Fragment Viewpager Adapter

http://wangxinghe.me/blog/2015-02-02/android-FragmentPagerAdapter-FragmentStatePagerAdapter/

First, Fragmentpageradapter

Suitable for Fragment a very limited number of cases. When a page is not visible, the view for that page may be destroyed, but all fragment will remain in memory.

If the fragment need to save a lot of state, it will lead to large memory consumption, so for a large number of fragment, we recommend the use of Fragmentstatepageradapter.
When you use Fragmentpageradapter, ViewPager you must have a valid ID.

@Overridepublic Object Instantiateitem (viewgroup container, int position) {if (mcurtransaction = = null) {Mcurt    Ransaction = Mfragmentmanager.begintransaction ();    } final Long itemId = Getitemid (position);    Do we already has this fragment?    String name = Makefragmentname (Container.getid (), itemId);    Fragment Fragment = Mfragmentmanager.findfragmentbytag (name);        if (fragment! = null) {if (DEBUG) log.v (TAG, "Attaching Item #" + ItemId + ": f=" + fragment);    Mcurtransaction.attach (fragment);        } else {fragment = GetItem (position);        if (DEBUG) log.v (TAG, "Adding Item #" + ItemId + ": f=" + fragment);    Mcurtransaction.add (Container.getid (), Fragment, Makefragmentname (Container.getid (), itemId));        } if (Fragment! = Mcurrentprimaryitem) {fragment.setmenuvisibility (false);    Fragment.setuservisiblehint (FALSE); } return fragment;} @Overridepublic void Destroyitem (ViewGroup container, int position, Object object) {if (mcurtransaction = = null) {mcurtransaction = Mfragmentmanager.begintransaction (); } if (DEBUG) log.v (TAG, "Detaching Item #" + getitemid (position) + ": f=" + object + "v=" + ((Fragment) obje    CT). GetView ()); Mcurtransaction.detach ((Fragment) object);} private static String makefragmentname (int viewId, long id) {return "Android:switcher:" + viewId + ":" + ID;}

　　

Through the source code, you can see Fragmentpageradapter fill each page of the process:
(1) According to Containerid and position get fragment tag
(2) Fragmentmanager according to the tag to find the corresponding fragment, if there is a direct attach
(3) If it does not exist, call GetItem (position) and set tag to call the Add method.

Conclusion:
(1) The tag of fragment in Fragmentpageradapter is "Android:switcher:" + viewId + ":" + ID;
(2) GetItem (position) in new Fragment (), and do not need to set tag,fragment.instantiate () to

Second, Fragmentstatepageradapter

Suitable for a large number of fragment cases. When the page is not visible, the corresponding fragment instance may be destroyed, but the fragment state will be saved.

As a result, each fragment consumes less memory, but page switching can cause significant overhead.
When using Fragmentstatepageradapter, Viewpager must have a valid ID.

@Overridepublic Object Instantiateitem (viewgroup container, int position) {//If We already has this item instantiate  D, there is nothing//to do.    This can happen when we is restoring the entire pager//from its saved state, where the fragment manager has already    Taken care of restoring the fragments we previously had instantiated.        if (mfragments.size () > position) {Fragment F = mfragments.get (position);        if (f! = null) {return F;    }} if (mcurtransaction = = null) {mcurtransaction = Mfragmentmanager.begintransaction ();    } Fragment Fragment = GetItem (position);    if (DEBUG) log.v (TAG, "Adding Item #" + Position + ": f=" + fragment);        if (msavedstate.size () > position) {fragment.savedstate FSS = msavedstate.get (position);        if (FSS! = null) {fragment.setinitialsavedstate (FSS);    }} while (Mfragments.size () <= position) {mfragments.add (null); } fragment.Setmenuvisibility (FALSE);    Fragment.setuservisiblehint (FALSE);    Mfragments.set (position, fragment);    Mcurtransaction.add (Container.getid (), fragment); return fragment;} @Overridepublic void Destroyitem (ViewGroup container, int position, object object) {Fragment Fragment = (Fragment) obje    Ct    if (mcurtransaction = = null) {mcurtransaction = Mfragmentmanager.begintransaction (); } if (DEBUG) log.v (TAG, "Removing Item #" + Position + ": f=" + object + "v=" + ((Fragment) object). GetView (    ));    while (Msavedstate.size () <= position) {msavedstate.add (null);    } msavedstate.set (position, mfragmentmanager.savefragmentinstancestate (fragment));    Mfragments.set (position, NULL); Mcurtransaction.remove (fragment);}

　　

According to the source code, Fragmentstatepageradapter fills the flow of each page:
(1) First try to find mfragments list in the index for position whether there is fragment, if there is a direct return;
(2) If not, call GetItem (position) to instantiate the fragment and set the initial state, call the Add
Destruction Process:
(1) Save the Fragment corresponding state (2) Remove Fragment

Conclusion:
(1) Fragment tag with no specified format
(2) Fragmentstatepageradapter will maintain and restore the status of fragment

Fragment Viewpager Adapter