我试图挽救两个片段的状态。我希望他们在更改Android设备的语言时重新显示(当我离开活动并返回时)。这两个片段被声明为活动的属性和两个延伸android.support.v4.app.Fragment类。这是什么,我将它们保存在活动中展示他们:保存碎片状态给出错误:INT java.util.ArrayList.size()”上一个空对象引用
@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);
}
这是他们是如何获取的(记住,这是方法是所谓的onCreate()方法,只是的setContentView后()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");
}
}
这是我当我试图加载回活动收到错误:
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)
你们可以帮我明白是怎么回事,怎么我可以解决吗?这(这意味着,我怎样才能从它的活动保存片段的实例)。谢谢
编辑 对于那些要我来显示和隐藏,显示settingsFragment,这是我使用的方法:
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();
}
我做同样的任何其他片段,我需要显示。
我已经这样做,当我想从一个片段切换到另一个。在这里,我想举个例子,按下中心最下面的按钮来进入Android设备的主页面,在选项中更改语言,按左键并选择我的应用程序。如果它是一个活动,它将重新加载,没有问题。我试图用片段实现相同的结果 –
这些片段旨在保留附加到活动的片段的实例。如果我理解正确,请按主页按钮并转到应用程序,然后从最近的应用程序中选择您的应用程序。你不必做任何事情。它应该从你离开的同一点恢复。您始终可以在片段上使用setRetainInstance(true)。 – Hitesh
你能告诉我如何以及在何处使用setRetainInstance(真),到目前为止,我没能找到。 –