Android开发——回调（Callback）
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<div><h4>1. 回调函数的定义：</h4></div>
<div>在A类中定义了一个方法，这个方法中用到了一个接口和该接口中的抽象方法，但是抽象方法没有具体的实现，需要B类去实现，B类实现该方法后，它本身不会去调用该方法，而是传递给A类，供A类去调用。</div>
<div><h4> 类比：</h4></div>
<div>你（B类）去书店买书，结果发现想买的书卖完了，这时候书店（A类）告诉你他们有来书通知业务（接口和接口中的抽象方法），于是你留下了自己的手机号让书店有书了给你来电（实现该抽象方法），书店等到有书了以后会根据你留下的电话和方法给你来电提醒你（B类实现的方法由A类来调用）。</div>
<div><h4>2. 使用回调的情况：</h4></div>
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<ul><li>处理异步请求的返回值</li><li>同一个事件有不同的处理方法</li></ul></div>
<div><h4>3. 回调的使用方法：</h4></div>
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<ul><li>定义接口(public interfact)，预定义需要完成的函数</li><li>定义A类，使用接口和该接口中的抽象方法，同时在初始化A时请求函数B作为callback的参数</li><li>定义B类(implements interface)，设定函数的具体动作，并将B当做参数传给A，使A在回调时可以找到函数的位置</li></ul></div>
<div><h4>4. 具体代码：</h4></div>
<div>
<ul><li><span>定义接口</span></li></ul><span><span></span></span><pre><code class="language-java hljs"></code><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">//定义回调接口</span><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">Callback</span></span>{</div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">notice</span><span class="hljs-params">()</span></span>;<div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div><div class="hljs-button {2}"></div></div></div></div></div></pre>
<ul><li><span>定义A类</span><span></span><pre><code class="language-java hljs"></code><div class="hljs-ln-numbers"><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span></span>{<div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">private</span> CallBack callBack;<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-title">A</span><span class="hljs-params">(CallBack callBack)</span></span>{<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">this</span>.callBack = callBack;<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }</div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">Operation</span><span class="hljs-params">()</span></span>{<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">if</span>(callBack != <span class="hljs-keyword">null</span>){<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> callBack.notice();<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }<div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div><div class="hljs-button {2}"></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></pre></li><li><span>定义B类</span></li></ul><span></span><pre><code class="language-java hljs"></code><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span> <span class="hljs-title">implement</span> <span class="hljs-title">CallBack</span></span>{</div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String args[])</span> </span>{ </div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> A a = <span class="hljs-keyword">new</span> A(<span class="hljs-keyword">this</span>);</div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> a.Operation();</div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> } <div class="hljs-ln-code"><div class="hljs-ln-line"> </div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-meta">@Override</span></span></div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">notice</span><span class="hljs-params">()</span></span>{</div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"Now you get notice!"</span>);</div></div><div class="hljs-ln-numbers"></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }</div></div><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></div></div></div></pre><br><br><br></div> </div><br><br>
来源：https://www.cnblogs.com/JasonLGJnote/p/11159861.html
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