在使用的过程中，我们经常需要显示文章的缩略图。WordPress 缩略图的实现主要靠两种方式，第一种是来作为缩略图的图源，第二种是读取文章特色图标来作为缩略图的图源。今天我们将这两种方式结合起来实现 wordpress 缩略图。
实现原理如下：
一、判断文章是否已经设置特色图片，如果设置了，则获取特色图片来作为文章缩略图的图源。
二、判断文章中是否存在图片（正则表达式），如果存在图片，则获取文章中第一张图片来来作为文章缩略图的图源。
三、如果文章中既没有设置特色图片，也不存在图片，则显示一张默认的图片。
实现方法如下：
1. 切换到主题目录，打开functions.PHP文件，加入以下代码：
Crayon-5c891d2adc09e867661676" class="Crayon-Syntax Crayon-theme-classic Crayon-font-monaco Crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouSEOver" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
Crayon-toolbar" data-settings=" mouSEOver overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">Crayon-title">
Crayon-tools" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">Crayon-mixed-highlight" title="Contains Mixed Languages">
Crayon-button Crayon-nums-button" title="Toggle Line Numbers">
Crayon-button-icon">
Crayon-button Crayon-plain-button" title="Toggle Plain Code">
Crayon-button-icon">
Crayon-button Crayon-wrap-button" title="Toggle Line Wrap">
Crayon-button-icon">
Crayon-button Crayon-expand-button" title="Expand Code">
Crayon-button-icon">
Crayon-button Crayon-copy-button" title="Copy">
Crayon-button-icon">
Crayon-button Crayon-popup-button" title="Open Code In New Window">
Crayon-language">PHPCrayon-button-icon">
Crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
Crayon-plain-wrap">
Crayon-main" style="">Crayon-table">
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Crayon-line Crayon-striped-line" id="Crayon-5c891d2adc09e867661676-10">Crayon-h">Crayon-sy">}Crayon-h"> Crayon-st">elseCrayon-h"> Crayon-sy">{Crayon-h"> Crayon-line" id="Crayon-5c891d2adc09e867661676-11">Crayon-h">Crayon-v">$contentCrayon-h"> Crayon-o">=Crayon-h"> Crayon-v">$postCrayon-i">post_contentCrayon-sy">; Crayon-line Crayon-striped-line" id="Crayon-5c891d2adc09e867661676-12">Crayon-h">Crayon-v">$defaltthubmnailCrayon-h"> Crayon-o">=Crayon-h"> Crayon-e">sapphireCrayon-sy">(Crayon-s">'default-thumb'Crayon-sy">)Crayon-h"> Crayon-sy">?Crayon-h"> Crayon-e">sapphireCrayon-sy">(Crayon-s">'default-thumb'Crayon-sy">)Crayon-h"> Crayon-o">:Crayon-h"> Crayon-e">get_template_directory_uriCrayon-sy">(Crayon-sy">)Crayon-sy">.Crayon-s">'/img/no-thumb.png'Crayon-sy">; Crayon-line" id="Crayon-5c891d2adc09e867661676-13">Crayon-h">Crayon-e">preg_match_allCrayon-sy">('Crayon-o">/Crayon-o"><Crayon-i">imgCrayon-sy">.Crayon-o">*Crayon-sy">?Crayon-sy">(Crayon-sy">?Crayon-o">:Crayon-h"> Crayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">tCrayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">rCrayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">nCrayon-sy">)Crayon-sy">?Crayon-i">srcCrayon-o">=Crayon-sy">[Crayon-sy">\'Crayon-s">"]?(.+?)[\'"Crayon-sy">]Crayon-sy">?Crayon-sy">(Crayon-sy">?Crayon-o">:Crayon-sy">(Crayon-sy">?Crayon-o">:Crayon-h"> Crayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">tCrayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">rCrayon-o">|Crayon-sy">\Crayon-sy">\Crayon-i">nCrayon-sy">)Crayon-o">+Crayon-sy">.Crayon-o">*Crayon-sy">?Crayon-sy">)Crayon-o">/Crayon-i">simCrayon-s">',PREG_PATTERN_ORDER); Crayon-line Crayon-striped-line" id="Crayon-5c891d2adc09e867661676-14">Crayon-s">$n = count($strResult[1]); Crayon-line" id="Crayon-5c891d2adc09e867661676-15"> 0){ Crayon-line Crayon-striped-line" id="Crayon-5c891d2adc09e867661676-16">Crayon-s">echo 'Crayon-o"><Crayon-e">img Crayon-i">srcCrayon-o">=Crayon-s">"'.get_bloginfo("Crayon-i">template_urlCrayon-s">").'/timthumb.PHP?w='.$width.'&h='.$height.'&src='.$strResult[1][0].'"Crayon-h"> Crayon-i">titleCrayon-o">=Crayon-s">"'.get_the_title().'"Crayon-h"> Crayon-i">altCrayon-o">=Crayon-s">"'.get_the_title().'"Crayon-o">/Crayon-s">'; Crayon-line" id="Crayon-5c891d2adc09e867661676-17">Crayon-s">} else { Crayon-line Crayon-striped-line" id="Crayon-5c891d2adc09e867661676-18">Crayon-s">echo 'Crayon-o"><Crayon-e">img Crayon-i">srcCrayon-o">=Crayon-s">"'.get_bloginfo("Crayon-i">template_urlCrayon-s">").'/timthumb.PHP?w='.$width.'&h='.$height.'&src='.$defaltthubmnail.'"Crayon-h"> Crayon-i">titleCrayon-o">=Crayon-s">"'.get_the_title().'"Crayon-h"> Crayon-i">altCrayon-o">=Crayon-s">"'.get_the_title().'"Crayon-o">/'Crayon-sy">; Crayon-line" id="Crayon-5c891d2adc09e867661676-21">Crayon-sy">} 注：此处需要用到一个裁剪缩略图的PHP文件，点击下面的链接下载 Crayon-5c891d2adc0a9150737020" class="Crayon-Syntax Crayon-theme-classic Crayon-font-monaco Crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouSEOver" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;"> Crayon-toolbar" data-settings=" mouSEOver overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">Crayon-title"> Crayon-tools" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">Crayon-mixed-highlight" title="Contains Mixed Languages"> Crayon-button Crayon-nums-button" title="Toggle Line Numbers"> Crayon-button-icon"> Crayon-button Crayon-plain-button" title="Toggle Plain Code"> Crayon-button-icon"> Crayon-button Crayon-wrap-button" title="Toggle Line Wrap"> Crayon-button-icon"> Crayon-button Crayon-expand-button" title="Expand Code"> Crayon-button-icon"> Crayon-button Crayon-copy-button" title="Copy"> Crayon-button-icon"> Crayon-button Crayon-popup-button" title="Open Code In New Window"> Crayon-button-icon"> Crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;"> Crayon-plain-wrap"> Crayon-main" style="">
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