Android Activity启动流程源码解析

在 Android Launcher启动应用程序流程源码解析一文中从点击应用程序图标

startActivity()

开始，一直讲解到

Application

和

MainActivity

的

onCreate()

方法被调用。中间流程有些高能，高能部分是两篇博文共有的地方，没办法绕开。本文主要讲述从

Activity#onCreate()

到

Activity#onResume()

的流程。想追本溯源的同学建议先阅读 Android
Launcher启动应用程序流程源码解析之后，再回头读这篇博文。不啰嗦了，Here we Go~

无论显式还是隐式启动

Activity

，都会进入到

ActivityThread#handleLaunchActivity()

源码位置：frameworks/base/core/Java/Android/app/ActivityThread.java

ActivityThread#handleLaunchActivity()

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
......
// 加载activity,然后调用onCreate,onStart方法
Activity a = performLaunchActivity(r, customIntent);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (a != null) {
// 调用onResume方法
handleResumeActivity(r.token, false, r.isForward, !r.activity.mFinished && !r.startsNotResumed);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}  </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li></ul>

注释有点剧透，，今天的重点全在这个方法里。首先看下

performLaunchActivity()

ActivityThread#performLaunchActivity()

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
Activity activity = null;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (activity != null) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
activity.attach(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>)
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> activity;
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">24</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">25</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">26</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">27</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">28</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">29</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">24</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">25</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">26</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">27</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">28</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">29</span></li></ul>

mInstrumentation.callActivityOnCreate

这行代码的作用就是调用

Activity#onCreate()

，在 Android
Launcher启动应用程序流程源码解析已经介绍过，这里就不再赘述了。直接看

activity.performStart()

，这个方法的名字十分吸引人呐～跟进。

源码位置：frameworks/base/core/java/android/app/Activity.java

Activity#performStart()

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> performStart() {
mActivityTransitionState.setEnterActivityOptions(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, getActivityOptions());
mFragments.noteStateNotSaved();
mCalled = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
mFragments.execPendingActions();
mInstrumentation.callActivityOnStart(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!mCalled) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SuperNotCalledException(
<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Activity "</span> + mComponent.toShortString() +
<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" did not call through to super.onStart()"</span>);
}
mFragments.dispatchStart();
mFragments.reportLoaderStart();
mActivityTransitionState.enterReady(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>);
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">15</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">15</span></li></ul>

真相已经呼之欲出了～，跟进。

源码位置：frameworks/base/core/java/android/app/Instrumentation.java

Instrumentation#callActivityOnStart()

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">callActivityOnStart</span>(Activity activity) {
activity.onStart();
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li></ul>

哈哈～又找到一个方法

Activity#onStart()

。真是轻而易举～

现在回到

ActivityThread#performLaunchActivity()

中的

handleResumeActivity(r.token,
false, r.isForward, !r.activity.mFinished && !r.startsNotResumed)

，跟进。

源码位置：frameworks/base/core/java/android/app/ActivityThread.java

ActivityThread#handleResumeActivity()

ActivityThread#ActivityClientRecord()

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">   final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
ActivityClientRecord r = performResumeActivity(token, clearHide);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}

public final ActivityClientRecord performResumeActivity(IBinder token,
boolean clearHide) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
r.activity.performResume();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li></ul>

中间都是各种状态效验，没撒好说的。直接跟进。

源码位置：frameworks/base/core/java/android/app/Activity.java

Activity#performResume()

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    final void performResume() {
performRestart();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
mInstrumentation.callActivityOnResume(this);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li></ul>

在这里有两个分支

1. 在执行

onResume()

前需要先执行

onRestart()

和

onStart()

。例如从上个

Activity

返回的时候，这里不作为重点，但也会稍微看下。

2. 直接执行

onResume()

分支1：

Activity#performRestart()

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    final void performRestart() {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
mInstrumentation.callActivityOnRestart(this);
performStart();
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li></ul>

这两个方法在上文都分析过了，不再赘述。

分支2：

源码位置：frameworks/base/core/java/android/app/Instrumentation.java

Instrumentation#callActivityOnStart()

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span style="font-size:18px;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">callActivityOnResume</span>(Activity activity) {
activity.mResumed = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
activity.onResume();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mActivityMonitors != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> (mSync) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> N = mActivityMonitors.size();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i<N; i++) {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> ActivityMonitor am = mActivityMonitors.get(i);
am.match(activity, activity, activity.getIntent());
}
}
}
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-size:18px;">14</span></li></ul>

直接调用

Activity#OnResume()

。

结束了。这篇博客结束的比之前任何一篇博文都要快，都要好理解。这一切的前提是已经阅读过我原来的博文 Android Launcher启动应用程序流程源码解析。
http://blog.csdn.net/qq_17250009/article/details/52816169