Fragment status switch and fragment status Switch

Fragment status switch and fragment status Switch

When you use Activity to manage multiple Fragment, replace is used for each Fragment switchover. As a result, xxx is not currently in the FragmentManager fails.

On the Internet, if replace is used for switching, the switched Fragment will be replaced, and the switched Fragment view will be deleted from the viewtree. As a result, the Fragment will be re-created every time during the switching process.

Each time you use add to add Fragment, show is used when the switchover is made, and the switched Fragment is hidden with hide. The Code is as follows:

1/** 2 * Fragment jump 3 * @ param fm 4 * @ param fragmentClass 5 * @ param tag 6 * @ param args 7 */8 public void turnToFragment (Class <? Extends Fragment> fromFragmentClass, Class <? Extends Fragment> toFragmentClass, Bundle args) {9 10 FragmentManager fm = getSupportFragmentManager (); 11 // The switched Fragment tag 12 String fromTag = fromFragmentClass. getSimpleName (); 13 // The switched Fragment tag 14 String toTag = toFragmentClass. getSimpleName (); 15 // find the switched Fragment16 Fragment fromFragment = fm. findFragmentByTag (fromTag); 17 Fragment toFragment = fm. findFragmentByTag (toTag); 18 // If the Fragment to be switched does not exist, Create 19 if (toFragment = null) {20 try {21 toFragment = toFragmentClass. newInstance (); 22 toFragment. setArguments (args); 23} catch (java. lang. instantiationException e) {24 e. printStackTrace (); 25} catch (IllegalAccessException e) {26 e. printStackTrace (); 27} 28} 29 // if any parameter is passed, 30 if (args! = Null &&! Args. isEmpty () {31 toFragment. getArguments (). putAll (args); 32} 33 // Fragment transaction 34 FragmentTransaction ft = fm. beginTransaction (); 35 // sets the Fragment switching effect 36 ft. setCustomAnimations (android. r. anim. fade_in, android. r. anim. fade_out, 37 android. r. anim. fade_in, android. r. anim. fade_out); 38/** 39 * If the Fragment to be switched is not added by the Fragment transaction, the switched Fragment is hidden and the Fragment40 * to be switched is added. Otherwise, the switched Fragment is hidden, and the Fragment41 */42 if (! ToFragment. isAdded () {43 ft. hide (fromFragment ). add (R. id. content_frame, toFragment, toTag); 44} else {45 ft. hide (fromFragment ). show (toFragment); 46} 47 // Add to return stack 48 // ft. addToBackStack (tag); 49 // commit the transaction in the unretained state 50 ft. commitAllowingStateLoss (); 51}

Here is a FragmentTransaction (transaction), which is the core class of Fragment switching. It has two methods: replace, add, replace Fragment, and add Fragment. The difference between the two is: replace = remove old fragment, add new fragment,

When our application (that is, the Activity that manages multiple Fragment) runs to the background (that is, the current screen is launched), The onPause () method of the Activity is triggered, while the onPause () method of the Activity is () it will call the same method of Fragment managed by it, but when I use replace, the original Fragment has been removed, so when I call the principle of Fragment's onPause () the preceding xxx is not currently in the FragmentManager exception occurs when the method is not crude. debug is used to verify that:

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