当启动activity时，相关的intent如果putExtra(EXTRA_NO_HEADERS,true),那么我们的header list就不会展示出来。同时他会搭配EXTRA_SHOW_FRAGMENT 来展示我们希望的fragment.

当启动activity时，当相关的intent包含EXTRA_SHOW_FRAGMENT就通知我们的activity去展示相关的fragment.

当使用EXTRA_SHOW_FRAGMENT 来启动我们的activity, 这个 extra能够传递一个类型为 Bundle 的对象给我们的fragment when it is 来初始化我们的PreferenceActivity.

当我们使用 EXTRA_SHOW_FRAGMENT, 这个extra 决定我们 fragment 的short title.

当我们使用 EXTRA_SHOW_FRAGMENT,这个extra 决定我们 fragment 的title.

Default value for Header.id indicating that no identifier value is set. All other values (including those below -1) are valid.

默认Header.id

Adds preferences from activities that match the given Intent.

Inflates the given XML resource and adds the preference hierarchy to the current preference hierarchy.

Finds a Preference based on its key.

Called by a preference panel fragment to finish itself.

Returns the PreferenceManager used by this activity.

Gets the root of the preference hierarchy that this activity is showing.

如果Activity当前展示的是 header list返回true  否则false.

重新加载headers，当你需要改变headers是调用.

如果你的activity使用多窗格来同事展示 the headers and a preference fragment返回true.

从你的xml文件中加载headers到list中（核心方法）

当你完善你的headers是调用（核心方法）。实现它你的activity至少有一个header item, 如果有的话你的mode就自动转为 fragment mode. 当你的activity没有headers  不要调用，那么就是之前的mode

Typical implementations will use loadHeadersFromResource(int, List) to fill in the list from a resource.

Called by startWithFragment(String, Bundle, Fragment, int, int, int) when in single-pane mode, to build an Intent to launch a new activity showing the selected fragment. The default implementation constructs an Intent that re-launches the current activity with the appropriate arguments to display the fragment.

被startWithFragment(String, Bundle, Fragment, int, int, int) 调用产生展示相关Fragment的Intent

内容改变时更新状态

Called to determine the initial header to be shown. The default implementation simply returns the fragment of the first header. Note that the returned Header object does not actually need to exist in your header list -- whatever its fragment is will simply be used to show for the initial UI.

初始化Header

Called after the header list has been updated (onBuildHeaders(List) has been called and returned due to invalidateHeaders()) to specify the header that should now be selected. The default implementation returns null to keep whatever header is currently selected.

Called when the user selects an item in the header list. The default implementation will call either startWithFragment(String, Bundle, Fragment, int, int, int) orswitchToHeader(Header) as appropriate.

Called to determine whether the header list should be hidden. The default implementation returns the value given in EXTRA_NO_HEADERS or false if it is not supplied. This is set to false, for example, when the activity is being re-launched to show a particular preference activity.

Called to determine if the activity should run in multi-pane mode. The default implementation returns true if the screen is large enough.

Called when the user has clicked on a Preference that has a fragment class name associated with it. The implementation to should instantiate and switch to an instance of the given fragment.

Set a footer that should be shown at the bottom of the header list.

Should be called after onCreate to ensure that the breadcrumbs, if any, were created. This prepends a title to the fragment breadcrumbs and attaches a listener to any clicks on the parent entry.

Sets the root of the preference hierarchy that this activity is showing.

Change the base title of the bread crumbs for the current preferences. This will normally be called for you. See FragmentBreadCrumbs for more information.

Start a new fragment.

Start a new fragment containing a preference panel. If the prefences are being displayed in multi-pane mode, the given fragment class will be instantiated and placed in the appropriate pane. If running in single-pane mode, a new activity will be launched in which to show the fragment.

Like startWithFragment(String, Bundle, Fragment, int, int, int) but uses a 0 titleRes.

Start a new instance of this activity, showing only the given preference fragment. When launched in this mode, the header list will be hidden and the given preference fragment will be instantiated and fill the entire activity.

When in two-pane mode, switch to the fragment pane to show the given preference fragment.

When in two-pane mode, switch the fragment pane to show the given preference fragment.

Called when an activity you launched exits, giving you the requestCode you started it with, the resultCode it returned, and any additional data from it. The resultCode will beRESULT_CANCELED if the activity explicitly returned that, didn't return any result, or crashed during its operation.

You will receive this call immediately before onResume() when your activity is re-starting.

当Activity创建时调用. 继承自Activity，一般用来初始化。

This is where most initialization should go: calling setContentView(int) to inflate the activity's UI, using findViewById(int) to programmatically interact with widgets in the UI, calling managedQuery(android.net.Uri, String[], String, String[], String) to retrieve cursors for data being displayed, etc.

You can call finish() from within this function, in which case onDestroy() will be immediately called without any of the rest of the activity lifecycle (onStart(), onResume(), onPause(), etc) executing.

Derived classes must call through to the super class's implementation of this method. If they do not, an exception will be thrown.

Perform any final cleanup before an activity is destroyed. This can happen either because the activity is finishing (someone called 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 isFinishing() method.

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 eitheronPause() or onSaveInstanceState(Bundle), not here. 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.

Derived classes must call through to the super class's implementation of this method. If they do not, an exception will be thrown.

This method will be called when an item in the list is selected. Subclasses should override. Subclasses can call getListView().getItemAtPosition(position) if they need to access the data associated with the selected item.

This is called for activities that set launchMode to "singleTop" in their package, or if a client used the FLAG_ACTIVITY_SINGLE_TOP flag when calling startActivity(Intent). In either case, when the activity is re-launched while at the top of the activity stack instead of a new instance of the activity being started, onNewIntent() will be called on the existing instance with the Intent that was used to re-launch it.

An activity will always be paused before receiving a new intent, so you can count on onResume() being called after this method.

Note that getIntent() still returns the original Intent. You can use setIntent(Intent) to update it to this new Intent.

Ensures the list view has been created before Activity restores all of the view states.

Called to retrieve per-instance state from an activity before being killed so that the state can be restored in onCreate(Bundle) or onRestoreInstanceState(Bundle) (the Bundlepopulated by this method will be passed to both).

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 onCreate(Bundle) or onRestoreInstanceState(Bundle).

Do not confuse this method with activity lifecycle callbacks such as onPause(), which is always called when an activity is being placed in the background or on its way to destruction, oronStop() which is called before destruction. One example of when onPause() and 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 onSaveInstanceState(Bundle) on B because that particular instance will never be restored, so the system avoids calling it. An example when onPause() is called and not onSaveInstanceState(Bundle) is when activity B is launched in front of activity A: the system may avoid calling onSaveInstanceState(Bundle) 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.

The default implementation takes care of most of the UI per-instance state for you by calling 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 onRestoreInstanceState(Bundle)). 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.

If called, this method will occur before onStop(). There are no guarantees about whether it will occur before or after onPause().

Called when you are no longer visible to the user. You will next receive either onRestart(), onDestroy(), or nothing, depending on later user activity.

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 onPause() method is called.

Derived classes must call through to the super class's implementation of this method. If they do not, an exception will be thrown.