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framework.functions.class.html
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<h1 class="sectionedit1" id="class_高级用法">class() 高级用法</h1>
<div class="level1">
<p>
class() 除了定义纯 Lua 类之外，还可以从 C++ 对象继承类。
</p>
<p>
比如需要创建一个工具栏，并在添加按钮时自动排列已有的按钮，那么我们可以使用如下的代码：
</p>
<pre class="code lua"><span class="co1">-- 从 CCNode 对象派生 Toolbar 类，该类具有 CCNode 的所有属性和行为</span>
<span class="kw1">local</span> Toolbar <span class="sy0">=</span> class<span class="br0">(</span><span class="st0">"Toolbar"</span><span class="sy0">,</span> <span class="kw1">function</span><span class="br0">(</span><span class="br0">)</span>
<span class="kw1">return</span> display<span class="sy0">.</span>newNode<span class="br0">(</span><span class="br0">)</span> <span class="co1">-- 返回一个 CCNode 对象</span>
<span class="kw1">end</span><span class="br0">)</span>
<span class="co1">-- 构造函数</span>
<span class="kw1">function</span> Toolbar<span class="sy0">:</span>ctor<span class="br0">(</span><span class="br0">)</span>
self<span class="sy0">.</span>buttons <span class="sy0">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">-- 用一个 table 来记录所有的按钮</span>
<span class="kw1">end</span>
<span class="co1">-- 添加一个按钮，并且自动设置按钮位置</span>
<span class="kw1">function</span> Toolbar<span class="sy0">:</span>addButton<span class="br0">(</span>button<span class="br0">)</span>
<span class="co1">-- 将按钮对象加入 table</span>
self<span class="sy0">.</span>buttons<span class="br0">[</span><span class="sy0">#</span>self<span class="sy0">.</span>buttons <span class="sy0">+</span> <span class="nu0">1</span><span class="br0">]</span> <span class="sy0">=</span> button
<span class="co1">-- 添加按钮对象到 CCNode 中，以便显示该按钮</span>
<span class="co1">-- 因为 Toolbar 是从 CCNode 继承的，所以可以使用 addChild() 方法</span>
self<span class="sy0">:</span>addChild<span class="br0">(</span>button<span class="br0">)</span>
<span class="co1">-- 按照按钮数量，调整所有按钮的位置</span>
<span class="kw1">local</span> x <span class="sy0">=</span> <span class="nu0">0</span>
<span class="kw1">for</span> _<span class="sy0">,</span> button <span class="kw2">in</span> <span class="kw3">ipairs</span><span class="br0">(</span>self<span class="sy0">.</span>buttons<span class="br0">)</span> <span class="kw1">do</span>
button<span class="sy0">:</span>setPosition<span class="br0">(</span>x<span class="sy0">,</span> <span class="nu0">0</span><span class="br0">)</span>
<span class="co1">-- 依次排列按钮，每个按钮之间间隔 10 点</span>
x <span class="sy0">=</span> x <span class="sy0">+</span> button<span class="sy0">:</span>getContentSize<span class="br0">(</span><span class="br0">)</span><span class="sy0">.</span>width <span class="sy0">+</span> <span class="nu0">10</span>
<span class="kw1">end</span>
<span class="kw1">end</span></pre>
<p>
class() 的这种用法让我们可以在 C++ 对象基础上任意扩展行为。
</p>
<p>
~
</p>
<p>
既然是继承，自然就可以覆盖 C++ 对象的方法：
</p>
<pre class="code lua">
<span class="kw1">function</span> Toolbar<span class="sy0">:</span>setPosition<span class="br0">(</span>x<span class="sy0">,</span> y<span class="br0">)</span>
<span class="co1">-- 由于在 Toolbar 继承类中覆盖了 CCNode 对象的 setPosition() 方法</span>
<span class="co1">-- 所以我们要用以下形式才能调用到 CCNode 原本的 setPosition() 方法</span>
<span class="kw3">getmetatable</span><span class="br0">(</span>self<span class="br0">)</span><span class="sy0">.</span>setPosition<span class="br0">(</span>self<span class="sy0">,</span> x<span class="sy0">,</span> y<span class="br0">)</span>
printf<span class="br0">(</span><span class="st0">"x = %0.2f, y = %0.2f"</span><span class="sy0">,</span> x<span class="sy0">,</span> y<span class="br0">)</span>
<span class="kw1">end</span></pre>
<p>
<strong>注意：</strong> Lua 继承类覆盖的方法并不能从 C++ 调用到。也就是说通过 C++ 代码调用这个 CCNode 对象的 setPosition() 方法时，并不会执行我们在 Lua 中定义的 Toolbar:setPosition() 方法。
</p>
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<div class="docInfo">zh_cn/api/framework.functions/class.txt · Last modified: 2013/08/16 02:41 by Yu Lei Liao</div>
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