Android NullPointerError按钮单击

我试图通过读取csv文件来更新它的TextView内容中的一个按钮时在另一个片段中按下，但我不断收到FATAL EXCEPTION: main和java.lang.NullPointerException错误在第二个片段。这里是我的代码：Android NullPointerError按钮单击

public class AddFragment extends Fragment { 

    static EditText spent,saved,coupons; 
    Button writeExcelButton; 
    String data = ""; 
    Spinner spinner; 
    UpdateFile updateFile; 
    //int thisTab = 1; 

    public interface UpdateFile { 
     public void onButtonClick(); //NullPointerException error here 
    } 

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

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

     setSpinnerContent(view); 

     spent = (EditText) view.findViewById(R.id.text_spent1); 
     saved = (EditText) view.findViewById(R.id.text_saved1); 
     coupons = (EditText) view.findViewById(R.id.text_coupons1); 

     writeExcelButton = (Button) view.findViewById(R.id.button_addGroc); 
     writeExcelButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       updateFile(); 
       buttonClicked(); 
      } 
     }); 
     return view; 
    } 

    private void setSpinnerContent (View view) { 
     spinner = (Spinner) view.findViewById(R.id.groc_store); 
     ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getActivity(), 
      R.array.store1, android.R.layout.simple_spinner_item); 
     adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
     spinner.setAdapter(adapter); 
    } 

    public void updateFile() { 
     try { 
      // This is the string that should be written to file 
      String mySpin = spinner.getSelectedItem().toString(); 
      String mySpent = spent.getText().toString(); 
      String mySaved = saved.getText().toString(); 
      String myCoup = coupons.getText().toString(); 
      // This is the file that should be written to 
      File myFile = new File(Environment.getExternalStorageDirectory(), "dir/savings.csv"); 
      if (!myFile.exists()) { 
       myFile.mkdirs(); 
       myFile.createNewFile(); 
      } 
      //write to file 


      } 

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

    public void buttonClicked() { 
     updateFile.onButtonClick(); //NullPointerException error here 
    } 
}

的logcat：

11-25 20:17:10.504: E/AndroidRuntime(10733): FATAL EXCEPTION: main 
11-25 20:17:10.504: E/AndroidRuntime(10733): java.lang.NullPointerException 
11-25 20:17:10.504: E/AndroidRuntime(10733): at com.example.myfirstapp.AddFragment.buttonClicked(AddFragment.java:108) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at com.example.myfirstapp.AddFragment$1.onClick(AddFragment.java:54) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.view.View.performClick(View.java:4240) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.view.View$PerformClick.run(View.java:17721) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.os.Handler.handleCallback(Handler.java:730) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.os.Handler.dispatchMessage(Handler.java:92) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.os.Looper.loop(Looper.java:137) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at android.app.ActivityThread.main(ActivityThread.java:5103) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at java.lang.reflect.Method.invokeNative(Native Method) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at java.lang.reflect.Method.invoke(Method.java:525) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
11-25 20:17:10.504: E/AndroidRuntime(10733): at dalvik.system.NativeStart.main(Native Method)

任何帮助将不胜感激。

编辑

我将此添加到我上面的代码：

@Override 
public void onAttach(Activity activity) { 
    super.onAttach(activity); 
     try { 
      updateFile = (UpdateFile) activity; 
     } catch (ClassCastException e) { 
      throw new ClassCastException(activity.toString() 
        + " must implement UpdateFile"); 
     } 
}

但现在我与其他错误我相处收到此错误：

11-25 20:43:27.957: E/AndroidRuntime(25938): at com.example.myfirstapp.MainActivity.onButtonClick(MainActivity.java:66)

这里的方法我在我的MainActivity：

public void onButtonClick() { 
     HistoryFragment historyFragment = (HistoryFragment) getSupportFragmentManager().findFragmentById(R.id.tableLayout1); 
     historyFragment.updateTable(); 
    }

这是我试图更新片段：

public class HistoryFragment extends Fragment { 

    static TextView pos1, pos2, pos3, pos4, pos5, pos6, pos7, pos8, pos9, pos10, pos11, pos12; 

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

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

     pos1 = (TextView)view.findViewById(R.id.grocstore1); 
     pos2 = (TextView)view.findViewById(R.id.grocspent1); 
     pos3 = (TextView)view.findViewById(R.id.grocsaved1); 
     pos4 = (TextView)view.findViewById(R.id.groccoupons1); 
     pos5 = (TextView)view.findViewById(R.id.grocstore2); 
     pos6 = (TextView)view.findViewById(R.id.grocspent2); 
     pos7 = (TextView)view.findViewById(R.id.grocsaved2); 
     pos8 = (TextView)view.findViewById(R.id.groccoupons2); 
     pos9 = (TextView)view.findViewById(R.id.grocstore3); 
     pos10 = (TextView)view.findViewById(R.id.grocspent3); 
     pos11 = (TextView)view.findViewById(R.id.grocsaved3); 
     pos12 = (TextView)view.findViewById(R.id.groccoupons3); 

     return view; 
    } 

    public void updateTable() { 
     File myFile = new File(Environment.getExternalStorageDirectory(), "dir/savings.csv"); 
     String line; 
     ArrayList<String> savingList = new ArrayList<String>(); 
     try { 
      BufferedReader reader = new BufferedReader(new FileReader(myFile)); 
      while((line = reader.readLine()) != null) { 
       String[] strings = line.split(","); 
       for(String s : strings) { 
        savingList.add(1, s); 
        System.out.println(savingList.get(1)); 
       } 
       pos1.setText(strings[1]); 
       System.out.println(pos1); 
       pos2.setText(strings[2]); 
       pos3.setText(strings[3]); 
       pos4.setText(strings[4]); 
       pos5.setText(strings[5]); 
       pos6.setText(strings[6]); 
       pos7.setText(strings[7]); 
       pos8.setText(strings[8]); 
       pos9.setText(strings[9]); 
       pos10.setText(strings[10]); 
       pos11.setText(strings[11]); 
       pos12.setText(strings[12]); 
      } 
      reader.close(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 

    } 
}

对不起，我是新来的这一点，我已经在这个现在凝视了好几个小时。

来源

2013-11-26 user3033922

我有不好的感觉，你误会了接口。 – hendrix

请参阅http://docs.oracle.com/javase/tutorial/java/concepts/interface.html – hendrix

您从未将任何值分配给updateFile。它始终为空。

在你的onCreate()（或其他地方）你应该指定updateFile为你的其他片段。所以当调用onButtonClick时，它会调用其他片段的方法。

来源

2013-11-26 08:05:49

我编辑了我的问题。现在我收到一条新的错误消息。 – user3033922

你要实现你的界面：在您的onCreateView，你可以做

updateFile = new UpdateFile() { 

    public void onButtonClick() { 
    // put your logic inside 
    }  
};

或者你可以创建一个类：

class MyUpdateFile implements UpdateFile { 
     public void onButtonClick() { 
     // put your logic inside 
     } 
}

和assing到updateFile = new MyUpdateFile();

来源

2013-11-26 08:08:20 Blackbelt

我编辑了我的问题。现在我收到一条新的错误消息。 – user3033922

你去哪里在你的代码中分配了updateFile？

指定为updateFile = new UpdateFile();

来源

2013-11-26 08:24:41

想通了......

我需要有这样的MainActivity：

public void onButtonClick() { 
     android.support.v4.app.Fragment f = this.getSupportFragmentManager().findFragmentByTag(getFragmentTag(0)); 
     ((HistoryFragment) f).updateTable(); 
    } 

    private String getFragmentTag(int pos){ 
     return "android:switcher:"+R.id.pager+":"+pos; 
    }

后我加入了onAttach方法我AddFragment，我只需要找到HistoryFragment标签，以请拨打updateTable()方法。

来源

2013-11-26 18:24:12 user3033922

Android NullPointerError按钮单击

回答

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