Android:活动意外销毁,null savedInstanceState

Question

在发布此内容之前,我不打算列出我读过的每个引用,但是我已经在stackoverflow和所有关于活动/片段生命周期和维护状态的android开发人员文档中广泛阅读了类似的问题,并且没有找到解决方案.

这是我的场景:

我有一个使用FragmentPagerAdapter的主要活动(ImpulseActivity).每个片段显示我从服务器检索的单独数据列表.在ImpulseActivity的操作栏中按action_item时,您可以过滤从服务器发送的数据.为此,ImpulseActivity启动一个单独的活动(FilterEventsActivity).FilterEventsActivity将ImpulseActivity列为父活动.按下FilterEventsActivity上的后退按钮时,将使用null(Bundle savedInstanceState)重新创建ImpulseActivity(OnCreate调用).出于测试目的,我重写了OnSaveInstanceState并将假数据放在outState中.请注意,这种情况适用于从ImpulseActivity启动的每个活动.

我的问题是:

在这种特定情况下,防止每个片段需要重新加载数据的正确设计范例是什么？我宁愿不使用Singleton模式,因为我的片段在其他活动中被重用.

相关的源代码,如果需要:

public class ImpulseActivity extends FragmentActivity implements
    ActionBar.TabListener {

private MapSearchFragment mSearchFragment;
private BulletinFragment mBulletinFragment;

SectionsPagerAdapter mSectionsPagerAdapter;
ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.impulse_activity);

    Log.v("ImpulseActivity", "onCreate " + savedInstanceState);

    final ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    CategoryManager manager = CategoryManager.getManager();
    manager.setListener(this);
    manager.loadCategories();

    mSectionsPagerAdapter = new SectionsPagerAdapter(
            getSupportFragmentManager());

    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);
    mViewPager
            .setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                @Override
                public void onPageSelected(int position) {
                    actionBar.setSelectedNavigationItem(position);
                }
            });

    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
        actionBar.addTab(actionBar.newTab()
                .setText(mSectionsPagerAdapter.getPageTitle(i))
                .setTabListener(this));
    }
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putDouble("Hello", 1.02);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.impulse_activity_actions, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.action_create) {
        return true;
    }
    if (id == R.id.action_filter) {
        Intent intent = new Intent(this, FilterEventsActivity.class);
        startActivity(intent);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    int position = tab.getPosition();
    mViewPager.setCurrentItem(position, true);
}

@Override
public void onEventListClick(Event e) {
    Intent mIntent = new Intent(this, EventActivity.class);
    Bundle mBundle = new Bundle();
    mBundle.putSerializable(EventDetailsFragment.Event_Key, e);
    mIntent.putExtras(mBundle);
    startActivity(mIntent);
}

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {

        Fragment fragment;
        switch(position) {
            case 0:
                if (mBulletinFragment != null) {
                    fragment = mBulletinFragment;
                } else {
                    fragment = new BulletinFragment();
                    mBulletinFragment = (BulletinFragment) fragment;
                }
                break;
            case 1:
                fragment = new MapSearchFragment();
                mSearchFragment = (MapSearchFragment) fragment;
                break;
            case 2:
                fragment = new MyEventsFragment();
                break;
            default:
                fragment = new BulletinFragment();
                break;
        }
        Bundle args = new Bundle();
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
            case 0:
                return "Bulletin";
            case 1:
                return "Map";
            case 2:
                return "My Events";
            default:
                return "Test";
        }
    }
}
}

AndroidManifest.xml中

<activity
        android:name=".Home.ImpulseActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".Event.EventActivity"
        android:label="@string/title_activity_event"
        android:parentActivityName=".Home.ImpulseActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value=".Home.ImpulseActivity" />
    </activity>

Answer 1

虽然问题提到碎片,但问题实际上是导航.

向上导航的默认实现与标准激活的预期不完全相同.特别是,当父活动具有launchMode="standard"(默认值)时,按下向上按钮将创建它的新实例,而不是返回到前一个实例.

有两种方法可以解决这个问题:

1. 改变launchMode的ImpulseActivity,以singleTop在清单.

2. 覆盖主页按钮操作以使用FLAG_ACTIVITY_CLEAR_TOP标志启动意图.例如,在EventActivity.onOptionsItemSelected():

   if (id == android.R.id.home)
   {
       Intent intent = NavUtils.getParentActivityIntent(this);
       intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
       NavUtils.navigateUpTo(this, intent);
       return true;
   }
   

这些中的任何一个都会将您的旧活动带到堆栈顶部.