Android 选项卡监听器在后台保持 2 个选项卡处于 Activity 状态

Question

我的应用程序中有一个选项卡 Activity ，

这里是一些简化的代码:

@SuppressLint("NewApi")
public class Rhino68PanelActivity extends FragmentActivity implements ActionBar.TabListener {

static String TAG = "Rhino68PanelActivty";

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
 * will keep every loaded fragment in memory. If this becomes too memory
 * intensive, it may be best to switch to a
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 */
SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_rhino68_panel);

    // Set up the action bar.
    final ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the app.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    // When swiping between different sections, select the corresponding
    // tab. We can also use ActionBar.Tab#select() to do this if we have
    // a reference to the Tab.
    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            actionBar.setSelectedNavigationItem(position);
        }
    });

    // For each of the sections in the app, add a tab to the action bar.
    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
        // Create a tab with text corresponding to the page title defined by
        // the adapter. Also specify this Activity object, which implements
        // the TabListener interface, as the callback (listener) for when
        // this tab is selected.
        actionBar.addTab(actionBar.newTab().setText(mSectionsPagerAdapter.getPageTitle(i)).setTabListener(this));
    }
}

@Override
protected void onDestroy() {
    super.onDestroy();
    Network.cancelRequests(Rhino68PanelActivity.this);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.rhino68_panel, menu);
    return true;
}   

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    // When the given tab is selected, switch to the corresponding page in
    // the ViewPager.
    mViewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        Fragment fragment = null;

        switch (position) {
        case 0: {
            fragment = new OneSectionFragment();
        }
            break;
        case 1: {
            fragment = new TwoSectionFragment();
        }
            break;
        case 2: {
            fragment = new ThreeSectionFragment();
        }
            break;
        default: {
            fragment = new OneSectionFragment();
        }
        }
        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 "1";
        case 1:
            "2";
        case 2:
            "3";
        }
        return null;
    }
}

public static class oneSectionFragment extends Fragment {


    private static Context mContext;

    public StatusSectionFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_rhino68_panel_status, container, false);
        mContext = getActivity();
        // update view
        ....
        return rootView;
    }
    //fucntions and methods
}

    public static class twoSectionFragment extends Fragment {


    private static Context mContext;

    public StatusSectionFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_rhino68_panel_status, container, false);
        mContext = getActivity();
        // update view
        ....
        return rootView;
    }
    //fucntions and methods
}

现在我注意到一些奇怪的事情，我不确定它是如何工作的还是我做错了什么。

我在每个 sectionfragments onCreateView() 中设置了一个断点，现在取决于我在选项卡之间导航的方式，断点是否命中。

案例一: 如果我从选项卡 1 开始，然后导航到选项卡 2 - 没有遇到断点 如果我然后返回选项卡 1 - 再次没有遇到断点

案例二: 如果我从选项卡 1 开始，然后导航到选项卡 2 - 没有遇到断点 如果我然后转到选项卡 3 - 选项卡 3 中的断点被击中， 如果我然后回到 2 - 没有断点 如果我然后转到 1 - tab 1 断点被击中

当您点击 2 号标签时，它似乎加载了 3 号标签。现在这是选项卡管理器的属性吗？还是我的标签管理器只认为有 2 个标签？

我应该在哪里运行必须在选项卡实际出现时更新的代码？

Answer 1

尝试使用:

mViewPager.setOffscreenPageLimit(x);

此方法设置在空闲状态下应保留在 View 层次结构中当前页面任一侧的页面数。此设置默认为 1。 http://developer.android.com/reference/android/support/v4/view/ViewPager.html#setOffscreenPageLimit(int)