php分页

无论写了多少遍，无论编程的技术到了何种的境界，还是会涉及到一种需求：分页。

很多的分页代码都会有很多的判断，是不是第一页，是不是最后一页等，今天在惠新宸的博客上看见一种巧妙的算法，通过简单的比较代替了很多的判断，试了很久，很难写出比这个更简单的代码了。下面是自己研究后自己重新敲了一遍的代码：

class Pagination
{
    private $page,$page_size,$total,$total_page,$size;
    private $prev_str = '<',$next_str = '>';
    private $class = 'page',$prev_class = 'prev',$next_class = 'next',$selected_class = 'selected',
            $no_prev_class = 'no-prev',$no_next_class = 'no-next';
    private $para_name = 'page',$url_prefix = '',$target  = '';
    private $page_str = array();

    function __construct($url_prefix,$page_size,$total,$size=10,$conf=array())
    {
        $this->url_prefix = $url_prefix;
        $this->page_size = $page_size;
        $this->total = $total;
        $this->total_page = intval(ceil($total/$page_size));
        $this->size = $size;
        if( ! empty($conf)){
            $configure = array('prev_str','next_str','class','selected_class');
            foreach($conf as $key => $val){
                if(in_array($val,$configure)){
                    $this->$key = $val;
                }
            }
        }
        if(strstr($url_prefix,'?') === false){
            $this->url_prefix .= '?' . $this->para_name . '=';
        }else{
            $this->url_prefix .= '&' . $this->para_name . '=';
        }
    }

    function generate($page){
        $this->page = $page;
        if(isset($this->page_str[$page])){
            return $this->page_str[$page];
        }
        $half = intval($this->size/2);
        $page_start = max(1,$this->page - $half);
        $page_end = min($page_start + $this->size - 1,$this->total_page);
        $page_start = max(1, $page_end - $this->size + 1);

        $this->page_str[$page] = $this->build_nav_str($page_start,$page_end);
        return $this->page_str[$page];
    }

    function build_nav_str($page_start,$page_end){
        $page_nums = range($page_start,$page_end);
        if($this->page == 1){
            $page_str = <<{$this->prev_str}
HTML;
        }else{
            $page = $this->page - 1;
            $page_str = <<target}>{$this->prev_str}
HTML;
        }
        foreach($page_nums as $p){
            $page_str .= ($p == $this->page) ? <<
                    {$p}
                
HTML
            :<<
                    target}>{$p}
                
HTML;
        }
        if($this->page == $this->total_page){
            $page_str .= <<{$this->next_str}
HTML;
        }else{
            $page = $this->page + 1;
            $page_str .= <<
                    target}>{$this->next_str}
                
HTML;
        }
        return $page_str;
    }
}

里面有几个关键的地方：

1. generate方法里的起始页和结束页计算方法。
2. page和generate方法分开，批量生成分页代码的时候节省内存。
3. nowdoc的使用，使得html代码可以着色，容易识别。