Activity生命周期中三个不常用的方法：onContentChanged，onPostCreate，onPostResume

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关于Activity的生命周期网上也有很多文章，最经典的莫过于官方的一张图解了。

这张图列出了Activity生命周期最主要的一些方法，启动后依次执行：

onCreate –> onStart –> onResume –> onPause –> onStop –> onDestroy

相信很多人也都已经知道以上方法与执行顺序，但是Activity还有其他方法，如onContentChanged， onPostCreate， onPostResume， onConfigurationChanged， onSaveInstanceState， onRestoreInstanceState，没有什么比自己做个Demo亲自试验研究下更有说服力了，下面我做了一个Demo来彻底研究下这些生命周期的方法，建议大家也亲自试验下：

public class DemoActivity extends Activity {

<span class="n" style="">static</span> <span class="n" style="">final</span> <span class="no" style="">String</span> <span class="no" style="">TAG</span> <span class="o" style="">=</span> <span class="no" style="">DemoActivity</span><span class="p" style="">.</span><span class="nf" style="">class</span><span class="p" style="">.</span><span class="nf" style="">getSimpleName</span><span class="p" style="">();</span>

<span class="vi" style="">@Override</span>
<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onCreate</span><span class="p" style="">(</span><span class="no" style="">Bundle</span> <span class="n" style="">savedInstanceState</span><span class="p" style="">)</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onCreate</span><span class="p" style="">(</span><span class="n" style="">savedInstanceState</span><span class="p" style="">);</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onCreate&quot;</span><span class="p" style="">);</span>
    <span class="n" style="">setContentView</span><span class="p" style="">(</span><span class="no" style="">R</span><span class="p" style="">.</span><span class="nf" style="">layout</span><span class="p" style="">.</span><span class="nf" style="">activity_demo</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="vi" style="">@Override</span>
<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onContentChanged</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onContentChanged</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onContentChanged&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onStart</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onStart</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onStart&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onRestart</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onRestart</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onRestart&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onPostCreate</span><span class="p" style="">(</span><span class="no" style="">Bundle</span> <span class="n" style="">savedInstanceState</span><span class="p" style="">)</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onPostCreate</span><span class="p" style="">(</span><span class="n" style="">savedInstanceState</span><span class="p" style="">);</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onPostCreate&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="vi" style="">@Override</span>
<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onResume</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onResume</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onResume&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onPostResume</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onPostResume</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onPostResume&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onPause</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onPause</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onPause&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onStop</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onStop</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onStop&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onDestroy</span><span class="p" style="">()</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onDestroy</span><span class="p" style="">();</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onDestroy&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onConfigurationChanged</span><span class="p" style="">(</span><span class="no" style="">Configuration</span> <span class="n" style="">newConfig</span><span class="p" style="">)</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onConfigurationChanged</span><span class="p" style="">(</span><span class="n" style="">newConfig</span><span class="p" style="">);</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onConfigurationChanged&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onSaveInstanceState</span><span class="p" style="">(</span><span class="no" style="">Bundle</span> <span class="n" style="">outState</span><span class="p" style="">)</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onSaveInstanceState</span><span class="p" style="">(</span><span class="n" style="">outState</span><span class="p" style="">);</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onSaveInstanceState&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

<span class="kp" style="">public</span> <span class="n" style="">void</span> <span class="n" style="">onRestoreInstanceState</span><span class="p" style="">(</span><span class="no" style="">Bundle</span> <span class="n" style="">outState</span><span class="p" style="">)</span> <span class="p" style="">{</span>
    <span class="k" style="">super</span><span class="p" style="">.</span><span class="nf" style="">onRestoreInstanceState</span><span class="p" style="">(</span><span class="n" style="">outState</span><span class="p" style="">);</span>
    <span class="no" style="">Log</span><span class="p" style="">.</span><span class="nf" style="">d</span><span class="p" style="">(</span><span class="no" style="">TAG</span><span class="p" style="">,</span> <span class="s2" style="">&quot;onRestoreInstanceState&quot;</span><span class="p" style="">);</span>
<span class="p" style="">}</span>

}

程序启动运行并结束上述生命周期的方法执行顺序是这样的：

onCreate –> onContentChanged –> onStart –> onPostCreate –> onResume –> onPostResume –> onPause –> onStop –> onDestroy

onContentChanged

onContentChanged()是Activity中的一个回调方法当Activity的布局改动时，即setContentView()或者addContentView()方法执行完毕时就会调用该方法，例如，Activity中各种View的findViewById()方法都可以放到该方法中。

onPostCreate、onPostResume

onPostCreate方法是指onCreate方法彻底执行完毕的回调，onPostResume类似，这两个方法官方说法是一般不会重写，现在知道的做法也就只有在使用ActionBarDrawerToggle的使用在onPostCreate需要在屏幕旋转时候等同步下状态，Google官方提供的一些实例就是如下做法：

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);

<span class="sr" style="">//</span> <span class="no" style="">Sync</span> <span class="n" style="">the</span> <span class="n" style="">toggle</span> <span class="n" style="">state</span> <span class="n" style="">after</span> <span class="n" style="">onRestoreInstanceState</span> <span class="n" style="">has</span> <span class="n" style="">occurred</span><span class="p" style="">.</span>
<span class="nf" style="">mDrawerToggle</span><span class="p" style="">.</span><span class="nf" style="">syncState</span><span class="p" style="">();</span>

}

onPause、 onStop

这里顺便再提一下onPause、 onStop的区别， onPause是在整个窗口被半遮盖或者半透明的时候会执行，而onStop则是在整个窗口被完全遮盖才会触发，触发onStop的方法之前必定会触发onPause方法。

onCreate、 onStart

onCreate方法会在第一次创建的时候执行，紧接着便会执行onStart方法，之后页面被完全遮挡会执行onStop方法，再返回的时候一般便会执行onRestart –> onStart方法，但是如果如果这时候App内存不够需要更多的内存的时候，App便会杀死该进程，结束掉该Activity，所以这时候再返回的时候便会重新执行onCreate –> onStart –> onResume方法。