Android Studio 내부 저장소 데이터로드 중 오류

Question

방금 ​​Android Studio를 배우기 시작했으며 잠시 동안 기본 메모를 작성했습니다. 메인 프래그먼트에로드/저장 메소드를 추가했습니다. 하지만 앱을 처음 시작하면 충돌이 발생합니다. 로드 메소드를 제거하고 앱을 시작하면 원하는대로 앱이 작동합니다. 로드 메소드를 다시 추가하고 두 번째로 앱을 시작한 후에도 앱이 문제없이 작동합니다. 그래서 내가 처음 시작할 때 애플 리케이션 크래시를 일으키는 내 로딩 코드에 문제가 있다고 가정합니다. 첫 번째 화면 인 주요 조각 코드와 아래 Android Studio에서받은 오류를 찾을 수 있습니다. 이 문제를 해결하도록 도와 주시면 크게 감사하겠습니다.

MainProjectList.java 조각 :

public class MainProjectLister extends ListFragment implements 
     AdapterView.OnItemClickListener, 
     AdapterView.OnItemLongClickListener { 

    Button addProjectButton; 
    EditText addProjectEditText; 
    public String projectTitle; 
    Projekt newProjekt; 
    ProjektSingleton projektSingleton; 
    ArrayList<Projekt> projektArrayList; 
    ArrayAdapter<String> adapter; 
    ArrayList<Projekt> tempProjektArrayList; 

    ArrayList<String> ListOfP; 

    private final String FILENAME="testfile15.txt"; 
    private final String FILENAME2="testfile16.txt"; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     ListOfP = new ArrayList<String>(); 
     projektSingleton = ProjektSingleton.getInstance(); 
     projektSingleton.setProjektList(getSavedArrayList()); 
     ListOfP = getSavedStringList(); 

     ((AppCompatActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(false); 
     setHasOptionsMenu(true); 

    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ 

     View view = inflater.inflate(R.layout.main_project_lister_layout, container, false); 

     addProjectButton = (Button) view.findViewById(R.id.addProjectButton); 
     addProjectEditText = (EditText) view.findViewById(R.id.addProjectEditText); 

//addProjectButton onClck method 

     addProjectButton.setOnClickListener(new View.OnClickListener(){ 
      @Override 
      public void onClick(View view){ 

//Checking if nothing is entered in the EditText and gives Error messaga 
       if(TextUtils.isEmpty(addProjectEditText.getText().toString().trim())){ 
        Toast.makeText(getActivity(), "Please type details", Toast.LENGTH_SHORT).show(); 
        return; 
       } 

       projectTitle = addProjectEditText.getText().toString(); 
       newProjekt = new Projekt(projectTitle); 
       projektArrayList = projektSingleton.getProjectList(); 
       projektArrayList.add(newProjekt); 

       ListOfP.add(projectTitle); 
       adapter.notifyDataSetChanged(); 
       saveArrayList(projektArrayList); 
       saveStringList(ListOfP); 
       addProjectEditText.setText(""); 

      } 

     }); 

     getActivity().setTitle("DearBear Notes App"); 
     return view; 

    } 

    @Override 
    public void onActivityCreated(Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 

     adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, ListOfP); 
     setListAdapter(adapter); 

     getListView().setOnItemClickListener(this); 
     getListView().setOnItemLongClickListener(this); 
    } 

    @Override 
    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l){ 

     MainProjectLister frag = new MainProjectLister(); 
     ProjectListFragmentChanger fragInterface = (ProjectListFragmentChanger) getActivity(); 
     fragInterface.projectListChangeFragment(frag); 

     projektSingleton.setProjectNumber(i); 

    } 

    @Override 
    public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l){ 
     projektArrayList = projektSingleton.getProjectList(); 
     projektArrayList.remove(i); 
     ListOfP.remove(i); 
     adapter.notifyDataSetChanged(); 
     saveArrayList(projektArrayList); 
     saveStringList(ListOfP); 

     return true; 
    } 

    //Interface 

    public interface ProjectListFragmentChanger{ 

     public void projectListChangeFragment(Fragment fragment); 

    } 

//Save File Method 
    public void saveArrayList(ArrayList<Projekt> arrayList) { 
     try { 
      FileOutputStream fos = getActivity().openFileOutput(FILENAME, Context.MODE_PRIVATE); 
      ObjectOutputStream out = new ObjectOutputStream(fos); 
      out.writeObject(arrayList); 
      out.close(); 
      fos.close(); 

     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
    } 

    public void saveStringList(ArrayList<String> arrayList) { 
     try { 
      FileOutputStream fos = getActivity().openFileOutput(FILENAME2, Context.MODE_PRIVATE); 
      ObjectOutputStream out = new ObjectOutputStream(fos); 
      out.writeObject(arrayList); 
      out.close(); 
      fos.close(); 

     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
    } 


//Load Text File Method 

    public ArrayList<Projekt> getSavedArrayList() { 
     ArrayList<Projekt> savedArrayList = null; 

     try { 
      FileInputStream fis = getActivity().openFileInput(FILENAME); 
      ObjectInputStream ois = new ObjectInputStream(fis); 
      savedArrayList = (ArrayList<Projekt>) ois.readObject(); 
      ois.close(); 
      fis.close(); 

     } catch (IOException | ClassNotFoundException e) { 
      e.printStackTrace(); 
     } 

     return savedArrayList; 
    } 

    public ArrayList<String> getSavedStringList() { 
     ArrayList<String> savedArrayList = null; 
     try { 
      FileInputStream fis = getActivity().openFileInput(FILENAME2); 
      ObjectInputStream ois = new ObjectInputStream(fis); 
      savedArrayList = (ArrayList<String>) ois.readObject(); 
      ois.close(); 
      fis.close(); 
     } catch (IOException | ClassNotFoundException e) { 
      e.printStackTrace(); 
     } 
     return savedArrayList; 
    } 
} 

오류 : 아직 생성되지 않은 파일에 openFileInput()을 호출하기 때문에 첫 번째 오류가 발생

$ adb shell am start -n "com.example.lenovo.projectlist/com.example.lenovo.projectlist.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER 
Client not ready yet..Waiting for process to come online 
Connected to process 2394 on device Nexus_5_API_24 [emulator-5554] 
I/art: Not late-enabling -Xcheck:jni (already on) 
W/art: Unexpected CPU variant for X86 using defaults: x86 
W/System: ClassLoader referenced unknown path: /data/app/com.example.lenovo.projectlist-2/lib/x86 
I/InstantRun: Instant Run Runtime started. Android package is com.example.lenovo.projectlist, real application class is null. 
I/art: Debugger is no longer active 
I/art: Starting a blocking GC Instrumentation 
W/System: ClassLoader referenced unknown path: /data/app/com.example.lenovo.projectlist-2/lib/x86 
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable 
W/System.err: java.io.FileNotFoundException: /data/user/0/com.example.lenovo.projectlist/files/testfile15.txt (No such file or directory) 
W/System.err:  at java.io.FileInputStream.open(Native Method) 
W/System.err:  at java.io.FileInputStream.<init>(FileInputStream.java:146) 
W/System.err:  at android.app.ContextImpl.openFileInput(ContextImpl.java:485) 
W/System.err:  at android.content.ContextWrapper.openFileInput(ContextWrapper.java:186) 
W/System.err:  at com.example.lenovo.projectlist.MainProjectLister.getSavedArrayList(MainProjectLister.java:189) 
W/System.err:  at com.example.lenovo.projectlist.MainProjectLister.onCreate(MainProjectLister.java:53) 
W/System.err:  at android.app.Fragment.performCreate(Fragment.java:2335) 
W/System.err:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:949) 
W/System.err:  at android.app.BackStackRecord.setLastIn(BackStackRecord.java:857) 
W/System.err:  at android.app.BackStackRecord.calculateFragments(BackStackRecord.java:880) 
W/System.err:  at android.app.BackStackRecord.run(BackStackRecord.java:727) 
W/System.err:  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578) 
W/System.err:  at android.app.FragmentController.execPendingActions(FragmentController.java:371) 
W/System.err:  at android.app.Activity.performStart(Activity.java:6680) 
W/System.err:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609) 
W/System.err:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
W/System.err:  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
W/System.err:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
W/System.err:  at android.os.Handler.dispatchMessage(Handler.java:102) 
W/System.err:  at android.os.Looper.loop(Looper.java:154) 
W/System.err:  at android.app.ActivityThread.main(ActivityThread.java:6077) 
W/System.err:  at java.lang.reflect.Method.invoke(Native Method) 
W/System.err:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
W/System.err:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
W/System.err: java.io.FileNotFoundException: /data/user/0/com.example.lenovo.projectlist/files/testfile16.txt (No such file or directory) 
W/System.err:  at java.io.FileInputStream.open(Native Method) 
W/System.err:  at java.io.FileInputStream.<init>(FileInputStream.java:146) 
W/System.err:  at android.app.ContextImpl.openFileInput(ContextImpl.java:485) 
W/System.err:  at android.content.ContextWrapper.openFileInput(ContextWrapper.java:186) 
W/System.err:  at com.example.lenovo.projectlist.MainProjectLister.getSavedStringList(MainProjectLister.java:208) 
W/System.err:  at com.example.lenovo.projectlist.MainProjectLister.onCreate(MainProjectLister.java:54) 
W/System.err:  at android.app.Fragment.performCreate(Fragment.java:2335) 
W/System.err:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:949) 
W/System.err:  at android.app.BackStackRecord.setLastIn(BackStackRecord.java:857) 
W/System.err:  at android.app.BackStackRecord.calculateFragments(BackStackRecord.java:880) 
W/System.err:  at android.app.BackStackRecord.run(BackStackRecord.java:727) 
W/System.err:  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578) 
W/System.err:  at android.app.FragmentController.execPendingActions(FragmentController.java:371) 
W/System.err:  at android.app.Activity.performStart(Activity.java:6680) 
W/System.err:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609) 
W/System.err:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
W/System.err:  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
W/System.err:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
W/System.err:  at android.os.Handler.dispatchMessage(Handler.java:102) 
W/System.err:  at android.os.Looper.loop(Looper.java:154) 
W/System.err:  at android.app.ActivityThread.main(ActivityThread.java:6077) 
W/System.err:  at java.lang.reflect.Method.invoke(Native Method) 
W/System.err:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
W/System.err:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
D/AndroidRuntime: Shutting down VM 


        --------- beginning of crash 
E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.example.lenovo.projectlist, PID: 2394 
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lenovo.projectlist/com.example.lenovo.projectlist.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference 
         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646) 
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
         at android.app.ActivityThread.-wrap12(ActivityThread.java) 
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
         at android.os.Handler.dispatchMessage(Handler.java:102) 
         at android.os.Looper.loop(Looper.java:154) 
         at android.app.ActivityThread.main(ActivityThread.java:6077) 
         at java.lang.reflect.Method.invoke(Native Method) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
        Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference 
         at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:344) 
         at android.widget.ListView.setAdapter(ListView.java:493) 
         at android.app.ListFragment.setListAdapter(ListFragment.java:240) 
         at com.example.lenovo.projectlist.MainProjectLister.onActivityCreated(MainProjectLister.java:111) 
         at android.app.Fragment.performActivityCreated(Fragment.java:2361) 
         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1014) 
         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1171) 
         at android.app.BackStackRecord.run(BackStackRecord.java:815) 
         at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578) 
         at android.app.FragmentController.execPendingActions(FragmentController.java:371) 
         at android.app.Activity.performStart(Activity.java:6680) 
         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609) 
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)  
         at android.app.ActivityThread.-wrap12(ActivityThread.java)  
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)  
         at android.os.Handler.dispatchMessage(Handler.java:102)  
         at android.os.Looper.loop(Looper.java:154)  
         at android.app.ActivityThread.main(ActivityThread.java:6077)  
         at java.lang.reflect.Method.invoke(Native Method)  
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)  
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)  
Application terminated. 

Answer 1

. 하지만 그 오류를 잡았으므로 getSavedArrayList()은 null을 반환하고 그 값을 ListOfP에 할당하면 null을 ArrayAdapter에 할당하려고 할 때 NullPointerException이 발생합니다.

이를 방지하려면 파일이 먼저 있는지 확인하고 빈 파일에 목록을 할당하여 두 가지 오류가 발생하지 않도록해야합니다. 좋아요 :

public ArrayList<Projekt> getSavedArrayList() { 
    ArrayList<Projekt> savedArrayList = null; 
    try { 
     // get the file and check if it exists before trying to read it 
     File savedFile = new File(getActivity().getFilesDir(), FILENAME); 
     if (savedFile.exists()) { 
      // if the file containing the list exists, read it and return the list 
      FileInputStream fis = getActivity().openFileInput(FILENAME); 
      ObjectInputStream ois = new ObjectInputStream(fis); 
      savedArrayList = (ArrayList<Projekt>) ois.readObject(); 
      ois.close(); 
      fis.close(); 
     } else { 
      // if it doesn't exist, return an empty list 
      savedArrayList = new ArrayList<>(); 
     } 
    } catch (IOException | ClassNotFoundException e) { 
     e.printStackTrace(); 
    } 
    return savedArrayList; 
}