java - 无法交换 ViewPager 中显示的 fragment

Question

我正在更改一个应用程序的导航，使其工作方式如下:该应用程序将包含一个 Activity ，该 Activity 最初显示一个具有三个 View ( fragment )的 ViewPager，并且在其中一个 View 中有一个按钮可以用另外两个 fragment 替换这些 fragment 。

我在 this answer 中发现我不能使用 FragmentPagerAdapter 因为它在第一次显示后永远不会销毁 fragment ；因为我希望交换 fragment ，所以我将不得不使用 FragmentStatePagerAdapter，同时确保始终在方法 getItem(int position) 中返回一个新的 fragment 实例。但是，为了让 ViewPager 在更改绑定(bind)到它的适配器后有效地更新 View (实际上我不更改适配器，只更改与其关联的数据，我用它来实例化 fragment )，我必须覆盖方法 getItemPosition(Object object) 以使其返回 POSITION_NONE 并在适配器中调用 notifyDataSetChanged()。但是，在该过程之后 View 没有更新(这正是我的问题)。

我的代码如下:

ConfiguracoesDeItemDoViewPager.java(包含适配器实例化新 fragment 所需的数据):

public static class ConfiguracoesDeItemDoViewPager {

    private String nomeDaAba;
    private Class<? extends FragmentoBase> classeDoFragmento;
    private Bundle argumentosDoFragmento;

    public ConfiguracoesDeItemDoViewPager(String nomeDaAba, Class<? extends FragmentoBase> classeDoFragmento, Bundle argumentosDoFragmento) {
        this.nomeDaAba = nomeDaAba;
        this.classeDoFragmento = classeDoFragmento;
        this.argumentosDoFragmento = argumentosDoFragmento;
    }

    public String getNomeDaAba() {
        return nomeDaAba;
    }

    public void setNomeDaAba(String nomeDaAba) {
        this.nomeDaAba = nomeDaAba;
    }

    public Class<? extends FragmentoBase> getClasseDoFragmento() {
        return classeDoFragmento;
    }

    public void setClasseDoFragmento(
            Class<? extends FragmentoBase> classeDoFragmento) {
        this.classeDoFragmento = classeDoFragmento;
    }

    public Bundle getArgumentosDoFragmento() {
        return argumentosDoFragmento;
    }

    public void setArgumentosDoFragmento(Bundle argumentosDoFragmento) {
        this.argumentosDoFragmento = argumentosDoFragmento;
    }
}

Constantes.java(提供数据以使用一组 fragment 配置 ViewPager):

public class Constantes {

    public static final ConfiguracoesDeItemDoViewPager [] CONFIGURACOES_DO_VIEWPAGER_1;
    public static final ConfiguracoesDeItemDoViewPager [] CONFIGURACOES_DO_VIEWPAGER_2;

    // Bloco de inicialização de valores estáticos 
    static {
        CONFIGURACOES_DO_VIEWPAGER_1 = new DadosDeItemDoViewPager[3];
        CONFIGURACOES_DO_VIEWPAGER_1[0] = new DadosDeItemDoViewPager("Aba 1", FragmentoA.class, null);
        CONFIGURACOES_DO_VIEWPAGER_1[1] = new DadosDeItemDoViewPager("Aba 2", FragmentoB.class, null);
        CONFIGURACOES_DO_VIEWPAGER_1[2] = new DadosDeItemDoViewPager("Aba 3", FragmentoC.class, null);

        CONFIGURACOES_DO_VIEWPAGER_2 = new DadosDeItemDoViewPager[2];
        CONFIGURACOES_DO_VIEWPAGER_2[0] = new DadosDeItemDoViewPager("Aba 1", FragmentoD.class, null);
        CONFIGURACOES_DO_VIEWPAGER_2[1] = new DadosDeItemDoViewPager("Aba 2", FragmentoE.class, null);
    }

...

}

AtividadePrincipal.java(应用程序中唯一的 Activity ，具有 FragmentStatePagerAdapter 的内部类):

public class AtividadePrincipal extends ActionBarActivity {

    private ViewPager mViewPager;
    private TabsPagerAdapter mTabsPagerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mTabsPagerAdapter = new TabsPagerAdapter(getSupportFragmentManager(), Constantes.CONFIGURACOES_DO_VIEWPAGER_1);
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mTabsPagerAdapter);
    }

    public void exibirViewPager2() {
        ((TabsPagerAdapter)mViewPager.getAdapter()).setConfiguracoesParaInicializarViewPager(Constantes.CONFIGURACOES_DO_VIEWPAGER_2);
    }

    public class TabsPagerAdapter extends FragmentStatePagerAdapter {

        private FragmentManager mFragmentManager; 
        private ConfiguracoesDeItemDoViewPager [] mConfiguracoesDeItensDoViewPager;

        public TabsPagerAdapter(FragmentManager fm, ConfiguracoesDeItensDoViewPager [] configuracoesDeItensDoViewPager) {
            super(fm);
            this.mFragmentManager = fm;
            this.mConfiguracoesDeItensDoViewPager = configuracoesDeItensDoViewPager;
        }

        @Override
        public int getItemPosition(Object object) {
            return POSITION_NONE;
        }

        @Override
        public Fragment getItem(int indice) {

            Fragment fragmento = null;

            try {
                fragmento = mConfiguracoesDeItensDoViewPager[indice].getClasseDoFragmento().newInstance();
                if (mConfiguracoesDeItensDoViewPager[indice].getArgumentosDoFragmento() != null) {
                    fragmento.setArguments(mConfiguracoesDeItensDoViewPager[indice].getArgumentosDoFragmento());
                }
            } catch (IllegalAccessException e) {
                Log.e(Logs.gerarTagParaFiltragemNoLogCat(AtividadePrincipal.this, this), "Exceção inesperada!", e); 
            } catch (InstantiationException e) {
                Log.e(Logs.gerarTagParaFiltragemNoLogCat(AtividadePrincipal.this, this), "Exceção inesperada!", e); 
            }
            return fragmento;
        }    

        @Override
        public int getCount() {
            return mConfiguracoesDeItensDoViewPager.length;
        }

        @Override
        public CharSequence getPageTitle(int posicao) {
           return mConfiguracoesDeItensDoViewPager[posicao].getNomeDaAba();
        }

        public void setConfiguracoesParaInicializarViewPager(ConfiguracoesDeItemDoViewPager [] configuracoes) {
            // Remove um fragmento extra contido dentro do FragmentoB, que se for
            // deixado no FragmentManager causa erro de id duplicado
            FragmentTransaction ft = mFragmentManager.beginTransaction();
            Fragment fragmento = mFragmentManager.findFragmentById(R.id.mapa);
            if (fragmento != null && fragmento instanceof SupportMapFragment) {
                ft.remove(fragmento);
            }
            ft.commit();

            this.mConfiguracoesDeItensDoViewPager = configuracoes;

            notifyDataSetChanged();
        }
    }
}

只是为了完成解释:当用户单击其中一个 fragment 中的按钮时，方法 AtividadePrincipal.exibirViewPager2() 被调用。它应该更新 ViewPager View /fragment ，但这并没有发生。

Answer 1

我已经试过了，它会重新创建/重新加载 fragment (调用 onCreate)。在您的 AtividadePrincipal.exibirViewPager2() 方法中添加这一行。

    this.mViewPager.setAdapter(mTabsPagerAdapter);