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<!doctype html>
<html lang="en" class="page-type-section">
<head prefix="og: http://ogp.me/ns#">
<meta charset="utf-8">
<title>if, else, elseif - FreeMarker 手册</title>
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<meta property="og:title" content="if, else, elseif">
<meta property="og:locale" content="en_US">
<meta property="og:url" content="http://freemarker.org/docs/ref_directive_if.html">
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<div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="ref_directive_global.html"><span>Previous</span></a><a class="paging-arrow next" href="ref_directive_import.html"><span>Next</span></a></div><div class="title-wrapper">
<h1 class="content-header header-section1" id="ref_directive_if" itemprop="headline">if, else, elseif</h1>
</div></div><div class="page-menu">
<div class="page-menu-title">Page Contents</div>
<ul><li><a class="page-menu-link" href="#autoid_85" data-menu-target="autoid_85">概要</a></li><li><a class="page-menu-link" href="#autoid_86" data-menu-target="autoid_86">描述</a></li></ul> </div><a name="ref.directive.if"></a><a name="ref.directive.else"></a><a name="ref.directive.elseif"></a>
<h2 class="content-header header-section2" id="autoid_85">概要</h2>
<pre class="metaTemplate">
<code class="inline-code"><#if <em class="code-color">condition</em>>
<em class="code-color">...</em>
<#elseif <em class="code-color">condition2</em>>
<em class="code-color">...</em>
<#elseif <em class="code-color">condition3</em>>
<em class="code-color">...</em>
<em class="code-color">...</em>
<#else>
<em class="code-color">...</em>
</#if></code>
</pre>
<p>这里：</p>
<ul>
<li>
<code class="inline-code"><em class="code-color">condition</em></code>,
<code class="inline-code"><em class="code-color">condition2</em></code>，
等：将被计算成布尔值的表达式。
</li>
</ul>
<p><code class="inline-code">elseif</code> 和
<code class="inline-code">else</code> 是可选的。</p>
<h2 class="content-header header-section2" id="autoid_86">描述</h2>
<p>你可以使用 <code class="inline-code">if</code>， <code class="inline-code">elseif</code>
和 <code class="inline-code">else</code> 指令来条件判断是否越过模板的一个部分。
<code class="inline-code"><em class="code-color">condition</em></code> 必须计算成布尔值，
否则错误将会中止模板处理。<code class="inline-code">elseif</code> 和
<code class="inline-code">else</code> 必须出现在 <code class="inline-code">if</code> 内部
(也就是，在 <code class="inline-code">if</code> 的开始标签和结束标签之间)。
<code class="inline-code">if</code> 中可以包含任意数量的
<code class="inline-code">elseif</code>(包括0个) 而且结束时
<code class="inline-code">else</code> 是可选的。比如：</p>
<p>只有 <code class="inline-code">if</code> 没有 <code class="inline-code">elseif</code> 和
<code class="inline-code">else</code>：</p>
<div class="code-wrapper"><pre class="code-block code-template"><#if x == 1>
x is 1
</#if></pre></div>
<p>只有 <code class="inline-code">if</code> 没有 <code class="inline-code">elseif</code> 但是有
<code class="inline-code">else</code>：</p>
<div class="code-wrapper"><pre class="code-block code-template"><#if x == 1>
x is 1
<#else>
x is not 1
</#if></pre></div>
<p>有 <code class="inline-code">if</code> 和两个 <code class="inline-code">elseif</code> 但是没有
<code class="inline-code">else</code>：</p>
<div class="code-wrapper"><pre class="code-block code-template"><#if x == 1>
x is 1
<#elseif x == 2>
x is 2
<#elseif x == 3>
x is 3
</#if></pre></div>
<p>有 <code class="inline-code">if</code> 和三个 <code class="inline-code">elseif</code> 还有
<code class="inline-code">else</code>:</p>
<div class="code-wrapper"><pre class="code-block code-template"><#if x == 1>
x is 1
<#elseif x == 2>
x is 2
<#elseif x == 3>
x is 3
<#elseif x == 4>
x is 4
<#else>
x is not 1 nor 2 nor 3 nor 4
</#if></pre></div>
<p>要了解更多布尔表达式，可以参考：<a href="dgui_template_exp.html">模板开发指南/模板/表达式</a>.</p>
<p>你(当然)也可以嵌套 <code class="inline-code">if</code> 指令：</p>
<div class="code-wrapper"><pre class="code-block code-template"><#if x == 1>
x is 1
<#if y == 1>
and y is 1 too
<#else>
but y is not
</#if>
<#else>
x is not 1
<#if y < 0>
and y is less than 0
</#if>
</#if></pre></div>
<div class="callout note">
<strong class="callout-label">Note:</strong>
<p>当你想测试是否 <code class="inline-code">x > 0</code> 或
<code class="inline-code">x >= 0</code>，编写 <code class="inline-code"><#if x >
0></code> 和 <code class="inline-code"><#if x >= 0></code> 是错误的，
因为第一个 <code class="inline-code">></code> 会结束
<code class="inline-code">#if</code> 标签。要这么来做，可以编写
<code class="inline-code"><#if x gt 0></code> 或 <code class="inline-code"><#if gte
0></code>。也请注意，如果比较发生在括号内部，那么就没有这样的问题，
比如 <code class="inline-code"><#if
foo.bar(x > 0)></code> 就会得到想要的结果。</p>
</div>
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