android – 通过选项卡单击检测片段何时可​​见

概述我试图检测片段在滑动视图上何时可见,以便在其可见时更新其内容.我是这样做的. public class MyFragment extends Fragment { @Override public void setUserVisibleHint(boolean isVisibleToUser) { super.setUserVisibleHint(isVisibleToUser); 我试图检测片段在滑动视图上何时可见,以便在其可见时更新其内容.我是这样做的.

public class MyFragment extends Fragment {  @OverrIDe  public voID setUserVisibleHint(boolean isVisibletoUser) {    super.setUserVisibleHint(isVisibletoUser);    if (isVisibletoUser) { }    else {  }  }}

问题是,当我进入页面时,通过它可以很好地工作,但当我在选项卡中选择页面时,它会崩溃“尝试调用虚拟方法”.

请帮帮我,谢谢

我有一个主要活动,然后是每个片段的活动.

主要：

public class Principal extends ActionBaractivity implements Actionbar.TabListener {SectionsPagerAdapter mSectionsPagerAdapter;/** * The {@link VIEwPager} that will host the section contents. */VIEwPager mVIEwPager;@OverrIDeprotected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentVIEw(R.layout.activity_principal);    // Set up the action bar.    final Actionbar actionbar = getSupportActionbar();    actionbar.setNavigationMode(Actionbar.NAVIGATION_MODE_TABS);    // Create the adapter that will return a fragment for each of the three    // primary sections of the activity.    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));    }}@OverrIDepublic boolean onCreateOptionsMenu(Menu menu) {    // Inflate the menu; this adds items to the action bar if it is present.    getMenuInflater().inflate(R.menu.menu_principal,menu);    return true;}@OverrIDepublic boolean onoptionsItemSelected(MenuItem item) {    // Handle action bar item clicks here. The action bar will    // automatically handle clicks on the Home/Up button,so long    // as you specify a parent activity in AndroIDManifest.xml.    int ID = item.getItemID();    //noinspection SimplifiableIfStatement    if (ID == R.ID.action_settings) {        return true;    }    return super.onoptionsItemSelected(item);}@OverrIDepublic voID onTabSelected(Actionbar.Tab tab,FragmentTransaction fragmentTransaction) {        mVIEwPager.setCurrentItem(tab.getposition());}@OverrIDepublic voID onTabUnselected(Actionbar.Tab tab,FragmentTransaction fragmentTransaction) {}@OverrIDepublic 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) {        Fragment fragment = new Fragment();        switch (position) {            case 0:                return fragment = new Config();            case 1:                return fragment = new SaIDas();            case 2:                return fragment = new EnTradas();            case 3:                return fragment = new Enviar();            case 4:                return fragment = new Historico();            case 5:                return fragment = new Status();            default:                break;        }        return fragment;    }    @OverrIDe    public int getCount() {        // Show 3 total pages.        return 6;    }    @OverrIDe    public CharSequence getPageTitle(int position) {        Locale l = Locale.getDefault();        switch (position) {            case 0:                return getString(R.string.Title_config).toupperCase(l);            case 1:                return getString(R.string.Title_saIDas).toupperCase(l);            case 2:                return getString(R.string.Title_enTradas).toupperCase(l);            case 3:                return getString(R.string.Title_enviar).toupperCase(l);            case 4:                return getString(R.string.Title_historico).toupperCase(l);            case 5:                return getString(R.string.Title_status).toupperCase(l);        }        return null;    }}/** * A placeholder fragment containing a simple vIEw. */public static class PlaceholderFragment extends Fragment {    /**     * The fragment argument representing the section number for this     * fragment.     */    private static final String ARG_SECTION_NUMBER = "section_number";    /**     * Returns a new instance of this fragment for the given section     * number.     */    public static PlaceholderFragment newInstance(int sectionNumber) {        PlaceholderFragment fragment = new PlaceholderFragment();        Bundle args = new Bundle();        args.putInt(ARG_SECTION_NUMBER,sectionNumber);        fragment.setArguments(args);        return fragment;    }    public PlaceholderFragment() {    }    @OverrIDe    public VIEw onCreateVIEw(LayoutInflater inflater,VIEwGroup container,Bundle savedInstanceState) {        VIEw rootVIEw = inflater.inflate(R.layout.fragment_principal,container,false);        return rootVIEw;    }}}

然后片段是：

public class EnTradas extends androID.support.v4.app.Fragment {    @OverrIDe    public voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);    }    @OverrIDe    public VIEw onCreateVIEw(LayoutInflater inflater,Bundle savedInstanceState) {        return inflater.inflate(R.layout.fragment_enTradas,false);    }    @OverrIDe    public voID setMenuVisibility(final boolean visible) {        super.setMenuVisibility(visible);        if (visible) {             run code here....    }}

解决方法 您可以通过以下两种方式执行此 *** 作：

从片段中你可以调用isVisible();

Return true if the fragment is currently visible to the user. This
means it: (1) has been added,(2) has its vIEw attached to the window,
and (3) is not hIDden.

从父活动中,您可以执行以下 *** 作：

public boolean checkIsFragVisible() {        Fragment yourFragment = getSupportFragmentManager().findFragmentByID(FRAG_HolDER_ID);        return yourFragment != null && yourFragment.isVisible();    }

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