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[英]NullPointerException on a CardView implementation into a RecycleView
[英]Fragment with RecycleView + CardView (FATAL EXCEPTION)
我是編程新手,我很難設置這個 RECYCLEVIEW。 請幫我。 如果可以的話,主要問題出在片段中。 我相信。
ERROR Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager) ' on a null object reference at com.example.application. Fragments.Home.HomeFragment.onCreate(HomeFragment.java:32)
由@Shay kin修復
ERROR Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference at com.example.application. Fragments.Home.HomeFragment.onCreateView(HomeFragment.java:36)
由@Shay kin修復
主要活動
class MainActivity extends AppCompatActivity {
private BottomNavigationView bottomNavigationView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bottomNavigationView = findViewById(R.id.bottonNavigationView);
loadFragment(new HomeFragment());
setBottomNavigationView();
}
private void loadFragment(Fragment fragment) {
// create a FragmentManager
FragmentManager fragmentManager = getSupportFragmentManager();
// create a FragmentTransaction to begin the transaction and replace the Fragment
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
// replace the FrameLayout with new Fragment
fragmentTransaction.replace(R.id.idMainFrameLayout, fragment);
fragmentTransaction.commit(); // save the changes
//crédits abhiandroid
}
@SuppressLint("NonConstantResourceId")
public void setBottomNavigationView() {
bottomNavigationView.setOnNavigationItemSelectedListener(item -> {
switch (item.getItemId()) {
case R.id.btnSearch:
loadFragment(new SearchFragment());
break;
case R.id.btnFeed:
loadFragment(new FeedFragment());
break;
case R.id.btnShedule:
loadFragment(new SheduleFragment());
break;
case R.id.btnProfile:
loadFragment(new ProfileFragment());
break;
default:
loadFragment(new HomeFragment());
}
return true;
});
}
}
分段
class HomeFragment extends Fragment {
private RecyclerView recyclerView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_home, container, false);
recyclerView = container.findViewById(R.id.recycleViewHome);
recyclerView.setAdapter(new MyAdapter(getMyList()));
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
return view;
}
private ArrayList<Store> getMyList() {
String mTitle = "Google", mSubTitle = "Description";
int imageView = R.drawable.ic_google_svg;
ArrayList<Store> storeArrayList = new ArrayList<>();
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
storeArrayList.add(new Store(imageView, mTitle, mSubTitle));
return storeArrayList;
}
}
RecycleView(ADAPTERVIEW + VIEWHOLDER)
class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyHolder> {
private ArrayList<Store> storeArrayList;
public MyAdapter(ArrayList<Store> storeArrayList) {
this.storeArrayList = storeArrayList;
}
@NonNull
@Override
public MyHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_layout_stores, null, false);
return new MyHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyHolder myholder, int position) {
myholder.mImageView.setImageResource(storeArrayList.get(position).getPhotoId());
myholder.mTitle.setText(storeArrayList.get(position).getmTitle());
myholder.mSubTitle.setText(storeArrayList.get(position).getSubTitle());
}
@Override
public int getItemCount() {
return storeArrayList.size();
}
public class MyHolder extends RecyclerView.ViewHolder {
private ImageView mImageView;
private TextView mTitle, mSubTitle;
public MyHolder(@NonNull View itemView) {
super(itemView);
this.mImageView = itemView.findViewById(R.id.btnImageStore);
this.mTitle = itemView.findViewById(R.id.txtTitleStore);
this.mSubTitle = itemView.findViewById(R.id.txtsubTitle);
}
}
}
用戶界面片段
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
tools:context=".Fragments.Home.HomeFragment">
<androidx.recyclerview.widget.RecyclerView
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
android:id="@+id/recycleViewHome"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginStart="20dp"
android:layout_marginTop="10dp"
android:layout_marginEnd="20dp"
android:orientation="vertical"
tools:listitem="@layout/card_layout_stores" />
</LinearLayout>
項目清單
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/cardViewShop"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:backgroundTint="#F4511E"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="110dp"
android:layout_marginStart="5dp"
android:layout_marginTop="5dp"
android:layout_marginEnd="5dp"
android:layout_marginBottom="5dp"
android:orientation="horizontal"
android:padding="10dp">
<ImageView
android:id="@+id/btnImageStore"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:scaleType="centerInside"
tools:srcCompat="@tools:sample/avatars" />
<LinearLayout
android:layout_width="250dp"
android:layout_height="match_parent"
android:layout_marginStart="10dp"
android:gravity="center_vertical"
android:orientation="vertical">
<TextView
android:id="@+id/txtTitleStore"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/NameStore"
android:textSize="14sp"
android:textStyle="bold" />
<TextView
android:id="@+id/txtsubTitle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/DescriptionStore" />
</LinearLayout>
</LinearLayout>
</androidx.cardview.widget.CardView>
你得到這個錯誤是因為在onCreate()
方法之前調用了onCreateView()
方法,所以你嘗試在初始化RecyclerView之前設置Adapter和LayoutManager ,所以你需要在OnCreateView()
方法中添加Adapter和LayoutManager 。 請在此處查看片段生命周期: https://developer.android.com/guide/fragments/lifecycle#states
而且您還創建了兩個RecyclerView實例,一個在Fragment上,另一個在onCreateView()
中,因此您需要將所有代碼從onCreate()
移動到Fragment中的onCreateView()
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