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capture-screenshot-event-on-android.html
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<h1 class="post-title">捕获Android截屏事件</h1>
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<time class="post-date" datetime="2017-08-02">02 Aug 2017</time>
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<p>在Android平台上截屏事件没有对应的一个标准的事件和通知，所以应用App无法通过标准或统一的方式去捕获这个事件来满足自己的要求。
只能通过间接的方式捕获到这个事件，我因为要做一个微信的截屏图片分享的功能，所以对Android截屏事件做了一个调研，并且在开发中
选用了其中的一种方式。 大体上，要解决这个问题，大概有以下几种方法，每种方法的可靠性和灵活性都不同。</p>
<h4 id="通过按键监听捕获截屏事件">通过按键监听捕获截屏事件</h4>
<p>这种方式最简单粗暴，但是存在两个巨大的麻烦，不易克服:</p>
<ul>
<li>
<p>Android机器厂商众多，ROM众多，多截屏按键的组合没有统一的标准，如果适配所有机型，几乎是无法完成的任务</p>
</li>
<li>
<p>事件准确捕获后，截屏这个动作完全结束时点需要应用自己去检查和获取</p>
</li>
</ul>
<p>这两件事做起来都不容易，都很容易出错，所以这种方法基本上是四种办法里最不可靠的，基本不推荐这么做。</p>
<h4 id="通过监听系统截屏进程的运行和退出捕获截屏事件">通过监听系统截屏进程的运行和退出捕获截屏事件</h4>
<p>这种方法需要有一个后台线程以一定的频率去检查系统截屏进程是否启动，运行，退出，并作出相应的逻辑，而这个频率其实很难把握，毕竟应用无法预期这个截屏动作，因此这种方法也不推荐，此种方法和上面的那种方法可能只适用于非常特定的场景。</p>
<h4 id="通过fileobserver间接捕获">通过FileObserver间接捕获</h4>
<p>这种方法其实是比较可靠和可控的，就是有一个问题, 一个FileObserver初始化的时候就得决定observe哪个目录，所以适配不同机型的过程就变成了适配所以可能的目录，这个是非常麻烦的事情，不过FileObserver总体来看是可以解决这个问题的，唯一比较难的就是要适配所有可能的机型对应的目录。最开始做这个功能的时候我实现了一版使用FileObserver的实现:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ScreenshotObserver</span> <span class="kd">extends</span> <span class="nc">FileObserver</span> <span class="o">{</span>
<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="nc">String</span> <span class="no">TAG</span> <span class="o">=</span> <span class="nc">ScreenshotObserver</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getSimpleName</span><span class="o">();</span>
<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="nc">String</span> <span class="no">PATH</span> <span class="o">=</span> <span class="nc">Environment</span><span class="o">.</span><span class="na">getExternalStorageDirectory</span><span class="o">().</span><span class="na">toString</span><span class="o">()</span> <span class="o">+</span> <span class="s">"/Pictures/Screenshots/"</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">OnScreenshotTakenListener</span> <span class="n">mListener</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">String</span> <span class="n">mLastTakenPath</span><span class="o">;</span>
<span class="kd">public</span> <span class="nf">ScreenshotObserver</span><span class="o">(</span><span class="nc">OnScreenshotTakenListener</span> <span class="n">listener</span><span class="o">)</span> <span class="o">{</span>
<span class="kd">super</span><span class="o">(</span><span class="no">PATH</span><span class="o">,</span> <span class="nc">FileObserver</span><span class="o">.</span><span class="na">CLOSE_WRITE</span><span class="o">);</span>
<span class="n">mListener</span> <span class="o">=</span> <span class="n">listener</span><span class="o">;</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">onEvent</span><span class="o">(</span><span class="kt">int</span> <span class="n">event</span><span class="o">,</span> <span class="nc">String</span> <span class="n">path</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">path</span><span class="o">==</span><span class="kc">null</span> <span class="o">||</span> <span class="n">event</span><span class="o">!=</span><span class="nc">FileObserver</span><span class="o">.</span><span class="na">CLOSE_WRITE</span><span class="o">)</span>
<span class="nc">Log</span><span class="o">.</span><span class="na">d</span><span class="o">(</span><span class="no">TAG</span><span class="o">,</span> <span class="s">"Don't care."</span><span class="o">);</span>
<span class="k">else</span> <span class="nf">if</span> <span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">!=</span><span class="kc">null</span> <span class="o">&&</span> <span class="n">path</span><span class="o">.</span><span class="na">equalsIgnoreCase</span><span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">))</span>
<span class="nc">Log</span><span class="o">.</span><span class="na">d</span><span class="o">(</span><span class="no">TAG</span><span class="o">,</span> <span class="s">"This event has been observed before."</span><span class="o">);</span>
<span class="k">else</span> <span class="o">{</span>
<span class="n">mLastTakenPath</span> <span class="o">=</span> <span class="n">path</span><span class="o">;</span>
<span class="nc">File</span> <span class="n">file</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">File</span><span class="o">(</span><span class="no">PATH</span><span class="o">+</span><span class="n">path</span><span class="o">);</span>
<span class="n">mListener</span><span class="o">.</span><span class="na">onScreenshotTaken</span><span class="o">(</span><span class="nc">Uri</span><span class="o">.</span><span class="na">fromFile</span><span class="o">(</span><span class="n">file</span><span class="o">));</span>
<span class="nc">Log</span><span class="o">.</span><span class="na">d</span><span class="o">(</span><span class="no">TAG</span><span class="o">,</span> <span class="s">"Send event to listener."</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<h4 id="通过contentobserver间接捕获">通过ContentObserver间接捕获</h4>
<p>这种方式算是目前最可靠，灵活性最好的方式了。实现起来先对其他几种方式要做的事也先对多一点，一下是我的实现，这个实现针对国内的一些手机做了适配，覆盖到了一些比较极端的情况:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">ScreenshotManager</span> <span class="o">{</span>
<span class="kd">private</span> <span class="nc">OnScreenshotTakenListener</span> <span class="n">mListener</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">String</span> <span class="n">mLastTakenPath</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">Context</span> <span class="n">mContext</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">Timer</span> <span class="n">mCheckImageTimer</span><span class="o">;</span>
<span class="kd">private</span> <span class="kt">int</span> <span class="n">mCount</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="cm">/**
* Internal storage observer
*/</span>
<span class="kd">private</span> <span class="nc">ScreenshotObserver</span> <span class="n">mInternalObserver</span><span class="o">;</span>
<span class="cm">/**
* External storage observer
*/</span>
<span class="kd">private</span> <span class="nc">ScreenshotObserver</span> <span class="n">mExternalObserver</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">HandlerThread</span> <span class="n">mHandlerThread</span><span class="o">;</span>
<span class="kd">private</span> <span class="nc">Handler</span> <span class="n">mContenHandler</span><span class="o">;</span>
<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="nc">String</span><span class="o">[]</span> <span class="no">MEDIA_PROJECTIONS</span> <span class="o">=</span> <span class="o">{</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATA</span><span class="o">,</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_TAKEN</span><span class="o">,</span>
<span class="o">};</span>
<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="nc">String</span><span class="o">[]</span> <span class="no">KEYWORDS</span> <span class="o">=</span> <span class="o">{</span>
<span class="s">"screenshot"</span><span class="o">,</span> <span class="s">"screen_shot"</span><span class="o">,</span> <span class="s">"screen-shot"</span><span class="o">,</span> <span class="s">"screen shot"</span><span class="o">,</span>
<span class="s">"screencapture"</span><span class="o">,</span> <span class="s">"screen_capture"</span><span class="o">,</span> <span class="s">"screen-capture"</span><span class="o">,</span> <span class="s">"screen capture"</span><span class="o">,</span>
<span class="s">"screencap"</span><span class="o">,</span> <span class="s">"screen_cap"</span><span class="o">,</span> <span class="s">"screen-cap"</span><span class="o">,</span> <span class="s">"screen cap"</span><span class="o">,</span> <span class="s">"截屏"</span>
<span class="o">};</span>
<span class="kd">public</span> <span class="nf">ScreenshotManager</span><span class="o">(</span><span class="nc">Context</span> <span class="n">context</span><span class="o">,</span> <span class="nc">OnScreenshotTakenListener</span> <span class="n">listener</span><span class="o">)</span> <span class="o">{</span>
<span class="n">mContext</span> <span class="o">=</span> <span class="n">context</span><span class="o">;</span>
<span class="n">mListener</span> <span class="o">=</span> <span class="n">listener</span><span class="o">;</span>
<span class="n">mLastTakenPath</span> <span class="o">=</span> <span class="n">getLastTakenPath</span><span class="o">();</span>
<span class="n">mHandlerThread</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">HandlerThread</span><span class="o">(</span><span class="s">"Screenshot_Observer"</span><span class="o">);</span>
<span class="n">mHandlerThread</span><span class="o">.</span><span class="na">start</span><span class="o">();</span>
<span class="n">mContenHandler</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">Handler</span><span class="o">(</span><span class="n">mHandlerThread</span><span class="o">.</span><span class="na">getLooper</span><span class="o">());</span>
<span class="n">mInternalObserver</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">ScreenshotObserver</span><span class="o">(</span><span class="n">mContenHandler</span><span class="o">,</span> <span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">INTERNAL_CONTENT_URI</span><span class="o">);</span>
<span class="n">mExternalObserver</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">ScreenshotObserver</span><span class="o">(</span><span class="n">mContenHandler</span><span class="o">,</span> <span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">EXTERNAL_CONTENT_URI</span><span class="o">);</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">startScreenshotObserver</span><span class="o">()</span> <span class="o">{</span>
<span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">registerContentObserver</span><span class="o">(</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">INTERNAL_CONTENT_URI</span><span class="o">,</span>
<span class="kc">false</span><span class="o">,</span>
<span class="n">mInternalObserver</span>
<span class="o">);</span>
<span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">registerContentObserver</span><span class="o">(</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">EXTERNAL_CONTENT_URI</span><span class="o">,</span>
<span class="kc">false</span><span class="o">,</span>
<span class="n">mExternalObserver</span>
<span class="o">);</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">stopScreenshotObserver</span><span class="o">()</span> <span class="o">{</span>
<span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">unregisterContentObserver</span><span class="o">(</span><span class="n">mInternalObserver</span><span class="o">);</span>
<span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">unregisterContentObserver</span><span class="o">(</span><span class="n">mExternalObserver</span><span class="o">);</span>
<span class="n">releaseTimer</span><span class="o">();</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kt">void</span> <span class="nf">handleMediaContentChange</span><span class="o">(</span><span class="nc">Uri</span> <span class="n">contentUri</span><span class="o">)</span> <span class="o">{</span>
<span class="nc">Cursor</span> <span class="n">cursor</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
<span class="k">try</span> <span class="o">{</span>
<span class="c1">// 数据改变时查询数据库中最后加入的一条数据</span>
<span class="n">cursor</span> <span class="o">=</span> <span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">query</span><span class="o">(</span>
<span class="n">contentUri</span><span class="o">,</span>
<span class="no">MEDIA_PROJECTIONS</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_ADDED</span> <span class="o">+</span> <span class="s">" desc limit 1"</span>
<span class="o">);</span>
<span class="k">if</span> <span class="o">(</span><span class="n">cursor</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(!</span><span class="n">cursor</span><span class="o">.</span><span class="na">moveToFirst</span><span class="o">())</span> <span class="o">{</span>
<span class="k">return</span><span class="o">;</span>
<span class="o">}</span>
<span class="c1">// 获取各列的索引</span>
<span class="kt">int</span> <span class="n">dataIndex</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATA</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">dateTakenIndex</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_TAKEN</span><span class="o">);</span>
<span class="c1">// 获取行数据</span>
<span class="nc">String</span> <span class="n">data</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getString</span><span class="o">(</span><span class="n">dataIndex</span><span class="o">);</span>
<span class="kt">long</span> <span class="n">dateTaken</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getLong</span><span class="o">(</span><span class="n">dateTakenIndex</span><span class="o">);</span>
<span class="c1">// 处理获取到的第一行数据</span>
<span class="n">handleMediaRowData</span><span class="o">(</span><span class="n">data</span><span class="o">,</span> <span class="n">dateTaken</span><span class="o">);</span>
<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="nc">Exception</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
<span class="n">e</span><span class="o">.</span><span class="na">printStackTrace</span><span class="o">();</span>
<span class="o">}</span> <span class="k">finally</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">cursor</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&&</span> <span class="o">!</span><span class="n">cursor</span><span class="o">.</span><span class="na">isClosed</span><span class="o">())</span> <span class="o">{</span>
<span class="n">cursor</span><span class="o">.</span><span class="na">close</span><span class="o">();</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kt">void</span> <span class="nf">handleMediaRowData</span><span class="o">(</span><span class="nc">String</span> <span class="n">data</span><span class="o">,</span> <span class="kt">long</span> <span class="n">dateTaken</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="nc">TextUtils</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">(</span><span class="n">data</span><span class="o">))</span>
<span class="k">return</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span><span class="n">checkScreenShot</span><span class="o">(</span><span class="n">data</span><span class="o">,</span> <span class="n">dateTaken</span><span class="o">))</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(!</span><span class="n">data</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">))</span> <span class="o">{</span>
<span class="n">mLastTakenPath</span> <span class="o">=</span> <span class="n">data</span><span class="o">;</span>
<span class="kd">final</span> <span class="nc">File</span> <span class="n">file</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">File</span><span class="o">(</span><span class="n">data</span><span class="o">);</span>
<span class="k">if</span><span class="o">(</span><span class="kc">null</span> <span class="o">==</span> <span class="nc">BitmapFactory</span><span class="o">.</span><span class="na">decodeFile</span><span class="o">(</span><span class="n">file</span><span class="o">.</span><span class="na">getPath</span><span class="o">()))</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">mCheckImageTimer</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="n">mCheckImageTimer</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">Timer</span><span class="o">();</span>
<span class="o">}</span>
<span class="n">mCheckImageTimer</span><span class="o">.</span><span class="na">schedule</span><span class="o">(</span><span class="k">new</span> <span class="nc">TimerTask</span><span class="o">()</span> <span class="o">{</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">run</span><span class="o">()</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">mCount</span> <span class="o">></span> <span class="mi">10</span><span class="o">)</span> <span class="o">{</span>
<span class="n">mCheckImageTimer</span><span class="o">.</span><span class="na">cancel</span><span class="o">();</span>
<span class="n">mCheckImageTimer</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
<span class="k">return</span><span class="o">;</span>
<span class="o">}</span>
<span class="nc">Bitmap</span> <span class="n">image</span> <span class="o">=</span> <span class="nc">BitmapFactory</span><span class="o">.</span><span class="na">decodeFile</span><span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">);</span>
<span class="k">if</span><span class="o">(</span><span class="n">image</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="n">mListener</span><span class="o">.</span><span class="na">onScreenshotTaken</span><span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">);</span>
<span class="n">mCheckImageTimer</span><span class="o">.</span><span class="na">cancel</span><span class="o">();</span>
<span class="n">mCheckImageTimer</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
<span class="n">mCount</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
<span class="n">mCount</span><span class="o">++;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">},</span> <span class="mi">0</span><span class="o">,</span> <span class="mi">1000</span><span class="o">);</span>
<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
<span class="n">mListener</span><span class="o">.</span><span class="na">onScreenshotTaken</span><span class="o">(</span><span class="n">mLastTakenPath</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="n">mLastTakenPath</span> <span class="o">=</span> <span class="n">data</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kt">boolean</span> <span class="nf">checkScreenShot</span><span class="o">(</span><span class="nc">String</span> <span class="n">data</span><span class="o">,</span> <span class="kt">long</span> <span class="n">dateTaken</span><span class="o">)</span> <span class="o">{</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="na">toLowerCase</span><span class="o">();</span>
<span class="c1">// 判断图片路径是否含有指定的关键字之一, 如果有, 则认为当前截屏了</span>
<span class="k">for</span> <span class="o">(</span><span class="nc">String</span> <span class="n">keyWork</span> <span class="o">:</span> <span class="no">KEYWORDS</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">data</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">keyWork</span><span class="o">))</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="nc">String</span> <span class="nf">getLastTakenPath</span><span class="o">()</span> <span class="o">{</span>
<span class="nc">Cursor</span> <span class="n">cursor</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
<span class="nc">String</span> <span class="n">path</span> <span class="o">=</span> <span class="s">""</span><span class="o">;</span>
<span class="k">try</span> <span class="o">{</span>
<span class="c1">// 数据改变时查询数据库中最后加入的一条数据</span>
<span class="n">cursor</span> <span class="o">=</span> <span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">query</span><span class="o">(</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">INTERNAL_CONTENT_URI</span><span class="o">,</span>
<span class="no">MEDIA_PROJECTIONS</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_ADDED</span> <span class="o">+</span> <span class="s">" desc limit 1"</span>
<span class="o">);</span>
<span class="k">if</span> <span class="o">(</span><span class="n">cursor</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="s">""</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(!</span><span class="n">cursor</span><span class="o">.</span><span class="na">moveToFirst</span><span class="o">())</span> <span class="o">{</span>
<span class="k">return</span> <span class="s">""</span><span class="o">;</span>
<span class="o">}</span>
<span class="kt">int</span> <span class="n">dataIndex</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATA</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">dateTakenIndex</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_TAKEN</span><span class="o">);</span>
<span class="n">path</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getString</span><span class="o">(</span><span class="n">dataIndex</span><span class="o">);</span>
<span class="n">cursor</span> <span class="o">=</span> <span class="n">mContext</span><span class="o">.</span><span class="na">getContentResolver</span><span class="o">().</span><span class="na">query</span><span class="o">(</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">Media</span><span class="o">.</span><span class="na">EXTERNAL_CONTENT_URI</span><span class="o">,</span>
<span class="no">MEDIA_PROJECTIONS</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="kc">null</span><span class="o">,</span>
<span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_ADDED</span> <span class="o">+</span> <span class="s">" desc limit 1"</span>
<span class="o">);</span>
<span class="k">if</span> <span class="o">(</span><span class="n">cursor</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="s">""</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(!</span><span class="n">cursor</span><span class="o">.</span><span class="na">moveToFirst</span><span class="o">())</span> <span class="o">{</span>
<span class="k">return</span> <span class="s">""</span><span class="o">;</span>
<span class="o">}</span>
<span class="n">dataIndex</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATA</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">index</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getColumnIndex</span><span class="o">(</span><span class="nc">MediaStore</span><span class="o">.</span><span class="na">Images</span><span class="o">.</span><span class="na">ImageColumns</span><span class="o">.</span><span class="na">DATE_TAKEN</span><span class="o">);</span>
<span class="k">if</span> <span class="o">(</span><span class="n">index</span> <span class="o">></span> <span class="n">dateTakenIndex</span><span class="o">)</span> <span class="o">{</span>
<span class="n">path</span> <span class="o">=</span> <span class="n">cursor</span><span class="o">.</span><span class="na">getString</span><span class="o">(</span><span class="n">dataIndex</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="nc">Exception</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
<span class="n">e</span><span class="o">.</span><span class="na">printStackTrace</span><span class="o">();</span>
<span class="o">}</span> <span class="k">finally</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">cursor</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&&</span> <span class="o">!</span><span class="n">cursor</span><span class="o">.</span><span class="na">isClosed</span><span class="o">())</span> <span class="o">{</span>
<span class="n">cursor</span><span class="o">.</span><span class="na">close</span><span class="o">();</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">path</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kt">void</span> <span class="nf">releaseTimer</span><span class="o">()</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span><span class="n">mCheckImageTimer</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
<span class="n">mCheckImageTimer</span><span class="o">.</span><span class="na">cancel</span><span class="o">();</span>
<span class="n">mCheckImageTimer</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kd">interface</span> <span class="nc">OnScreenshotTakenListener</span> <span class="o">{</span>
<span class="kt">void</span> <span class="nf">onScreenshotTaken</span><span class="o">(</span><span class="nc">String</span> <span class="n">path</span><span class="o">);</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kd">class</span> <span class="nc">ScreenshotObserver</span> <span class="kd">extends</span> <span class="nc">ContentObserver</span> <span class="o">{</span>
<span class="kd">private</span> <span class="nc">Uri</span> <span class="n">mContentUri</span><span class="o">;</span>
<span class="kd">public</span> <span class="nf">ScreenshotObserver</span><span class="o">(</span><span class="nc">Handler</span> <span class="n">handler</span><span class="o">,</span> <span class="nc">Uri</span> <span class="n">contentUri</span><span class="o">)</span> <span class="o">{</span>
<span class="kd">super</span><span class="o">(</span><span class="n">handler</span><span class="o">);</span>
<span class="n">mContentUri</span> <span class="o">=</span> <span class="n">contentUri</span><span class="o">;</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">onChange</span><span class="o">(</span><span class="kt">boolean</span> <span class="n">selfChange</span><span class="o">)</span> <span class="o">{</span>
<span class="kd">super</span><span class="o">.</span><span class="na">onChange</span><span class="o">(</span><span class="n">selfChange</span><span class="o">);</span>
<span class="n">handleMediaContentChange</span><span class="o">(</span><span class="n">mContentUri</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p>这种方式比起FileObserver有一个明显的不同，就是FileObserver得在截屏之前就得知道哪些目录需要监听，而ContentObserver则是在文件系统发生变化的时候去查特定的目录和存储位置，适配起来就相对灵活，只要枚举出这些目录即可。综上，ContentObserver应该是最优的一种实现方式。</p>
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<h2>Android开发中二维码库的选用</h2>
<p>在现今的移动App开发中，二维码的使用场景变得越来越普遍，最近我要开发的一个需求就必须生成二维码，自然就面临二维码库选用的问题，因为大名鼎鼎的ZXing的存在，这也本不是什么特别需要考虑的问题。但是因为ZXing的大而全，要在一款只是将二维码作为一个特定使用场景下的一个功能的App，完全引入ZXing就有点过了，所以就面临了ZXing库的裁剪问题。但是裁剪这样一个大而全的多平台支持的库也不是什么简单的事情，所以我也顺便调研了其他的二维码库作为参考:
* OnBarCode http://www.onbarcode.com/products/android_barcode/barcodes/qrcode.html#intro
* Barcode4j http://barcode4j.sourceforge.net/
* QRGenerator
* https://github.com/androidmads/QRGenerator
* https://androidmads.blogspot.com/2016/07/qr-code-generator-library.html
当然了，这些库实现我的需求都是没有问题的，但是最终我还是在我的项目中选用了ZXing,一来是因为它在业界的广泛使用得到了充分的验证，二来是因为我们项目组其他的同事也会在未来的需求中使用到，所以必须选用一个长期的可靠的的解决方案。当然了，我是选用了一版裁剪后的ZXing库。至于这个库的使用其实没有什么好说的，因为使用起来非常简单，简单的几个事例就能明白如何应用。
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