如何正確地顯示動態一個JSONObjects

Question

我有這樣的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, 
    } 
    }, 
} 

「稱號」，「摘錄」和「標籤」已知的密鑰。他們總是「標題」,「摘錄」和「標籤」。另一方面，在「標籤」 JsonObjects是動態的。讓我解釋。

這個json中對象的數量是兩個，但它可能是一個對象，兩個甚至七個對象。 只是有「氯」和「」 flourine」在這裏，但對象可能只是什麼。 因此，換句話說，我不事先知道在‘標籤’的對象。

我想要做什麼在TextView中顯示「標題」和「除外」，到目前爲止工作。

我也想在一個動態列表中顯示「標籤」中的動態對象，我選擇了RecyclerView，這似乎不是對象正在被解析，但問題是顯示它。

這些是我的代碼：

個

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; 
    } 
} 

DetailsFragment

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(); 
} 

}

堆棧跟蹤

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) 

從棧跟蹤，492行是mTagCatItem.add(tagCatItem);

線73是public class DetailsFragment extends Fragment {

395行是parseJson(response);

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

嘗試的解決方案

我已經試過移動：中

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

到onCreateView DetailsFragment，但它與我想在一個空對象引用調用mTagCatItems.size（）錯誤墜毀。

Answer 1

你沒有初始化mTagCatItems這就是爲什麼它是空的（因此是NPE）。要解決這個問題，您需要更改聲明mTagCatItems的行，以便將其初始化：

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