java - 在创建时将对象传递给滑动选项卡 fragment

Question

我试图将在创建方法的主要 Activity 期间检索和创建的对象传递给滑动选项卡布局的 fragment 之一。

由于该对象是通过网络连接创建的，我的计划是在创建主 Activity 期间接收数据，然后将结果对象传递给我的 fragment 。然而，这似乎说起来容易做起来难。然后，生成的对象将传递到 Forecast fragment 中的回收器 View 。

我已经阅读了各种方法，包括在我的模型对象上实现 Parcelable 接口(interface)，将其存储为 bundle 并尝试将其发送到 fragment 。然而它总是空的。我相信这是因为我在内存中创建了一个新 fragment ，并且没有将包传递给显示的 fragment 。我也没有任何 fragment 的 ID，因此不可能通过 ID 定位它们，至少据我所知。

如果有人能指出我正确的方向，我将不胜感激。

主 Activity.java

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MAIN ACTIVITY";
@Bind(R.id.toolBar) Toolbar mToolbar;
@Bind(R.id.viewPager) ViewPager mViewPager;
@Bind(R.id.tabLayout) SlidingTabLayout mTabLayout;

private ViewPagerAdapter mAdapter;
private String mForecastsTabName = "Forecasts";
private String mAlertsTabName = "Alerts";
private String mTabTitles[] = {mForecastsTabName, mAlertsTabName};
private  int mNumberOfTabs = 2;
private Forecast[] mForecasts;
private JsonParser mJsonParser = new JsonParser();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.bind(this);
    setSupportActionBar(mToolbar);

    setupSlidingTabs();
}

private void setupSlidingTabs() {
    // Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
    mAdapter = new ViewPagerAdapter(getSupportFragmentManager(), mTabTitles, mNumberOfTabs);

    // Assigning the ViewPages View and setting the adapter
    mViewPager.setAdapter(mAdapter);

    // Assigning the Sliding Tab Layout View
    mTabLayout.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width
    // Setting Custom Color for the Scroll bar indicator of the Tab View
    mTabLayout.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
        @Override
        public int getIndicatorColor(int position) {
            return getResources().getColor(R.color.ColorAccent);
        }
    });

    mTabLayout.setViewPager(mViewPager);
}

预测Fragment.java

public class ForecastFragment extends Fragment {

private static final String FORECAST_KEY = "FORECAST_KEY";
private static final String TAG = "FRAGMENT";
private Forecast[] mForecasts;

@Bind(R.id.recyclerView) RecyclerView mRecyclerView;
@Bind(R.id.emptyView) TextView mEmptyView;
@Bind(R.id.locationButton) Button mLocationButton;

public static ForecastFragment newInstance(Forecast[] forecasts) {
    ForecastFragment fragment = new ForecastFragment();
    Bundle bundle = new Bundle();
    bundle.putParcelableArray(FORECAST_KEY, forecasts);
    fragment.setArguments(bundle);
    return fragment;
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Initialize dataset, this data would usually come from a local content provider or
    // remote server.
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.forecast_tab_fragment, container, false);
    ButterKnife.bind(this, view);

    displayEmptyViewIfNoData();

    ForecastAdapter adapter = new ForecastAdapter(getActivity(), mForecasts);
    mRecyclerView.setAdapter(adapter);

    RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
    mRecyclerView.setLayoutManager(layoutManager);

    return view;
}


private void displayEmptyViewIfNoData() {
    if (mForecasts == null || mForecasts.length < 1) {
        mRecyclerView.setVisibility(View.GONE);
        mEmptyView.setVisibility(View.VISIBLE);
        mLocationButton.setVisibility(View.VISIBLE);
    }
    else {
        mRecyclerView.setVisibility(View.VISIBLE);
        mEmptyView.setVisibility(View.GONE);
        mLocationButton.setVisibility(View.GONE);
    }
}

@OnClick(R.id.locationButton)
public void selectLocations(View view) {
    Intent intent = new Intent(getActivity(), LocationSelectionActivity.class);
    intent.putExtra(ActivityConstants.CALLING_ACTIVITY, ActivityConstants.FORECAST_ACTIVITY);
    startActivity(intent);
}

}

ViewPagerAdapter.java

public class ViewPagerAdapter extends FragmentStatePagerAdapter {
// This will Store the Titles of the Tabs which are Going to be passed when ViewPagerAdapter is created
String mTitles[];
// Store the number of tabs, this will also be passed when the ViewPagerAdapter is created
int mNumberOfTabs;
SparseArray<Fragment> registeredFragments = new SparseArray<>();

public ViewPagerAdapter(FragmentManager fm, String titles[], int numberOfTabs) {
    super(fm);
    mTitles = titles;
    mNumberOfTabs = numberOfTabs;
}

//This method return the fragment for the every position in the View Pager
@Override
public Fragment getItem(int position) {
    if (position == 0) {
        ForecastFragment forecastFragment = new ForecastFragment();
        return forecastFragment;
    }
    else if (position == 1) {
        AlertFragment alertFragment = new AlertFragment();
        return alertFragment;
    }
    return null;
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}

public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

// This method return the titles for the Tabs in the Tab Strip
@Override
public CharSequence getPageTitle(int position) {
    return mTitles[position];
}

@Override
public int getCount() {
    return mNumberOfTabs;
}

}

Forecast_tab_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@color/ColorPrimaryLight">

   <android.support.v7.widget.RecyclerView
       android:id="@+id/recyclerView"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:padding="@dimen/activity_vertical_margin"/>

   <TextView
       android:id="@+id/emptyView"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:text="@string/empty_forecast_message"
       android:textColor="@color/ColorTextPrimary"
       android:gravity="center"
       android:visibility="gone"
       android:layout_alignParentTop="true"
       android:layout_alignParentLeft="true"
       android:layout_alignParentStart="true"
       android:layout_marginTop="115dp"/>

<Button
    android:id="@+id/locationButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/button_shape"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:textColor="@color/ColorTextPrimary"
    android:text="@string/add_forecast_button"
    android:visibility="gone"
    android:layout_alignParentBottom="false"
    android:layout_centerHorizontal="true"
    android:layout_below="@+id/emptyView"
    android:layout_marginTop="24dp"/>

</RelativeLayout>

Answer 1

当您执行下面的代码时，您可以将数据传递给您的 fragment 。

在您的 Activity 中，当数据准备就绪时，调用以下方法:

mAdapter.getFragment(index).setData(dataObject);

或

mAdapter.getFragment(mViewPager.getCurrentItem()).setData(dataObject);

你的 FragmentPagerAdater 应该是这样的:

class CustomPagerAdapter extends FragmentPagerAdapter {
        SparseArray<App4StoreBaseSubFragment> registeredFragments = new SparseArray<App4StoreBaseSubFragment>();
        public CustomPagerAdapter(FragmentManager fm) {
            super(fm);
        }

@Override
    public Object instantiateItem(ViewGroup container, int position) {
        App4StoreBaseSubFragment fragment = (App4StoreBaseSubFragment) super.instantiateItem(container, position);
        registeredFragments.put(position, fragment);
        return fragment;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        registeredFragments.remove(position);
        super.destroyItem(container, position, object);
    }

        public ForecastFragment getFragment(int position){
            return registeredFragments.get(position);
        }

    }

你的 fragment 应该是这样的:

public class ForecastFragment extends Fragment {
         public void setData(Forecast forecast){
              //write code here to change UI
         }
    }