开启掘金成长之旅！这是我参与「掘金日新计划 · 2 月更文挑战」的第 5 天，点击查看活动详情
当A Activity启动B Activity后，其生命周期如何变化呢？我们沿用前文中Hook Instrumentation的方案来看下，在Activity互相跳转时，其生命周期如何变化，修改MyCustomInstrumentation，如下所示：
public class CustomInstrumentation extends Instrumentation {
private static final String TAG = "CustomInstrumentation";
private Instrumentation mBaseInstrumentation;
public CustomInstrumentation(Instrumentation instrumentation) {
super();
mBaseInstrumentation = instrumentation;
}
@Override
public void callActivityOnCreate(Activity activity, Bundle icicle) {
super.callActivityOnCreate(activity, icicle);
Log.d(TAG, "callActivityOnCreate " + activity.toString());
}
@Override
public void callActivityOnStart(Activity activity) {
super.callActivityOnStart(activity);
Log.d(TAG, "callActivityOnStart " + activity.toString());
}
@Override
public void callActivityOnResume(Activity activity) {
super.callActivityOnResume(activity);
Log.d(TAG, "callActivityOnResume " + activity.toString());
}
@Override
public void callActivityOnPause(Activity activity) {
super.callActivityOnPause(activity);
Log.d(TAG, "callActivityOnPause " + activity.toString());
}
@Override
public void callActivityOnStop(Activity activity) {
super.callActivityOnStop(activity);
Log.d(TAG, "callActivityOnStop " + activity.toString());
}
@Override
public void callActivityOnDestroy(Activity activity) {
super.callActivityOnDestroy(activity);
Log.d(TAG, "callActivityOnDestroy " + activity.toString());
}
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
Log.d(TAG, "newActivity: " + className);
return mBaseInstrumentation.newActivity(cl, className, intent);
}
}
启动普通的Activity
在MainActivity中以startActivity方式启动NotifyAcLifecycleActivity，启动后不finish MainActivity，此时CustomInstrumentation打印的日志如下：
从日志可以看出当MainActivity启动NotifyAcLifecycleActivity时，生命周期变化如下图所示：
启动Dialog样式或者Translucent的Activity
新建DialogActivity，指定其Theme为Theme.AppCompat.Dialog，随后在MainActivity中启动DialogActivity，此时CustomInstrumentation打印的日志如下：
可以看出，当DialogActivity onResume执行后，MainActivity并没有执行onStop方法，仍然处于pause状态，进而我们可以总结出：
- A Activity启动非Dialog样式的Activity后，A先pause，随后B进入resume状态后，A调用onStop
- A Activity启动Dialog样式的Activity后，A先pause，随后B进入resume状态
从上述结论，我们不难推断onStop设计的意图是当Activity对用户完全不可见时回调，接下来我们来看下源码中onStop的说明：
/**
* Called when you are no longer visible to the user. You will next
* receive either {@link #onRestart}, {@link #onDestroy}, or nothing,
* depending on later user activity. This is a good place to stop
* refreshing UI, running animations and other visual things.
*
* <p><em>Derived classes must call through to the super class's
* implementation of this method. If they do not, an exception will be
* thrown.</em></p>
*
* @see #onRestart
* @see #onResume
* @see #onSaveInstanceState
* @see #onDestroy
*/
@CallSuper
protected void onStop() {
......
}
从其方法注释上也能看到该说明，onStop method Called when you are no longer visible to the user. 同样的我们也可以看到onPause的函数说明中关于其调用时机的介绍，当当前页面不再参与用户交互时，会回调该方法，Called as part of the activity lifecycle when the user no longer actively interacts with the activity, but it is still visible on screen. The counterpart to onResume.
重新梳理Activity各声明周期函数回调时机如下图所示：
在onCreate中直接调用finish，会出现onCreate，onResume，onDestroy序列的生命周期现象
