我已经为存储在Firebase数据库中的项目创建了arraylist。我能够在recyclerview中列出项目。甚至搜索也可以。但是，在单击recyclerview列表中的项目时，该单击在搜索列表中有效，但在常规列表中无效。代码在下面给出
public class MainActivity extends AppCompatActivity implements Adapter.SelectedProject {
DatabaseReference mDatabase;
ArrayList<projects> list;
RecyclerView PList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
PList = findViewById(R.id.ProjList);
PList.setHasFixedSize(true);
mDatabase = FirebaseDatabase.getInstance().getReference().child("Projects");
}
@Override
protected void onStart() {
super.onStart();
if (mDatabase != null) {
mDatabase.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
list = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
list.add(ds.getValue(projects.class));
}
Adapter adapter = new Adapter(list, null);
PList.setAdapter(adapter);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Toast.makeText(MainActivity.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_home, menu);
MenuItem item = menu.findItem(R.id.search);
SearchView searchView = (SearchView) item.getActionView();
if (searchView != null) {
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
search(newText);
return true;
}
});
}
return super.onCreateOptionsMenu(menu);
}
private void search(String str) {
ArrayList<projects> sList = new ArrayList<>();
for (projects object : list) {
if (object.getPname().toLowerCase().contains(str.toLowerCase())) {
sList.add(object);
}
}
Adapter adapter = new Adapter(sList, this);
PList.setAdapter(adapter);
}
@Override
public void selectedProject(projects projects) {
startActivity(new Intent(MainActivity.this, InfoActivity.class));
}
}
适配器类
public class Adapter extends RecyclerView.Adapter < Adapter.ProjViewHolder > {
private ArrayList < projects > list;
private SelectedProject selectedProject;
public Adapter(ArrayList < projects > list, SelectedProject selectedProject) {
this.list = list;
this.selectedProject = selectedProject;
}
@NonNull
@Override
public ProjViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.proj_list, parent, false);
return new ProjViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull ProjViewHolder holder, int position) {
holder.prname.setText(list.get(position).getPname());
holder.prlocation.setText(list.get(position).getPlocation());
}
@Override
public int getItemCount() {
return list.size();
}
public interface SelectedProject {
void selectedProject(projects projects);
}
class ProjViewHolder extends RecyclerView.ViewHolder {
TextView prname, prlocation;
public ProjViewHolder(@NonNull View itemView) {
super(itemView);
prname = itemView.findViewById(R.id.FPName);
prlocation = itemView.findViewById(R.id.FPLocation);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
selectedProject.selectedProject(list.get(getAdapterPosition()));
}
});
}
}
}
该选择在搜索适配器中被接受。
Adapter adapter = new Adapter(sList,this);
但是普通适配器显示以下代码错误。
Adapter adapter = new Adapter(list,this);
但是，如果我将其更改为null，如下所示，则错误消失。
Adapter adapter = new Adapter(list,null);
但是当我单击时，该应用程序已关闭。
请让我知道如何纠正错误？
stackrace详细信息
java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.volq.Adapter$SelectedProject.selectedProject(com.example.volq.projects)' on a null object reference
at com.example.volq.Adapter$ProjViewHolder$1.onClick(Adapter.java:68)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
注意如何设置适配器以进行搜索与普通设置之间的区别
Adapter adapter = new Adapter(sList, this); // `this`as the second parameter/listener is ok
但是对于另一个：
Adapter adapter = new Adapter(list, null);
这里侦听器为空，此错误是有道理的：
java.lang.NullPointerException：尝试调用接口方法'无效com.example.volq.Adapter $ SelectedProject.selectedProject（com.example.volq.projects）'在null对象引用
上
而不是null，只需在Activity的MainActivity.this回调中传递onStart()：
Adapter adapter = new Adapter(list, MainActivity.this);
但是普通适配器显示以下代码错误。
Adapter adapter = new Adapter(list,this);
是因为this没有在MainActivity回调中引用onDataChange()，而是引用了ValueEventListener