Android Studio: Android Runtime Fatal Exception

Question

Hier ist der LOG:

E/AndroidRuntime: FATAL EXCEPTION: main 
         Process: com.example.chong.medicinereminder, PID: 3221 
         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.chong.medicinereminder/com.example.chong.medicinereminder.AddMedicine}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646) 
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
          at android.app.ActivityThread.-wrap12(ActivityThread.java) 
          at android.app.ActivityThread$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$MethodAndArgsCaller.run(ZygoteInit.java:865) 
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
         Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
          at com.example.chong.medicinereminder.AddMedicine.onCreate(AddMedicine.java:36) 
          at android.app.Activity.performCreate(Activity.java:6664) 
          at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) 
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599) 
          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) 

ich wirklich Hilfe benötigen, dieses Problem zu lösen, weil alle meine Syntax scheinen überhaupt keine Fehler zu haben, bitte helfen ich bin macht eine Medizinerinnerung App und die App stürzte jedes Mal, wenn ich den 'AddMedicine' Knopf drückte. Unten ist die Codierung von Problem-Schnittstelle:

public class AddMedicine extends AppCompatActivity { 
    EditText med_name, med_reason, med_dosage; 
    List<MedicineList> MedicineList = new ArrayList<MedicineList>(); 


    @Override 
    protected void onCreate(final Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_add_medicine); 

     med_name = (EditText) findViewById(R.id.text_med_name); 
     med_reason = (EditText) findViewById(R.id.text_med_reason); 
     med_dosage = (EditText) findViewById(R.id.text_med_dosage); 

     final Button button_save = (Button) findViewById(R.id.button_save); 
     button_save.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       saveMedicine(med_name.getText().toString(), med_reason.getText().toString(), med_dosage.getText().toString()); 
       Toast.makeText(getApplicationContext(), med_name.getText().toString() + " has been added to the list", Toast.LENGTH_SHORT).show(); 
      } 

     }); 

     med_name.addTextChangedListener(new TextWatcher() { 
      @Override 
      public void beforeTextChanged(CharSequence s, int start, int count, int after) { 

      } 

      @Override 
      public void onTextChanged(CharSequence s, int start, int before, int count) { 
       button_save.setEnabled(!med_name.getText().toString().trim().isEmpty()); 
      } 

      @Override 
      public void afterTextChanged(Editable s) { 

      } 
     }); 
    } 

    private void saveMedicine(String name, String reason, String dosage) { 
     MedicineList.add(new MedicineList(name, reason, dosage)); 
    } 

    private class MedicineListAdapter extends ArrayAdapter<MedicineList> { 


     public MedicineListAdapter() { 
      super(AddMedicine.this, R.layout.medicine_list, MedicineList); 
     } 

     @Override 
     public View getView(int position, View view, ViewGroup parent) { 
      if (view == null) 
       view = getLayoutInflater().inflate(R.layout.medicine_list, parent, false); 
      MedicineList currentMedicine = MedicineList.get(position); 

      TextView name = (TextView) view.findViewById(R.id.medicine_name); 
      name.setText(currentMedicine.getName()); 

      TextView reason = (TextView) view.findViewById(R.id.medicine_reason); 
      reason.setText(currentMedicine.getReason()); 

      TextView dosage = (TextView) view.findViewById(R.id.medicine_dosage); 
      dosage.setText(currentMedicine.getDosage()); 

      return view; 
     } 


    } 


    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.menu_medicine_add, menu); 
     return true; 
    } 

} 

Answer 1

es wie ein mit der ID von button_saveButton Elemente sieht in Ihrer R.layout.activity_add_medicine XML-Datei fehlt.

Da findViewById() Element für angegebene id oder null zurückgibt, wenn Element mit einer solchen ID nicht gefunden wurde.