アンドロイドメーカー：Androidのランタイム致命的な例外ここで

Question

がLOGです：すべての私の構文はまったくエラーがないように見えるので、

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) 

私は本当にこの問題を解決するための助けを必要と私は助けてください医学リマインダのアプリをやって、私は 'AddMedicine'ボタンを押すたびにアプリがクラッシュした。以下は、問題のインタフェースのコーディングです：

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

button_saveのidを持つButton要素があなたのR.layout.activity_add_medicine xmlファイルに欠けているように見えます。

findViewById()は、idまたはnullの要素を返します。そのようなIDを持つ要素が見つからなかったためです。