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<h4 id="1-何谓Handler机制？"><a href="#1-何谓Handler机制？" class="headerlink" title="1.何谓Handler机制？"></a>1.何谓Handler机制？</h4><p>一般来说，当你的应用被创建的时候，会创建一条应用的主线程。因为效率的考虑，所有的 View 和 Widget 都不是线程安全的，所以相关操作强制放在同一个线程，这样就可以避免多线程带来的问题。这个线程就是主线程，也即 UI 线程。</p>
<a id="more"></a>
<p>当然，你可以创建自己的线程去做操作，但如何应用的主线程通信呢。那就要使用到 Handler 机制了。如果你将一个 Handler 和你的 UI 线程连接，处理消息的代码就将会在 UI 线程中执行。新线程和UI线程的通信是通过从你的新线程调用和主线程相关的 Handler 对象的相关方法实现的。</p>
<p>那接下来就要介绍一下这个消息通讯机制 Handler，涉及到三个主要的类：Looper，Handler 和 Message 类。</p>
<h4 id="2-Looper"><a href="#2-Looper" class="headerlink" title="2.Looper"></a>2.Looper</h4><p>重点方法为：prepare()和loop()</p>
<h5 id="Looper-prepare-："><a href="#Looper-prepare-：" class="headerlink" title="Looper#prepare()："></a>Looper#prepare()：</h5><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> ThreadLocal sThreadLocal = <span class="keyword">new</span> ThreadLocal(); </span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">void</span> <span class="title">prepare</span><span class="params">()</span> </span>{ </span><br><span class="line"> <span class="keyword">if</span> (sThreadLocal.get() != <span class="keyword">null</span>) { </span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> RuntimeException(<span class="string">"Only one Looper may be created per thread"</span>); </span><br><span class="line"> } </span><br><span class="line"> sThreadLocal.set(<span class="keyword">new</span> Looper()); </span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>解释：首先它创建了一个ThreadLocal对象，它是一个线程内部的数据存储类，通过它可以在指定的线程中存储数据。然后在prepare方法中将looper存储在线程里面。</p>
<h5 id="Looper-Looper-："><a href="#Looper-Looper-：" class="headerlink" title="Looper#Looper()："></a>Looper#Looper()：</h5><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="title">Looper</span><span class="params">(<span class="keyword">boolean</span> quitAllowed)</span> </span>{</span><br><span class="line"> mQueue = <span class="keyword">new</span> MessageQueue(quitAllowed); </span><br><span class="line"> mRun = <span class="keyword">true</span>; </span><br><span class="line"> mThread = Thread.currentThread();</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>而在构造方法中，Looper创建了一个MessageQueue，虽然是叫queue但其实内部实现是一个单链表。</p>
<h5 id="Looper-loop-："><a href="#Looper-loop-：" class="headerlink" title="Looper#loop()："></a>Looper#loop()：</h5><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">loop</span><span class="params">()</span> </span>{ </span><br><span class="line"> <span class="keyword">final</span> Looper me = myLooper();</span><br><span class="line"> <span class="keyword">if</span> (me == <span class="keyword">null</span>) { </span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> RuntimeException(<span class="string">"No Looper; Looper.prepare() wasn't called on this thread."</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">final</span> MessageQueue queue = me.mQueue;</span><br><span class="line"> <span class="comment">// Make sure the identity of this thread is that of the local process,</span></span><br><span class="line"> <span class="comment">// and keep track of what that identity token actually is. </span></span><br><span class="line"> Binder.clearCallingIdentity();</span><br><span class="line"> <span class="keyword">final</span> <span class="keyword">long</span> ident = Binder.clearCallingIdentity();</span><br><span class="line"> <span class="keyword">for</span> (;;) {</span><br><span class="line"> Message msg = queue.next(); <span class="comment">// might block</span></span><br><span class="line"> <span class="keyword">if</span> (msg == <span class="keyword">null</span>) { </span><br><span class="line"> <span class="comment">// No message indicates that the message queue is quitting. </span></span><br><span class="line"> <span class="keyword">return</span>; </span><br><span class="line"> } </span><br><span class="line"> <span class="comment">// This must be in a local variable, in case a UI event sets the logger </span></span><br><span class="line"> Printer logging = me.mLogging; </span><br><span class="line"> <span class="keyword">if</span> (logging != <span class="keyword">null</span>) { </span><br><span class="line"> logging.println(<span class="string">">>>>> Dispatching to "</span> + msg.target + <span class="string">" "</span> + </span><br><span class="line"> msg.callback + <span class="string">": "</span> + msg.what); </span><br><span class="line"> } </span><br><span class="line"> msg.target.dispatchMessage(msg); </span><br><span class="line"> <span class="keyword">if</span> (logging != <span class="keyword">null</span>) { </span><br><span class="line"> logging.println(<span class="string">"<<<<< Finished to "</span> + msg.target + <span class="string">" "</span> + msg.callback); </span><br><span class="line"> } </span><br><span class="line"> <span class="comment">// Make sure that during the course of dispatching the </span></span><br><span class="line"> <span class="comment">// identity of the thread wasn't corrupted. </span></span><br><span class="line"> <span class="keyword">final</span> <span class="keyword">long</span> newIdent = Binder.clearCallingIdentity(); </span><br><span class="line"> <span class="keyword">if</span> (ident != newIdent) { </span><br><span class="line"> Log.wtf(TAG, <span class="string">"Thread identity changed from 0x"</span> </span><br><span class="line"> + Long.toHexString(ident) + <span class="string">" to 0x"</span> </span><br><span class="line"> + Long.toHexString(newIdent) + <span class="string">" while dispatching to "</span> </span><br><span class="line"> + msg.target.getClass().getName() + <span class="string">" "</span> </span><br><span class="line"> + msg.callback + <span class="string">" what="</span> + msg.what); </span><br><span class="line"> } </span><br><span class="line"> msg.recycle(); </span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Looper <span class="title">myLooper</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> sThreadLocal.get();</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>解释：方法直接返回了前面sThreadLocal存储的Looper实例，如果me为null则抛出异常，也就是说looper方法必须在prepare方法之后运行。拿到该looper实例中的mQueue即消息队列后进入了无限循环，不断从队列中取出一条消息，如果没有消息则阻塞。如果取得消息使用调用msg.target.dispatchMessage(msg);把消息交给msg的target的dispatchMessage方法去处理。而msg的target是什么呢？其实就是前面讲到的handler对象，最后会释放消息占据的资源。</p>
<p>Looper类总结：</p>
<ol>
<li>与当前线程绑定，保证一个线程只会有一个Looper实例，同时一个Looper实例也只有一个MessageQueue。</li>
<li>loop()方法，不断从MessageQueue中去取消息，交给message的target的dispatchMessage去处理。</li>
</ol>
<p>接下来就要讲发送消息的对象了，这个对象就是Handler。</p>
<h4 id="3-Handler"><a href="#3-Handler" class="headerlink" title="3.Handler"></a>3.Handler</h4><p>主要作用是将一个任务切换到某个指定的线程中去执行，同时为了解决在子线程中无法访问UI的矛盾。</p>
<p>所以我们首先看Handler的构造方法，看其如何与MessageQueue联系上的。</p>
<h5 id="Handler-Handler-："><a href="#Handler-Handler-：" class="headerlink" title="Handler#Handler()："></a>Handler#Handler()：</h5><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="title">Handler</span><span class="params">()</span> </span>{ </span><br><span class="line"> <span class="keyword">this</span>(<span class="keyword">null</span>, <span class="keyword">false</span>); </span><br><span class="line">} </span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="title">Handler</span><span class="params">(Callback callback, <span class="keyword">boolean</span> async)</span> </span>{ </span><br><span class="line"> <span class="keyword">if</span> (FIND_POTENTIAL_LEAKS) { </span><br><span class="line"> <span class="keyword">final</span> Class<? extends Handler> klass = getClass(); </span><br><span class="line"> <span class="keyword">if</span> ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) && </span><br><span class="line"> (klass.getModifiers() & Modifier.STATIC) == <span class="number">0</span>) { </span><br><span class="line"> Log.w(TAG, <span class="string">"The following Handler class should be static or leaks might occur: "</span> + klass.getCanonicalName()); </span><br><span class="line"> } </span><br><span class="line"> } </span><br><span class="line"> mLooper = Looper.myLooper(); </span><br><span class="line"> <span class="keyword">if</span> (mLooper == <span class="keyword">null</span>) { </span><br><span class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> RuntimeException(<span class="string">"Can't create handler inside thread that has not called Looper.prepare()"</span>); </span><br><span class="line"> } </span><br><span class="line"> mQueue = mLooper.mQueue; </span><br><span class="line"> mCallback = callback; </span><br><span class="line"> mAsynchronous = async; </span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>解释：在构造的时候会检查当前的Handler是否为静态类，不是静态声明的话会打印Log，提示会有内存泄漏现象的产生，然后通过Looper.myLooper()方法获取到当前线程的Looper实例（mLooper）并进一步获取到当前线程的消息队列（mQueue），这样就保证了handler的实例与我们Looper实例中MessageQueue关联上了。</p>
<p>使用的时候我们会经常使用到sendMessage方法，我们来看看源码实现：<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">sendMessage</span><span class="params">(Message msg)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> sendMessageDelayed(msg, <span class="number">0</span>);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">sendEmptyMessageDelayed</span><span class="params">(<span class="keyword">int</span> what, <span class="keyword">long</span> delayMillis)</span> </span>{</span><br><span class="line"> Message msg = Message.obtain();</span><br><span class="line"> msg.what = what;</span><br><span class="line"> <span class="keyword">return</span> sendMessageDelayed(msg, delayMillis);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">sendMessageDelayed</span><span class="params">(Message msg, <span class="keyword">long</span> delayMillis)</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (delayMillis < <span class="number">0</span>) {</span><br><span class="line"> delayMillis = <span class="number">0</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">boolean</span> <span class="title">sendMessageAtTime</span><span class="params">(Message msg, <span class="keyword">long</span> uptimeMillis)</span> </span>{</span><br><span class="line"> MessageQueue queue = mQueue;</span><br><span class="line"> <span class="keyword">if</span> (queue == <span class="keyword">null</span>) {</span><br><span class="line"> RuntimeException e = <span class="keyword">new</span> RuntimeException(</span><br><span class="line"> <span class="keyword">this</span> + <span class="string">" sendMessageAtTime() called with no mQueue"</span>);</span><br><span class="line"> Log.w(<span class="string">"Looper"</span>, e.getMessage(), e);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">false</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> enqueueMessage(queue, msg, uptimeMillis);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">boolean</span> <span class="title">enqueueMessage</span><span class="params">(MessageQueue queue, Message msg, <span class="keyword">long</span> uptimeMillis)</span> </span>{</span><br><span class="line"> msg.target = <span class="keyword">this</span>;</span><br><span class="line"> <span class="keyword">if</span> (mAsynchronous) {</span><br><span class="line"> msg.setAsynchronous(<span class="keyword">true</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> queue.enqueueMessage(msg, uptimeMillis);</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>一路跳到最后的enqueueMessage方法，enqueueMessage中首先为msg.target赋值为this，因为Looper中的loop方法会取出每个msg然后交给msg,target.dispatchMessage(msg)去处理消息，也就是把当前的handler作为msg的target属性。最终会调用queue的enqueueMessage的方法，保存到消息队列中去。</p>
<p>现在已经很清楚了Looper会调用prepare()和loop()方法，在当前执行的线程中保存一个Looper实例，这个实例会保存一个MessageQueue对象，然后当前线程进入一个无限循环中去，不断从MessageQueue中读取Handler发来的消息。然后再回调创建这个消息的handler中的dispatchMessage方法。</p>
<h5 id="Handler-dispatchMessage-："><a href="#Handler-dispatchMessage-：" class="headerlink" title="Handler#dispatchMessage()："></a>Handler#dispatchMessage()：</h5><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">dispatchMessage</span><span class="params">(Message msg)</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (msg.callback != <span class="keyword">null</span>) {</span><br><span class="line"> <span class="comment">// 如果message设置了callback，即runnable消息，处理callback！</span></span><br><span class="line"> handleCallback(msg); <span class="comment">// 并直接调用callback的run方法！</span></span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// 如果handler本身设置了callback，则执行callback </span></span><br><span class="line"> <span class="keyword">if</span> (mCallback != <span class="keyword">null</span>) {</span><br><span class="line"> <span class="keyword">if</span> (mCallback.handleMessage(msg)) {</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 如果message没有callback，则调用handler的钩子方法handleMessage</span></span><br><span class="line"> handleMessage(msg);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>几个变量和方法的解释：</p>
<ol>
<li>callback：message携带的Runnable对象，实际上就是Handler的post方法所传递的Runnable参数。</li>
</ol>
<p>我们来看一下Handler的post方法源码实现：<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">mHandler.post(<span class="keyword">new</span> Runnable() {</span><br><span class="line"> <span class="meta">@Override</span> </span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">run</span><span class="params">()</span> </span>{ </span><br><span class="line"> <span class="comment">// code</span></span><br><span class="line"> }</span><br><span class="line">});</span><br></pre></td></tr></table></figure></p>
<p>其实这个Runnable并没有创建什么线程，而是发送了一条消息：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">final</span> <span class="keyword">boolean</span> <span class="title">post</span><span class="params">(Runnable r)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> sendMessageDelayed(getPostMessage(r), <span class="number">0</span>); </span><br><span class="line">}</span><br><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">static</span> Message <span class="title">getPostMessage</span><span class="params">(Runnable r)</span> </span>{</span><br><span class="line"> Message m = Message.obtain(); </span><br><span class="line"> m.callback = r; </span><br><span class="line"> <span class="keyword">return</span> m;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>在getPostMessage中，得到了一个Message对象，然后将我们创建的Runable对象作为callback属性，赋值给了此message。</p>
<p>注意：产生一个Message对象，可以new，也可以使用Message.obtain()方法；两者都可以，但是更建议使用obtain方法，因为Message内部维护了一个Message池用于Message的复用，避免使用new重新分配内存。</p>
<ol start="2">
<li><p>mCallback：可通过Handler handler = new Handler(callback); 可以用来创建一个Handler实例但不需要派生Handler子类。它可用来拦截消息！当mCallback的handleMessage返回true的时候可以拦截消息，具体的逻辑看上面的代码很容易理解！</p>
</li>
<li><p>handleMessage(msg)：它是一个空方法，为什么呢，因为消息的最终回调是由我们控制的，我们在创建handler的时候都是复写handleMessage方法，然后根据msg.what进行消息处理。</p>
</li>
</ol>
<p>到此，这个流程已经解释完毕，总结一下：</p>
<ol>
<li>首先Looper.prepare()在本线程中保存一个Looper实例，然后该实例中保存一个MessageQueue对象；因为Looper.prepare()在一个线程中只能调用一次，所以MessageQueue在一个线程中只会存在一个。</li>
<li>Looper.loop()会让当前线程进入一个无限循环，不端从MessageQueue的实例中读取消息，然后回调msg.target.dispatchMessage(msg)方法。</li>
<li>Handler的构造方法，会首先得到当前线程中保存的Looper实例，进而与MessageQueue相关联。</li>
<li>Handler的sendMessage方法，会给msg的target赋值为handler自身，然后加入MessageQueue中。</li>
<li>在构造Handler实例时，我们会重写handleMessage方法，也就是msg.target.dispatchMessage(msg)。</li>
<li>在Activity中，我们并没有显示的调用Looper.prepare()和Looper.loop()方法，是因为在Activity的启动代码中，已经在当前UI线程调用了Looper.prepare()和Looper.loop()方法。</li>
</ol>
<p>下面是个人认为在 Activity 中一个合格的 Handler 该有的样子：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">MyHandler</span> <span class="keyword">extends</span> <span class="title">Handler</span> </span>{</span><br><span class="line"> <span class="keyword">private</span> WeakReference<CustomActivity> activityWeakReference;</span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="title">MyHandler</span><span class="params">(CustomActivity activity)</span> </span>{</span><br><span class="line"> activityWeakReference = <span class="keyword">new</span> WeakReference<CustomActivity>(activity);</span><br><span class="line"> }</span><br><span class="line"> <span class="meta">@Override</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">handleMessage</span><span class="params">(Message msg)</span> </span>{</span><br><span class="line"> CustomActivity activtiy = activityWeakReference.get();</span><br><span class="line"> <span class="keyword">if</span> (activity != <span class="keyword">null</span>) {</span><br><span class="line"> <span class="comment">// code </span></span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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