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            <a href="/2022/06/07/z-index/" class="post-title-link" itemprop="url">z-index 跨级不生效</a>
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              <span class="post-meta-item-text">发表于</span>

              <time title="创建时间：2022-06-07 00:00:00" itemprop="dateCreated datePublished" datetime="2022-06-07T00:00:00+08:00">2022-06-07</time>
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          <p>在CSS世界中，z-index属性和定位元素在一起可以控制z轴顺序。理论上，数值越大层级越高。但在实际使用中会有很多细节需要注意。</p>
<h2 id="背景描述"><a href="#背景描述" class="headerlink" title="背景描述"></a>背景描述</h2><p>在一个小程序项目中有这样的一个需求：页面包含一个元素A和一个列表B，需要实现列表B的一部分在元素A之上，一部分在元素A之下。<br>基于组件封装的思想，一般的做法是：元素A是一个组件，列表B是另外一个组件。但是在这种布局下，发现无论如何调整元素A、列表B以及子元素的<code>z-index</code>，都无法满足“列表B的一部分在元素A之上，一部分在元素A之下”的效果。</p>
<img src="/images/z-index-1.jpg" alt="表现异常" style="width:400px;"/>

<p>图中的上半部分是预期表现，而下半部分是实际表现。可以看到，列表B要不整个在元素A之上，要不就是整个在元素A之下。</p>
<p><a target="_blank" rel="noopener" href="https://developers.weixin.qq.com/s/LTk5QQmr72zM">小程序代码片段</a></p>
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            <a href="/2022/05/26/miniprogram-canvas-metrics/" class="post-title-link" itemprop="url">小程序真机下 canvas metrics 无法获取字体高度的问题</a>
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          <p>小程序真机下会出现<code>canvas</code> <code>metrics</code> 无法获取字体高度的问题，模拟器下表现正常。</p>
<h2 id="背景描述"><a href="#背景描述" class="headerlink" title="背景描述"></a>背景描述</h2><p>在一个项目下需要在<code>canvas</code>中对一行文本垂直居中展示，以下是一个示例效果：</p>
<img src="/images/miniprogram-canvas-metrics-1.jpg" alt="文本垂直居中展示" style="width:400px;"/>

<p>在模拟器上的表现很正常，但是到了真机上后文本位置出现严重的偏差。验证了iOS设备和Android设备都无法按预期做到垂直居中展示。</p>
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            <a href="/2022/05/17/miniprogram-canvas-z-index/" class="post-title-link" itemprop="url">小程序模拟器下 canvas z-index 显示异常的问题</a>
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              <time title="创建时间：2022-05-17 00:00:00" itemprop="dateCreated datePublished" datetime="2022-05-17T00:00:00+08:00">2022-05-17</time>
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          <p>小程序模拟器下会出现 canvas z-index 显示异常，真机下表现正常。</p>
<h2 id="背景描述"><a href="#背景描述" class="headerlink" title="背景描述"></a>背景描述</h2><p>在一个项目下需要做一个环形的动画，中间围绕的部分是一个<code>canvas</code>对象，在模拟器上无论如何设置<code>z-index</code>，<code>canvas</code>对象始终都显示在最上层。</p>
<img src="/images/miniprogram-canvas-z-index-1.jpg" alt="表现异常" style="width:400px;"/>

<p>在模拟器上的渲染效果如上图，而实际的预期是上面的<code>box</code>应该在<code>canvas</code>对象下面，而下面的<code>box</code>应该在<code>canvas</code>对象上面，模拟器上的效果始终是<code>canvas</code>对象在最上层。</p>
<p><a target="_blank" rel="noopener" href="https://developers.weixin.qq.com/s/9dvrEDmN7jzY">小程序代码片段</a></p>
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