Activity生命周期（二）

上一篇（http://blog.csdn.net/niuzhucedenglu/article/details/50910369）通过覆写Activity的方法来查看Activity的生命周期，
这里对上一篇进行补充一下，看官方文档怎么说的^_^

onCreate

/**
     * Called when the activity is starting.  This is where most initialization
     * should go: calling {@link #setContentView(int)} to inflate the
     * activity's UI, using {@link #findViewById} to programmatically interact
     * with widgets in the UI, calling
     * {@link #managedQuery(android.net.Uri , String[], String, String[], String)} to retrieve
     * cursors for data being displayed, etc.
     *
     * <p>You can call {@link #finish} from within this function, in
     * which case onDestroy() will be immediately called without any of the rest
     * of the activity lifecycle ({@link #onStart}, {@link #onResume},
     * {@link #onPause}, etc) executing.
     *
     * <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>
     *
     * @param savedInstanceState If the activity is being re-initialized after
     *     previously being shut down then this Bundle contains the data it most
     *     recently supplied in {@link #onSaveInstanceState}. <b><i>Note: Otherwise it is null.</i></b>
     *
     * @see #onStart
     * @see #onSaveInstanceState
     * @see #onRestoreInstanceState
     * @see #onPostCreate
     */

onRestart

/**
     * Called after {@link #onStop} when the current activity is being
     * re-displayed to the user (the user has navigated back to it).  It will
     * be followed by {@link #onStart} and then {@link #onResume}.
     *
     * <p>For activities that are using raw {@link Cursor} objects (instead of
     * creating them through
     * {@link #managedQuery(android.net.Uri , String[], String, String[], String)},
     * this is usually the place
     * where the cursor should be requeried (because you had deactivated it in
     * {@link #onStop}.
     *
     * <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 #onStop
     * @see #onStart
     * @see #onResume
     */

onStart

/**
     * Called after {@link #onCreate} — or after {@link #onRestart} when
     * the activity had been stopped, but is now again being displayed to the
     * user.  It will be followed by {@link #onResume}.
     *
     * <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 #onCreate
     * @see #onStop
     * @see #onResume
     */

onRestoreInstanceState

/**
     * This method is called after {@link #onStart} when the activity is
     * being re-initialized from a previously saved state, given here in
     * <var>savedInstanceState</var>.  Most implementations will simply use {@link #onCreate}
     * to restore their state, but it is sometimes convenient to do it here
     * after all of the initialization has been done or to allow subclasses to
     * decide whether to use your default implementation.  The default
     * implementation of this method performs a restore of any view state that
     * had previously been frozen by {@link #onSaveInstanceState}.
     *
     * <p>This method is called between {@link #onStart} and
     * {@link #onPostCreate}.
     *
     * @param savedInstanceState the data most recently supplied in {@link #onSaveInstanceState}.
     *
     * @see #onCreate
     * @see #onPostCreate
     * @see #onResume
     * @see #onSaveInstanceState
     */

onResume

/**
     * Called after {@link #onRestoreInstanceState}, {@link #onRestart}, or
     * {@link #onPause}, for your activity to start interacting with the user.
     * This is a good place to begin animations, open exclusive-access devices
     * (such as the camera), etc.
     *
     * <p>Keep in mind that onResume is not the best indicator that your activity
     * is visible to the user; a system window such as the keyguard may be in
     * front.  Use {@link #onWindowFocusChanged} to know for certain that your
     * activity is visible to the user (for example, to resume a game).
     *
     * <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 #onRestoreInstanceState
     * @see #onRestart
     * @see #onPostResume
     * @see #onPause
     */

onPause

/**
     * Called as part of the activity lifecycle when an activity is going into
     * the background, but has not (yet) been killed.  The counterpart to
     * {@link #onResume}.
     *
     * <p>When activity B is launched in front of activity A, this callback will
     * be invoked on A.  B will not be created until A's {@link #onPause} returns,
     * so be sure to not do anything lengthy here.
     *
     * <p>This callback is mostly used for saving any persistent state the
     * activity is editing, to present a "edit in place" model to the user and
     * making sure nothing is lost if there are not enough resources to start
     * the new activity without first killing this one.  This is also a good
     * place to do things like stop animations and other things that consume a
     * noticeable amount of CPU in order to make the switch to the next activity
     * as fast as possible, or to close resources that are exclusive access
     * such as the camera.
     *
     * <p>In situations where the system needs more memory it may kill paused
     * processes to reclaim resources.  Because of this, you should be sure
     * that all of your state is saved by the time you return from
     * this function.  In general {@link #onSaveInstanceState} is used to save
     * per-instance state in the activity and this method is used to store
     * global persistent data (in content providers, files, etc.)
     *
     * <p>After receiving this call you will usually receive a following call
     * to {@link #onStop} (after the next activity has been resumed and
     * displayed), however in some cases there will be a direct call back to
     * {@link #onResume} without going through the stopped state.
     *
     * <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 #onResume
     * @see #onSaveInstanceState
     * @see #onStop
     */

onSaveInstanceState

/**
     * Called to retrieve per-instance state from an activity before being killed
     * so that the state can be restored in {@link #onCreate} or
     * {@link #onRestoreInstanceState} (the {@link Bundle} populated by this method
     * will be passed to both).
     *
     * <p>This method is called before an activity may be killed so that when it
     * comes back some time in the future it can restore its state.  For example,
     * if activity B is launched in front of activity A, and at some point activity
     * A is killed to reclaim resources, activity A will have a chance to save the
     * current state of its user interface via this method so that when the user
     * returns to activity A, the state of the user interface can be restored
     * via {@link #onCreate} or {@link #onRestoreInstanceState}.
     *
     * <p>Do not confuse this method with activity lifecycle callbacks such as
     * {@link #onPause}, which is always called when an activity is being placed
     * in the background or on its way to destruction, or {@link #onStop} which
     * is called before destruction.  One example of when {@link #onPause} and
     * {@link #onStop} is called and not this method is when a user navigates back
     * from activity B to activity A: there is no need to call {@link #onSaveInstanceState}
     * on B because that particular instance will never be restored, so the
     * system avoids calling it.  An example when {@link #onPause} is called and
     * not {@link #onSaveInstanceState} is when activity B is launched in front of activity A:
     * the system may avoid calling {@link #onSaveInstanceState} on activity A if it isn't
     * killed during the lifetime of B since the state of the user interface of
     * A will stay intact.
     *
     * <p>The default implementation takes care of most of the UI per-instance
     * state for you by calling {@link android.view.View#onSaveInstanceState()} on each
     * view in the hierarchy that has an id, and by saving the id of the currently
     * focused view (all of which is restored by the default implementation of
     * {@link #onRestoreInstanceState}). If you override this method to save additional
     * information not captured by each individual view, you will likely want to
     * call through to the default implementation, otherwise be prepared to save
     * all of the state of each view yourself.
     *
     * <p>If called, this method will occur before {@link #onStop}. There are
     * no guarantees about whether it will occur before or after {@link #onPause}.
     *
     * @param outState Bundle in which to place your saved state.
     *
     * @see #onCreate
     * @see #onRestoreInstanceState
     * @see #onPause
     */

onStop

/**
     * 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.
     *
     * <p>Note that this method may never be called, in low memory situations
     * where the system does not have enough memory to keep your activity's
     * process running after its {@link #onPause} method is called.
     *
     * <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
     */

onDestroy

/**
     * Perform any final cleanup before an activity is destroyed.  This can
     * happen either because the activity is finishing (someone called
     * {@link #finish} on it, or because the system is temporarily destroying
     * this instance of the activity to save space.  You can distinguish
     * between these two scenarios with the {@link #isFinishing} method.
     *
     * <p><em>Note: do not count on this method being called as a place for
     * saving data! For example, if an activity is editing data in a content
     * provider, those edits should be committed in either {@link #onPause} or
     * {@link #onSaveInstanceState}, not here.</em> This method is usually implemented to
     * free resources like threads that are associated with an activity, so
     * that a destroyed activity does not leave such things around while the
     * rest of its application is still running.  There are situations where
     * the system will simply kill the activity's hosting process without
     * calling this method (or any others) in it, so it should not be used to
     * do things that are intended to remain around after the process goes
     * away.
     *
     * <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 #onPause
     * @see #onStop
     * @see #finish
     * @see #isFinishing
     */