如何在嵌套片段中获取Activity？

Question

我正在尝试在ViewPager中包含的片段中调用getActivity()活动,并且此ViewPager包含在Fragment中.我需要在这些片段中调用此活动的一些方法,但getActivity总是为这些片段返回NULL.

我不知道这是否是一个好方法,但我需要视图寻呼机包含的片段根据操作栏操作更新其内容并显示消息说完或出现错误.

对此的帮助将不胜感激.

这是代码:

内部碎片:

    public class ReportSessionsFragment extends ReportPageFragment implements IUpdateView {

    private static final String TAG = ReportSessionsFragment.class.getSimpleName();

    private Sessions fSessions;

    private List<Report> reportList = null;
    private ReportsAdapter adapter = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        settings = ((BaseActivity)getActivity()).settings;
    }

    @Override
    public void onStart() {
        super.onStart();
        setCounter(db.getSessionsCount());

        if(settings.getSelectedRoom() != null){
            reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                    settings.getStatusSelectedList());
            adapter = new ReportsAdapter(getActivity(), reportList, EReport.Sessions);
            mRecyclerView.setAdapter(adapter);
        }

    }

    @Override
    public void onStop() {
        super.onStop();
    }

    @Override
    public void reload() {
        HashMap<String, Object> parameters = new HashMap<>();
        parameters.put(Fetcher.REQUEST_PARAMETERS, getEventInformation());

        showProgress(getString(R.string.txt_requesting_sessions));
        fSessions = new Sessions(getActivity(), this);
        fSessions.handleSession(parameters, false);
    }

    @Override
    public void delta() {

    }

    @Override
    public void updateProcess(String message) {

    }

    @Override
    public void onProcessEnded(RequestType type, boolean isProvisioningCompleted, String message) {
        reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                settings.getStatusSelectedList());
        adapter.notifyDataSetChanged();
        hideProgress();
    }

    @Override
    public void onError(Exception e, boolean isProvisioningCompleted) {
        hideProgress();
        showError(getString(R.string.txt_error_title),
                e.getMessage());
    }
}

包含ViewPager的片段:

    public class ReportSessionsFragment extends ReportPageFragment implements IUpdateView {

    private static final String TAG = ReportSessionsFragment.class.getSimpleName();

    private Sessions fSessions;

    private List<Report> reportList = null;
    private ReportsAdapter adapter = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        settings = ((BaseActivity)getActivity()).settings;
    }

    @Override
    public void onStart() {
        super.onStart();
        setCounter(db.getSessionsCount());

        if(settings.getSelectedRoom() != null){
            reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                    settings.getStatusSelectedList());
            adapter = new ReportsAdapter(getActivity(), reportList, EReport.Sessions);
            mRecyclerView.setAdapter(adapter);
        }

    }

    @Override
    public void onStop() {
        super.onStop();
    }

    @Override
    public void reload() {
        HashMap<String, Object> parameters = new HashMap<>();
        parameters.put(Fetcher.REQUEST_PARAMETERS, getEventInformation());

        showProgress(getString(R.string.txt_requesting_sessions));
        fSessions = new Sessions(getActivity(), this);
        fSessions.handleSession(parameters, false);
    }

    @Override
    public void delta() {

    }

    @Override
    public void updateProcess(String message) {

    }

    @Override
    public void onProcessEnded(RequestType type, boolean isProvisioningCompleted, String message) {
        reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                settings.getStatusSelectedList());
        adapter.notifyDataSetChanged();
        hideProgress();
    }

    @Override
    public void onError(Exception e, boolean isProvisioningCompleted) {
        hideProgress();
        showError(getString(R.string.txt_error_title),
                e.getMessage());
    }
}

活动:

    public class ReportsActivity extends BaseActivity implements IReports {

    private static final String TAG = ReportsActivity.class.getSimpleName();

    private ReportsFragment reportFragment;
    private HashMap<Integer, MenuItem> menuReports;

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

        reportFragment = new ReportsFragment();
        addFragment(reportFragment);
    }

    @Override
    protected void onStart() {
        super.onStart();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_reports, menu);

        menuReports = new HashMap<>();

        for(int index = 0; index < menu.size(); index++ ){
            MenuItem mi = menu.getItem(index);
            menuReports.put(mi.getItemId(), mi);
        }

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        ReportPageFragment reportPage = (ReportPageFragment)reportFragment.getCurrentReportPage();

        switch (item.getItemId()){
            case R.id.action_reload:
                reportPage.reload();
                break;
            case R.id.action_delta:
                reportPage.delta();
                break;
        }

        return true;
    }

    @Override
    public void displayOptionsByReport(int position) {
        MenuItem miReload = null;
        if(menuReports != null){
             miReload = (MenuItem) menuReports.get(R.id.action_reload);
        }

        switch (position){
            case REPORT_SESSION:
                miReload.setVisible(true);
                break;
            case REPORT_ENROLLMENT:
                miReload.setVisible(true);
                break;
            case REPORT_REGISTRANTS:
                miReload.setVisible(false);
                break;
            case REPORT_ASSOCIATIONS:
                miReload.setVisible(false);
                break;
        }
    }
}

FragmentPagerAdapter:

public class ReportsPagerAdapter extends FragmentStatePagerAdapter {

private Context ctx;

public ReportsPagerAdapter(Context ctx, FragmentManager fm) {
    super(fm);
    this.ctx = ctx;
}

@Override
public Fragment getItem(int position) {
    Fragment fragment = null;

    switch (position){
        case 0:
            fragment = Fragment.instantiate(ctx, ReportSessionsFragment.class.getName());
            break;
        case 1:
            fragment = Fragment.instantiate(ctx, ReportEnrollmentFragment.class.getName());
            break;
        case 2:
            fragment = Fragment.instantiate(ctx, ReportRegistrantsFragment.class.getName());
            break;
        case 3:
            fragment = Fragment.instantiate(ctx, ReportAssociationsFragment.class.getName());
            break;
    }

    return fragment;
}

@Override
public int getCount() {
    String[] reportListNames = ctx.getResources().getStringArray(R.array.reports);
    return reportListNames.length;
}

@Override
public CharSequence getPageTitle(int position) {
    String[] reportListNames = ctx.getResources().getStringArray(R.array.reports);
    return reportListNames[position];
}
}

Answer 1

每个片段,甚至是那些是另一个片段的onAttach()孩子的片段,都会在它们被添加到片段树时接收调用.包含片段的活动作为参数传入.最简单的解决方案可能是将活动保存为片段的成员.然后在以后需要时可用.

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    //save the activity to a member of this fragment
    mHostActivity = activity;
}

另一种方法是,对于总是在树中固定深度的片段,可以getParent()根据需要多次使用以获得最顶层的片段.例如,在作为寻呼机片段子节点的片段中:

getParentFragment().getActivity()