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”是已知密钥。它们始终是“标题”，“摘录”和“标签”。另一方面，“tags”中的JsonObjects是动态的。让我解释一下。
在这个json中对象的数量是两个，但它可能是一个对象，两个甚至七个。 这里只有“氯”和“氟”，但物体可能就是任何东西。 所以换句话说，我事先并不知道“标签”中的对象。
我想要做的是在TextView中显示“title”和“except”，到目前为止一直有效。
我还想在一种动态列表中的“标签”中显示动态对象，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;
}
}
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();
}
}
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，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>() {
尝试解决方案
我尝试过移动：
mLayoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
mRecyclerView.setLayoutManager(mLayoutManager);
mAdapter = new TagCatAdapter(mTagCatItem, getActivity());
mRecyclerView.setAdapter(mAdapter);
到 DetailsFragment 的onCreateView但是它崩溃了我试图在空对象引用上调用 mTagCatItems.size（）的错误。
答案 0 :(得分：1)
您没有初始化mTagCatItems，这就是为什么它为空（因此是NPE）。要解决此问题，您需要更改声明mTagCatItems的行以初始化它：
private List<TagCatItem> mTagCatItem = new ArrayList<TagCatItem>();