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我的Android应用程序中有另一个问题或错误。对不起，我是Android开发新手，但这是我的激情，我会坚持下去。按钮单击更新recyclerview
无论如何，我的代码在我的CustomAdapter类的方法调用中崩溃。
这是我CustomAdapter类在那里崩溃：
public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.CustomViewHolder> {
private ArrayList<UserInfo> arrayList = new ArrayList<UserInfo>();
float ratings;
public CustomAdapter(ArrayList<UserInfo> arrayList){
this.arrayList = arrayList;
}
@Override
public CustomViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.userslayout, parent, false);
CustomViewHolder customViewHolder = new CustomViewHolder(view);
return customViewHolder;
}
@Override
public void onBindViewHolder(final RecyclerViewHolder holder, int position) {
final UserInfo userInfo = arrayList.get(position);
holder.username.setText(userInfo.getMusicName());
holder.forename.setText(userInfo.getMusicCategory());
holder.surname.setText(userInfo.getFileType());
// THE APP CRASHES WHEN I CLICK THIS BUTTON. THINGS UPDATE IN THE
// DATABASE - BUT THE RECYCLERVIEW CRASHES AND THE APP CRASHES
holder.buttonRefresh.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String pressed = Integer.toString(userInfo.getPressedName());
UserListRecycler userListRecycler = new UserListRecycler();
UserListRecycler.UserPressedAsync userPressedAsync = userListRecycler.new UserPressedAsync();
userPressedAsync.execute(username, pressed);
}
});
}
}
这是我UserListRecycler类 - 主类和内部类UserPressedAsync
public class UserListRecycler extends Fragment {
RecyclerView recyclerView;
static UserAdapter adapter;
RecyclerView.LayoutManager layoutManager;
ArrayList<UserInfo> list;
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.userlistGUI, container, false);
recyclerView = (RecyclerView) rootView.findViewById(R.id.reUsers);
recyclerView.setHasFixedSize(true);
list = new ArrayList<UserInfo>();
// Instantiate new adapter here
adapter = new MusicRecyclerAdapter(list);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(linearLayoutManager);
// Sets the adapter here
recyclerView.setAdapter(adapter);
adapter.notifyDataSetChanged();
return rootView;
}
@Override
public void onStart() {
super.onStart();
populateRecyclerList();
}
public void populateList(){
PopulateUsers userList = new PopulateUsers(list, adapter, recyclerView);
userList.execute();
}
public class UserPressedAsync extends AsyncTask<String, String, String> {
@Override
protected String doInBackground(String... params) {
// REST STUFF HAPPENS HERE
}
@Override
protected void onPostExecute(String postData) {
// CRASHES HERE!!!
populateRecyclerList();
}
}
}
这是我的PopulateUsers班 - 我的服务器的详细信息通过REST
public class PopulateUsers extends AsyncTask<String, String, String> {
static ArrayList<UserInfo> list;
UserAdapter adapter;
RecyclerView recyclerView;
public PopulateUsers(ArrayList<UserInfo> list, UserAdapter adapter, RecyclerView recyclerView) {
this.list = new ArrayList<UserInfo>();
this.adapter = new UserAdapter();
this.list = list;
this.adapter = adapter;
this.recyclerView = recyclerView;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
// `REST` Activity happens here
}
@Override
protected void onPostExecute(String s) {
try {
list.clear();
JSONArray jsonArray = new JSONArray(s);
for (int i = 0; i < jsonArray.length(); i++) {
String forename = jsonArray.getJSONObject(i).getString("forename");
String surname = jsonArray.getJSONObject(i).getString("surname");
String nationality = jsonArray.getJSONObject(i).getString("nationality");
UserInfo userInfo = new UserInfo(forename, surname, nationality);
list.add(userInfo);
}
recyclerView.setAdapter(adapter);
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}
基本上，单击该按钮时，事情正在朝着backend更新，即phpmyadminmysql服务器 - 但它崩溃的应用程序不与更新的列表刷新。这与UserListRecycler类中的populateList()方法有关，它指向PopulateUsers类中的recyclerView.setAdapter(adapter);错误 - 正好在中，错误类型为NullPointerException，但它在UserListRecycler类首次实例化并加载时工作正常。那么为什么它会崩溃，当我打电话给populateList()方法？
这是我的堆栈跟踪：
java.lang.NullPointerException
at lukasz.usersapp.PopulateUsers.onPostExecute(PopulateUsers.java:67)
at lukasz.usersapp.PopulateUsers.onPostExecute(PopulateUsers.java:27)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
这将真正意味着很多，其实有些睡眠自己，如果有人可以帮助我解决这个问题。这是一个可怕的错误！
那么我该如何解决这个可怕的错误？我实际上无法入睡，并且一直将我的头撞在墙上 –
有没有办法可以修复我的代码？当然，它正在移动一条线 –
你的json从哪里来？从api？ – hehe