我試圖挽救兩個片段的狀態。我希望他們在更改Android設備的語言時重新顯示(當我離開活動並返回時)。這兩個片段被聲明爲活動的屬性和兩個延伸android.support.v4.app.Fragment類。這是什麼,我將它們保存在活動中展示他們:保存碎片狀態給出錯誤:INT java.util.ArrayList.size()」上一個空對象引用
@Override
protected void onSaveInstanceState(Bundle outState) {
if(settingsFragment.isAdded())
this.getSupportFragmentManager().putFragment(outState,settingsFragment.TAG,settingsFragment);
if(historyFragment.isAdded())
this.getSupportFragmentManager().putFragment(outState,historyFragment.TAG,historyFragment);
}
這是他們是如何獲取的(記住,這是方法是所謂的onCreate()方法,只是的setContentView後()法):
private void instantiateFragments(Bundle inState) {
FragmentManager manager = getFragmentManager();
if (inState != null) { //the line 254 is just below
settingsFragment = (SettingsFragment) this.getSupportFragmentManager().getFragment(inState, SettingsFragment.TAG);
historyFragment = (HistoryFragment) this.getSupportFragmentManager().getFragment(inState, HistoryFragment.TAG);
} else {
settingsFragment = SettingsFragment.newInstance("Settings","0");
historyFragment = HistoryFragment.newInstance("History","1");
}
}
這是我當我試圖加載回活動收到錯誤:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.UI.Activities.ExampleActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2802)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2867)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4594)
at android.app.ActivityThread.access$1000(ActivityThread.java:181)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1482)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6134)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:872)
at com.example.UI.Activities.ExampleActivity.instantiateFragments(ExampleActivity.java:254)
at com.example.UI.Activities.ExampleActivity.onCreate(ExampleActivity.java:102)
at android.app.Activity.performCreate(Activity.java:6374)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2746)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2867)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4594)
at android.app.ActivityThread.access$1000(ActivityThread.java:181)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1482)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6134)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
你們可以幫我明白是怎麼回事,怎麼我可以解決嗎?這(這意味着,我怎樣才能從它的活動保存片段的實例)。謝謝
編輯 對於那些要我來顯示和隱藏,顯示settingsFragment,這是我使用的方法:
protected void displayFragmentSettings() {
FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
if (settingsFragment.isAdded()) { // if the fragment is already in container
ft.show(settingsFragment);
} else { // fragment needs to be added to frame container
ft.add(R.id.body, settingsFragment, "Settings");
}
// Hide fragment B
if (historyFragment.isAdded()) { ft.hide(historyFragment); }
// Hide fragment C
// if (fragmentC.isAdded()) { ft.hide(fragmentC); }
// Commit changes
ft.commit();
}
我做同樣的任何其他片段,我需要顯示。
我已經這樣做,當我想從一個片段切換到另一個。在這裏,我想舉個例子,按下中心最下面的按鈕來進入Android設備的主頁面,在選項中更改語言,按左鍵並選擇我的應用程序。如果它是一個活動,它將重新加載,沒有問題。我試圖用片段實現相同的結果 –
這些片段旨在保留附加到活動的片段的實例。如果我理解正確,請按主頁按鈕並轉到應用程序,然後從最近的應用程序中選擇您的應用程序。你不必做任何事情。它應該從你離開的同一點恢復。您始終可以在片段上使用setRetainInstance(true)。 – Hitesh
你能告訴我如何以及在何處使用setRetainInstance(真),到目前爲止,我沒能找到。 –