android - 如何正确显示动态 jsonObjects

Question

我有这个 json:

{
  "title": "Sample title of this json",
  "excerpt": "Sample excerpt for the json. Random alphabets: yehodjjd uushdkjnjk jghdd",
  "tags": {
    "chlorine": {
      "name": "chlorine",
      "post_count": 32,
    },
    "flourine": {
      "name": "flourine",
      "post_count": 78,
    }
  },
}

“标题”、“摘录” 和“标签” 是已知键。它们始终是“标题”、“摘录” 和“标签”。另一方面，“标签” 中的 JsonObjects 是动态的。让我解释一下。

这个json中对象的个数是2个，但也有可能是1个，2个甚至7个。这里只有“氯”和“氟”，但物体可能只是任何东西。所以换句话说，我事先不知道“标签”中的对象。

我想做的是在 TextView 中显示“title”和“except”，到目前为止它是有效的。

我还想在一种动态列表中显示“标签”中的动态对象，我选择了 RecyclerView，这似乎不起作用。对象被解析得很好，但问题是显示它。

这些是我的代码:

fragment_details.xml

<android.support.v4.widget.NestedScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:scrollbars="vertical"
    android:fillViewport="true"
    android:id="@+id/details_layout"
    tools:context=".Fragment.DetailsFragment">

    <RelativeLayout

        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/details_relat">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:id="@+id/dpost_title"
            android:visibility="gone"
            android:layout_margin="5dp"
            android:textStyle="bold"/>

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/dpost_title"
            android:textColorLink="@color/textlink"
            android:visibility="invisible"
            android:id="@+id/dpost_content"
            android:layout_margin="5dp"/>

        <android.support.v7.widget.RecyclerView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/tag_cat_recy"/>

    </RelativeLayout>

</android.support.v4.widget.NestedScrollView>

tags_cats_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:id="@+id/tag_cat_lin"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tag_cat_text"/>

</LinearLayout>

TagCatItem

public class TagCatItem {
    private String tagCatName;
    private int tagCatCount;

    public String getTagCatName() {
        return tagCatName;
    }

    public void setTagCatName(String tagCatName) {
        this.tagCatName = tagCatName;
    }


    public int getTagCatCount() {
        return tagCatCount;
    }

    public void setTagCatCount(int tagCatCount) {
        this.tagCatCount = tagCatCount;
    }
}

细节 fragment

public class DetailsFragment extends Fragment{

    private List<TagCatItem> mTagCatItem;
    RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    LinearLayoutManager mLayoutManager;

    TextView postTitle, postContent;

    public DetailsFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        Log.d(TAG, "onCreateView called");
        // Inflate the layout for this fragment
        view =  inflater.inflate(R.layout.fragment_details, container, false);

        postTitle = (TextView)view.findViewById(R.id.dpost_title);
        postContent = (TextView) view.findViewById(R.id.dpost_content);

        mRecyclerView = (RecyclerView) view.findViewById(R.id.tag_cat_recy);

        getPost();

        return view;
    }


    private void  getPost() {
        Log.d(TAG, "getPost called"); 

        JsonObjectRequest postDetails = new JsonObjectRequest(Method.GET, url, null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        Log.d(TAG, "onResponse for getPOst called");
                        parseJson(response);
                    }
                },
                new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.d(TAG,  "onErrorResponse for getPost called");
            }
        });

        //Creating requestqueue
        RequestQueue requestQueue = Volley.newRequestQueue(getActivity());

        //Adding request queue
        requestQueue.add(postDetails);
    }
    private void parseJson(JSONObject object) {
        Log.d(TAG, "Parsing Json");
        try {
            mTitle = String.valueOf(Html.fromHtml(object.getString("title")));
            postTitle.setText(mTitle);

            mLayoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
            mRecyclerView.setLayoutManager(mLayoutManager);
            mAdapter = new TagCatAdapter(mTagCatItem, getActivity());
            mRecyclerView.setAdapter(mAdapter);

            String content = object.getString("content");
            postContent.setText(content);

            JSONObject tags = object.getJSONObject("tags");
            Iterator tagsObjs = tags.keys();

            while (tagsObjs.hasNext()) {
                // loop to get dynamic tag objects
                String tagObj = (String) tagsObjs.next();
                Log.d(TAG, "tagObj is " + tagObj);

                JSONObject tagObjDetails = tags.getJSONObject(tagObj);
                TagCatItem tagCatItem = new TagCatItem();
                String tagName = tagObjDetails.getString("name");
                tagCatItem.setTagCatName(tagName);
                Log.d(TAG, "Tag Name is " + tagName);

                int tagDetailsNum = tagObjDetails.getInt("post_count");
                tagCatItem.setTagCatCount(tagDetailsNum);
                Log.d(TAG, "Number of posts " + tagDetailsNum);
                mTagCatItem.add(tagCatItem);
                mAdapter.notifyItemRangeChanged(0, mAdapter.getItemCount());
            }

                //Unhiding views
                postTitle.setVisibility(View.VISIBLE);
                postContent.setVisibility(View.VISIBLE);
            }

        } catch (JSONException w) {
            w.printStackTrace();

        }
    }
    }

**TagCatAdapter**

public class TagCatAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

private Context mContext;
private List<TagCatItem> mTagCatItems;

public TagCatAdapter(List<TagCatItem> tagCatItems, Context context) {
    super();
    this.mTagCatItems = tagCatItems;
    this.mContext = context;
}


@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.tags_cats_item, parent, false);
    return new TextViewHolder(v);
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    TagCatItem tagCatItem = mTagCatItems.get(position);
    ((TextViewHolder) holder).tagCatName.setText(tagCatItem.getTagCatName());
}


public class TextViewHolder extends RecyclerView.ViewHolder{
    public TextView tagCatName;

    public TextViewHolder(View mView) {
        super(mView);
        tagCatName = (TextView) view.findViewById(R.id.tag_cat_text);
    }
}


@Override
public int getItemCount() {
    return mTagCatItems.size();
}

堆栈跟踪

07-01 20:06:25.563 21725-21725/com.ozuf.poster E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.ozuf.poster, PID: 21725
                                                                     java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference
                                                                         at com.ozuf.poster.Fragment.DetailsFragment.parseJson(DetailsFragment.java:492)
                                                                         at com.ozuf.poster.Fragment.DetailsFragment.access$600(DetailsFragment.java:73)
                                                                         at com.ozuf.poster.Fragment.DetailsFragment$7.onResponse(DetailsFragment.java:395)
                                                                         at com.ozuf.poster.Fragment.DetailsFragment$7.onResponse(DetailsFragment.java:391)
                                                                         at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:65)
                                                                         at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
                                                                         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:5910)
                                                                         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:1405)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)

从堆栈跟踪来看，第 492 行是 mTagCatItem.add(tagCatItem);

第 73 行是 public class DetailsFragment extends Fragment {

第 395 行是 parseJson(response);

第 391 行是 new Response.Listener<JSONObject>() {

尝试的解决方案

我试过移动:

mLayoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
            mRecyclerView.setLayoutManager(mLayoutManager);
            mAdapter = new TagCatAdapter(mTagCatItem, getActivity());
            mRecyclerView.setAdapter(mAdapter);

到onCreateView DetailsFragment 但它因我试图在空对象引用上调用 mTagCatItems.size() 的错误而崩溃。

Answer 1

您没有初始化 mTagCatItems，这就是它为 null 的原因(因此是 NPE)。要解决此问题，您需要更改声明 mTagCatItems 的行以同时对其进行初始化:

private List<TagCatItem> mTagCatItem = new ArrayList<TagCatItem>();