Java Android Studio:RecyclerView不显示数据

我目前正在制作一个带有提要的Android应用程序，因此我可以使用来自QuickBlox的自定义数据显示一个小博客。我希望每条记录都出现在CardView中，下面有一张图片和一个标题，然后当用户点击卡片时，它会展开以显示有关它的更多细节。然而，我的尝试总是以它没有在RecyclerView上显示卡片而告终。我确实有它下载的数据，但我不知道为什么它没有显示出来

保存主代码的片段是

HomeRecycleServicewFragment

，适配器是

CustomAdapter

，布局XML是

fragment\u home.XML

HomeRecycleServicewFragment：

public class HomeRecyclerViewFragment extends Fragment {

private static final String TAG = "HomeRecyclerViewFragment";
private static final String KEY_LAYOUT_MANAGER = "layoutManager";
private static final int SPAN_COUNT = 2;
private static final int DATASET_COUNT = 60;
private QBCustomObject qbco;
public static ProgressDialog dia;
HashMap<String, Object> fields = new HashMap<String, Object>();
public List<String> ids;
Handler myHandler;

private enum LayoutManagerType {
    GRID_LAYOUT_MANAGER,
    LINEAR_LAYOUT_MANAGER
}

protected LayoutManagerType mCurrentLayoutManagerType;

protected CardView mLinearLayoutRadioButton;
protected CardView mGridLayoutRadioButton;

protected RecyclerView mRecyclerView;
protected CustomAdapter mAdapter;
protected RecyclerView.LayoutManager mLayoutManager;
protected String[] mDataset;

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

    // Initialize dataset, this data would usually come from a local content provider or
    // remote server.
    dia = ProgressDialog.show(this.getContext(), null,"Downloading recent posts...");
    dia.show();
    initDataset();
    myHandler = new Handler();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_home, container, false);
    rootView.setTag(TAG);

    mRecyclerView = (RecyclerView) rootView.findViewById(R.id.homerecyclerview);

    // LinearLayoutManager is used here, this will layout the elements in a similar fashion
    // to the way ListView would layout elements. The RecyclerView.LayoutManager defines how
    // elements are laid out.
    mLayoutManager = new LinearLayoutManager(getActivity());

    mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;

    if (savedInstanceState != null) {
        // Restore saved layout manager type.
        mCurrentLayoutManagerType = (LayoutManagerType) savedInstanceState
                .getSerializable(KEY_LAYOUT_MANAGER);
    }
    setRecyclerViewLayoutManager(mCurrentLayoutManagerType);

    mAdapter = new CustomAdapter(mDataset);
    // Set CustomAdapter as the adapter for RecyclerView.
    //mRecyclerView.setAdapter(mAdapter);

    mLinearLayoutRadioButton = (CardView) rootView.findViewById(R.id.card_view);
    mLinearLayoutRadioButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setRecyclerViewLayoutManager(LayoutManagerType.LINEAR_LAYOUT_MANAGER);
        }
    });
    //mRecyclerView.setAdapter(mAdapter);

    updateUI();
    return rootView;
}

/**
 * @param layoutManagerType Type of layout manager to switch to.
 */
public void setRecyclerViewLayoutManager(LayoutManagerType layoutManagerType) {
    int scrollPosition = 0;

    // If a layout manager has already been set, get current scroll position.
    if (mRecyclerView.getLayoutManager() != null) {
        scrollPosition = ((LinearLayoutManager) mRecyclerView.getLayoutManager())
                .findFirstCompletelyVisibleItemPosition();
    }

    switch (layoutManagerType) {
        case GRID_LAYOUT_MANAGER:
            mLayoutManager = new GridLayoutManager(getActivity(), SPAN_COUNT);
            mCurrentLayoutManagerType = LayoutManagerType.GRID_LAYOUT_MANAGER;
            break;
        case LINEAR_LAYOUT_MANAGER:
            mLayoutManager = new LinearLayoutManager(getActivity());
            mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
            break;
        default:
            mLayoutManager = new LinearLayoutManager(getActivity());
            mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
    }

    mRecyclerView.setLayoutManager(mLayoutManager);
    mRecyclerView.scrollToPosition(scrollPosition);
}

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    // Save currently selected layout manager.
    savedInstanceState.putSerializable(KEY_LAYOUT_MANAGER, mCurrentLayoutManagerType);
    super.onSaveInstanceState(savedInstanceState);
}


private void initDataset() {

    QBCustomObjects.getObjects("posts", (QBCallback) qbco, new QBCallbackImpl() {
        @Override
        public void onComplete(Result result) {
            if (result.isSuccess()) {
                Log.i(this.toString(),"Retrieved posts successfully.");
                dia.dismiss();
                QBCustomObjectLimitedResult coresult = (QBCustomObjectLimitedResult) result;
                ArrayList<QBCustomObject> co = coresult.getCustomObjects();


                int sum = 0;

                for (int i = 0; i < co.size(); ++i) {
                    ids.add(co.get(i).getCustomObjectId());
                    sum += Arrays.toString(co.toArray()).toCharArray()[i];
                }
                String[] stockArr = new String[ids.size()];

                stockArr = ids.toArray(stockArr);
                mDataset = stockArr;

                updateUI();
            } else {
                dia.dismiss();
                Log.e("Errors",result.getErrors().toString());
            }
        }
    });
    dia.dismiss();
}

private void updateUI() {
    mAdapter = new CustomAdapter(mDataset);
    mRecyclerView.setAdapter(mAdapter);
}
}

---

如果我理解您的要求，您的cardView应该位于另一个布局xml中，而不是与recycleview位于同一个xml中，然后在您的onCreateViewHolder中传递该项以创建视图，

---

为了了解R RecyclerView

Ok，我已将CardView移动到另一个XML中，但它刚刚崩溃（在编辑1中发布日志以减少注释混乱）

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {
private String[] mDataset;
private Uri[] imgUriList;
private List<String> listOfTitles;
private QBCustomObject qbco;
public ProgressDialog dia;
HashMap<String, Object> fields = new HashMap<String, Object>();
public List<String> ids;


private String id;
private String name;
private String description;
private String year;
private float rating;
private long date;

Handler myHandler;

// Provide a reference to the views for each data item
// Complex data items may need more than one view per item, and
// you provide access to all the views for a data item in a view holder
public static class MyViewHolder extends RecyclerView.ViewHolder {
    public CardView mCardView;
    public TextView mTextView;
    public MyViewHolder(View v) {
        super(v);

        mCardView = (CardView) v.findViewById(R.id.card_view);
        mTextView = (TextView) v.findViewById(R.id.info_text);

    }
}

// Provide a suitable constructor (depends on the kind of dataset)
public CustomAdapter(String[] myDataset) {
    mDataset = myDataset;

}

// Create new views (invoked by the layout manager)
@Override
public CustomAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
                                                 int viewType) {
    // create a new view
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.fragment_home, parent, false);
    // set the view's size, margins, paddings and layout parameters
    MyViewHolder vh = new MyViewHolder(v);
    dia = ProgressDialog.show(v.getContext(), null,"Downloading recent posts...");
    dia.show();
    myHandler = new Handler();
    //initQb();

    return vh;

}

@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
    holder.mTextView.setText(mDataset[position]);
}

@Override
public int getItemCount() {

    if (mDataset != null) return mDataset.length;
    else return 0;
}

public void initQb() {
    QBCustomObjects.getObjects("posts", (QBCallback) qbco, new QBCallbackImpl() {
        @Override
        public void onComplete(Result result) {
            if (result.isSuccess()) {
                QBCustomObjectLimitedResult coresult = (QBCustomObjectLimitedResult) result;
                ArrayList<QBCustomObject> co = coresult.getCustomObjects();
                dia.dismiss();
                Log.println(Log.INFO,"PostGetHandler","Retrieved posts successfully.");
                int sum = 0;

                for (int i = 0; i < co.size(); ++i) {
                    ids.add(co.get(i).getCustomObjectId().toString());
                    sum += co.toArray().toString().toCharArray()[i];
                }
                String[] stockArr = new String[ids.size()];
                stockArr = ids.toArray(stockArr);
                CustomAdapter ca = new CustomAdapter(stockArr);

            } else {
                dia.dismiss();
                Log.e("Errors",result.getErrors().toString());
            }
        }
    });
}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="1"
android:id="@+id/linearlayoutv"
xmlns:tools="http://schemas.android.com/tools"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:background="@drawable/splashscreen">



<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/homerecyclerview">    </android.support.v7.widget.RecyclerView>
<android.support.v7.widget.CardView
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    card_view:cardCornerRadius="4dp"
    android:layout_weight="0.25"
    android:layout_height="match_parent"
    android:layout_marginLeft="5dp"
    android:layout_marginRight="5dp"
    android:layout_marginTop="5dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="212dp"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/info_text"
            android:layout_width="347dp"
            android:layout_height="34dp"
            android:textSize="16sp"
            android:foregroundGravity="bottom"
            android:gravity="bottom"
            android:layout_marginTop="180dp" />

        <ImageView
            android:id="@+id/myImage"
            android:layout_width="wrap_content"
            android:layout_gravity="fill_horizontal"
            android:layout_height="wrap_content" />


    </LinearLayout>
</android.support.v7.widget.CardView>
</LinearLayout>

FATAL EXCEPTION: main
                                                                                Process: com.example.adamangle.ameroboticsapp, PID: 2977
                                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.CardView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                    at io.github.adamangle.ameroboticsapp.fragments.HomeRecyclerViewFragment.onCreateView(HomeRecyclerViewFragment.java:105)
                                                                                    at android.support.v4.app.Fragment.performCreateView(Fragment.java:2074)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1286)
                                                                                    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:758)
                                                                                    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1671)
                                                                                    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:532)
                                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                    at android.os.Looper.loop(Looper.java:135)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:5221)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)