on the page:)