我制作了一张卡片视图，可以从互联网上加载数据并进行显示。我有一个JSONParser类来解析json数据。然后，我将数据存储在ListItem类型的arraylist中。但是，我无法使用onCliclListener。
这是JSONParser.java文件：
public class JSONParser extends AsyncTask<Void,Void,Boolean>{
Context c;
String jsonData;
RecyclerView rv;
private final Context context=null;
ProgressDialog pd;
ArrayList<String> names=new ArrayList<>();
ArrayList<String> ages=new ArrayList<>();
ArrayList<String> addresses=new ArrayList<>();
ArrayList<String> bgs=new ArrayList<>();
List<ListItem> data = new ArrayList<>();
public JSONParser(Context c, String jsonData, RecyclerView rv) {
this.c = c;
this.jsonData = jsonData;
this.rv = rv;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
pd=new ProgressDialog(c);
pd.setTitle("Parse JSON");
pd.setMessage("Parsing...Please wait");
pd.show();
}
@Override
protected Boolean doInBackground(Void... voids) {
return parse();
}
@Override
protected void onPostExecute(Boolean isParsed) {
super.onPostExecute(isParsed);
pd.dismiss();
if(isParsed)
{
//BIND
MyAdapter adapter=new MyAdapter(c,names,ages,addresses,bgs);
rv.setAdapter(adapter);
}else
{
Toast.makeText(c, "Unable To Parse,Check Your Log output", Toast.LENGTH_SHORT).show();
}
}
private Boolean parse()
{
try
{
JSONArray ja=new JSONArray(jsonData);
JSONObject jo;
names.clear();
ages.clear();
addresses.clear();
bgs.clear();
for (int i=0;i<ja.length();i++)
{
jo=ja.getJSONObject(i);
List<ListItem> ldata = new ArrayList<>();
ListItem item = new ListItem();
String name=jo.getString("name");
String age=jo.getString("mob");
String address=jo.getString("add");
String bg=jo.getString("bg");
names.add(name);
ages.add(age);
addresses.add(address);
bgs.add(bg);
item.setName(name);
item.setAge(age);
item.setAddress(address);
item.setBg(bg);
ldata.add(item);
setData(ldata);
}
return true;
} catch (JSONException e) {
e.printStackTrace();
return false;
}
}
public void setData(List<ListItem> data) {
this.data = data;
}
public List<ListItem> getData() {
return data;
}
}
这是MainActivity.java文件：
public class MainActivity extends AppCompatActivity implements MyAdapter.ItemClickCallback {
String jsonURL="http://projectred.in/phploginwebservice/index.php?tag=reqjson&cur=JAIPUR";
RecyclerView rv;
ArrayList listData;
JSONParser jsonParser;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
listData = (ArrayList) jsonParser.getData();
rv = (RecyclerView) findViewById(R.id.rv);
rv.setLayoutManager(new LinearLayoutManager(this));
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
new JSONDownloader(MainActivity.this,jsonURL, rv).execute();
}
});
}
@Override
public void onItemClick(int p) {
ListItem item = (ListItem) listData.get(p);
Toast.makeText(MainActivity.this, "Title: " + item.getName() + "\nSubtitle :" + item.getAge()+ "\nAddress :" + item.getAddress(), Toast.LENGTH_LONG).show();
}
@Override
public void onSecondaryIconClick(int p) {
}
}
这是我的适配器java代码：
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
Context c;
ArrayList<String> names;
ArrayList<String> ages;
ArrayList<String> addresses;
ArrayList<String> bgs;
private ItemClickCallback itemClickCallback;
public MyAdapter(Context c, ArrayList<String> names, ArrayList<String> ages, ArrayList<String> addresses, ArrayList<String> bgs) {
this.c = c;
this.names = names;
this.ages = ages;
this.addresses = addresses;
this.bgs = bgs;
}
@Override
public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(c).inflate(R.layout.model, parent, false);
return new MyViewHolder(v);
}
public interface ItemClickCallback {
void onItemClick(int p);
void onSecondaryIconClick(int p);
}
public void setItemClickCallback(final ItemClickCallback itemClickCallback) {
this.itemClickCallback = itemClickCallback;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
//BIND
holder.nameTxt.setText(names.get(position));
holder.ageTxt.setText(ages.get(position));
holder.addTxt.setText(addresses.get(position));
if (bgs.get(position).toString().equals("AP")) {
holder.bg.setImageResource(R.drawable.apr);
}
if (bgs.get(position).toString().equals("AN")) {
holder.bg.setImageResource(R.drawable.anr);
}
if (bgs.get(position).toString().equals("BP")) {
holder.bg.setImageResource(R.drawable.bpr);
}
if (bgs.get(position).toString().equals("BN")) {
holder.bg.setImageResource(R.drawable.bnr);
}
if (bgs.get(position).toString().equals("ABP")) {
holder.bg.setImageResource(R.drawable.abpr);
}
if (bgs.get(position).toString().equals("ABN")) {
holder.bg.setImageResource(R.drawable.abnr);
}
if (bgs.get(position).toString().equals("OP")) {
holder.bg.setImageResource(R.drawable.opr);
}
if (bgs.get(position).toString().equals("ON")) {
holder.bg.setImageResource(R.drawable.onr);
}
}
@Override
public int getItemCount() {
return names.size();
}
class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
TextView nameTxt, ageTxt, addTxt;
ImageView bg;
public MyViewHolder(View itemView) {
super(itemView);
nameTxt = (TextView) itemView.findViewById(R.id.textView101);
ageTxt = (TextView) itemView.findViewById(R.id.textView887);
addTxt = (TextView) itemView.findViewById(R.id.textView77);
bg = (ImageView) itemView.findViewById(R.id.imageView83);
}
@Override
public void onClick(View view) {
if (view.getId() == R.id.cont_item_root) {
itemClickCallback.onItemClick(getAdapterPosition());
} else {
itemClickCallback.onSecondaryIconClick(getAdapterPosition());
}
}
}
}
显示空指针异常。
这是我的LogCat：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List com.tutorials.hp.jsonrecyclerview.m_JSON.JSONParser.getData()' on a null object reference
at com.tutorials.hp.jsonrecyclerview.MainActivity$override.onCreate(MainActivity.java:32)
at com.tutorials.hp.jsonrecyclerview.MainActivity$override.access$dispatch(MainActivity.java)
at com.tutorials.hp.jsonrecyclerview.MainActivity.onCreate(MainActivity.java:0)
at android.app.Activity.performCreate(Activity.java:6259)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4098)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1360)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
答案 0 :(得分：2)
你应该初始化JsonParser
jsonParser = new JsonParser(c, jsonData, rv);
listData = (ArrayList) jsonParser.getData();
但是你无法立即调用jsonParser.getData，你需要等到asynctask结束。
public class JSONParser {
ProgressDialog pd;
ArrayList<String> names=new ArrayList<>();
ArrayList<String> ages=new ArrayList<>();
ArrayList<String> addresses=new ArrayList<>();
ArrayList<String> bgs=new ArrayList<>();
ArrayList<ListItem> data = new ArrayList<>();
public JSONParser(final Context c, final String jsonData, final RecyclerView rv, final OnFinishListener onFinishListener) {
new AsyncTask<Void, Void, Boolean>() {
@Override
protected void onPreExecute() {
super.onPreExecute();
pd=new ProgressDialog(c);
pd.setTitle("Parse JSON");
pd.setMessage("Parsing...Please wait");
pd.show();
}
@Override
protected Boolean doInBackground(Void... params) {
try {
JSONArray ja=new JSONArray(jsonData);
JSONObject jo;
names.clear();
ages.clear();
addresses.clear();
bgs.clear();
for (int i=0;i<ja.length();i++) {
jo=ja.getJSONObject(i);
ArrayList<ListItem> ldata = new ArrayList<>();
ListItem item = new ListItem();
String name=jo.getString("name");
String age=jo.getString("mob");
String address=jo.getString("add");
String bg=jo.getString("bg");
names.add(name);
ages.add(age);
addresses.add(address);
bgs.add(bg);
item.setName(name);
item.setAge(age);
item.setAddress(address);
item.setBg(bg);
ldata.add(item);
setData(ldata);
}
return true;
} catch (JSONException e) {
e.printStackTrace();
return false;
}
}
@Override
protected void onPostExecute(Boolean isParsed) {
super.onPostExecute(isParsed);
pd.dismiss();
if(isParsed) {
//BIND
MyAdapter adapter=new MyAdapter(c,names,ages,addresses,bgs);
rv.setAdapter(adapter);
onFinishListener.finished(data);
}else {
Toast.makeText(c, "Unable To Parse,Check Your Log output", Toast.LENGTH_SHORT).show();
}
}
}.execute();
}
public void setData(ArrayList<ListItem> data) {
this.data = data;
}
public ArrayList<ListItem> getData() {
return data;
}
public interface OnFinishListener{
void finished(ArrayList<ListItem> data);
}
}
在 MainActivity.java
中jsonParser = new JsonParser(c, jsonData, rv,new JSONParser.OnFinishListener() {
@Override
public void finished(ArrayList<ListItem> data) {
listData = data;
}
});
这应该有用，如果我错过了什么让我知道。
就像NoobGeek说你需要将setOnclickLiestenr设置为你的观点，如果你没有设置任何onclicklister，你将无法听取点击，例如，
//nameTxt.setOnClickListener(this);
//ageTxt.setOnClickListener(this);
//addTxt.setOnClickListener(this);
//i don't see the cont_item_root anywhere
//bg = (ImageView) itemView.findViewById(R.id.imageView83);
bg.setOnClickListener(this);
...
@Override
public void onClick(View view) {
if (view.getId() == R.id.imageView83) { //maybe this?
itemClickCallback.onItemClick(getAdapterPosition());
}
}
}