空指針異常選擇上下文菜單項

時，我有一個項目列表。當我長時間按下某個項目時，我會彈出一個上下文菜單，其中有3個選項可供編輯，刪除並添加到收藏夾中。然而，當我從上下文菜單中選擇第一項，以編輯聯繫人，我得到了以下錯誤：空指針異常選擇上下文菜單項

了java.lang.RuntimeException：無法啓動活動ComponentInfo {com.example.oopca2/com.example.oopca2。 EditActivity}：顯示java.lang.NullPointerException

這是我的代碼：

public class MainActivity extends ListActivity { 

ActionBar ab; 
ContactsListAdapter adapter; 
ContactsDbAdapter dbAdapter; 
List<Contact> contacts; 
Context context; 
private Contact selectedPerson; 

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

    ab = this.getActionBar(); 
    ab.setDisplayShowTitleEnabled(true); 
    ab.setTitle("All Contacts"); 

    dbAdapter = new ContactsDbAdapter(this); 
    dbAdapter.open(); 
    contacts = dbAdapter.getAllContacts(); 
    adapter = new ContactsListAdapter(this, contacts, dbAdapter); 
    this.setListAdapter(adapter); 
    registerForContextMenu(this.getListView()); 

    context = this.getApplicationContext(); 

} 

@Override 
protected void onResume() { 
    super.onResume(); 
    adapter.updateList(); 
} 

@Override 
protected void onListItemClick(ListView l, View v, int position, long id) { 
    Contact c = contacts.get(position); 
    Toast.makeText(this, c.getName().toString() + " Clicked!", Toast.LENGTH_SHORT).show(); 
} 

//Context menu 
@Override 
public void onCreateContextMenu(ContextMenu menu, View v,ContextMenuInfo menuInfo) { 
    AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo; 
    this.selectedPerson = contacts.get(info.position); 
    MenuInflater mi = getMenuInflater(); 
    mi.inflate(R.menu.activity_context, menu); 
    menu.setHeaderIcon(R.drawable.setting); 
    menu.setHeaderTitle(this.selectedPerson.getName().toString() + " - Options"); 
} 

@Override 
public boolean onContextItemSelected(MenuItem item) {

AdapterView.AdapterContextMenuInfo信息=（AdapterView.AdapterContextMenuInfo）item.getMenuInfo（）;

long rowId = (info.id); 

    switch(item.getItemId()){ 
    case R.id.menu_edit: 
     Toast.makeText(this, "Edit " + rowId, Toast.LENGTH_SHORT).show(); 
     Intent i = new Intent(getApplicationContext(), EditActivity.class); 
     i.putExtra("row", rowId); 
     startActivity(i); 

     return true; 
    case R.id.menu_delete: 
     Toast.makeText(this, "Delete " + rowId , Toast.LENGTH_SHORT).show(); 
     dbAdapter.deleteContact(rowId); 
     return true; 

    case R.id.menu_favs: 
     Toast.makeText(this, "Added to Favourites!" + rowId, Toast.LENGTH_SHORT).show(); 

     return true; 
    } 

    return false; 
} 

//Options menu 
@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 

    switch(item.getItemId()){ 
    case R.id.menu_add: 
     Toast.makeText(this, "Add Contact", Toast.LENGTH_SHORT).show(); 
     Intent i = new Intent(context, AddActivity.class); 
     startActivity(i); 
     return true; 

    case R.id.menu_fav: 
     Toast.makeText(this, "View Favourites", Toast.LENGTH_SHORT).show(); 
     return true; 
    } 

    return false; 
}

}

這是EditActivity.class：

public class EditActivity extends Activity{ 

EditText name; 
EditText number; 
EditText email; 
CheckBox fav; 
ActionBar ab; 
Button updateBtn; 
ContactsDbAdapter dbAdapter; 
Contact c; 
Intent i; 
Long rowId; 
boolean favourite; 

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

    ab = this.getActionBar(); 
    ab.setTitle("Edit Contact"); 

    dbAdapter.open(); 

    i = getIntent(); 
    rowId = i.getExtras().getLong("row"); 
    c = dbAdapter.getContact(rowId); 

    name = (EditText)findViewById(R.id.editText1); 
    number = (EditText)findViewById(R.id.editText2); 
    email = (EditText)findViewById(R.id.editText3); 
    fav = (CheckBox)findViewById(R.id.checkBox1); 


    name.setText(c.getName().toString()); 
    number.setText(c.getNumber().toString()); 
    email.setText(c.getEmail().toString()); 
    fav.setChecked(c.getFavourite()); 

    updateBtn = (Button)findViewById(R.id.editBtn); 
    updateBtn.setOnClickListener(new View.OnClickListener() { 

     @Override 
     public void onClick(View v) { 

      if(fav.isChecked()){ 
       favourite = true; 
      }else{ 
       favourite = false; 
      } 

      dbAdapter.updateContact(name.getText().toString(), number.getText().toString(), email.getText().toString(), favourite, rowId); 
      dbAdapter.close(); 
      finish(); 
     } 
    }); 
} 

//Options menu 
    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.activity_main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 

     switch(item.getItemId()){ 
     case R.id.menu_add: 
      Toast.makeText(this, "Add Contact", Toast.LENGTH_SHORT).show(); 
      Intent i = new Intent(getApplicationContext(), AddActivity.class); 
      startActivity(i); 
      return true; 

     case R.id.menu_fav: 
      Toast.makeText(this, "View Favourites", Toast.LENGTH_SHORT).show(); 
      return true; 
     } 

     return false; 
    }

}

我不知道我要去的地方錯了。任何幫助將非常感激！謝謝。

LOG：

01-18 23:48:16.319: E/AndroidRuntime(23708): FATAL EXCEPTION: main 
01-18 23:48:16.319: E/AndroidRuntime(23708): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.oopca2/com.example.oopca2.EditActivity}: java.lang.NullPointerException 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread.access$600(ActivityThread.java:139) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.os.Handler.dispatchMessage(Handler.java:99) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.os.Looper.loop(Looper.java:154) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread.main(ActivityThread.java:4944) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at java.lang.reflect.Method.invokeNative(Native Method) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at java.lang.reflect.Method.invoke(Method.java:511) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at dalvik.system.NativeStart.main(Native Method) 
01-18 23:48:16.319: E/AndroidRuntime(23708): Caused by: java.lang.NullPointerException 
01-18 23:48:16.319: E/AndroidRuntime(23708): at com.example.oopca2.EditActivity.onCreate(EditActivity.java:50) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.Activity.performCreate(Activity.java:4531) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071) 
01-18 23:48:16.319: E/AndroidRuntime(23708): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150) 
01-18 23:48:16.319: E/AndroidRuntime(23708): ... 11 more

edit_activity.xml

<RelativeLayout 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" 
android:layout_margin="20dp" 
tools:context=".EditActivity" > 

<CheckBox 
    android:id="@+id/checkBox1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_below="@+id/editText3" 
    android:layout_marginTop="17dp" 
    android:text="@string/favLabel" /> 

<Button 
    android:id="@+id/editBtn" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentRight="true" 
    android:layout_below="@+id/checkBox1" 
    android:text="@string/editBtn" /> 

<TextView 
    android:id="@+id/textView3" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_below="@+id/editText2" 
    android:layout_marginTop="22dp" 
    android:text="@string/emailLabel" /> 

<EditText 
    android:id="@+id/editText1" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignParentTop="true" 
    android:layout_marginTop="16dp" 
    android:layout_toRightOf="@+id/textView2" 
    android:ems="10" 
    android:inputType="textPersonName" /> 

<EditText 
    android:id="@+id/editText2" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignBottom="@+id/textView2" 
    android:layout_alignLeft="@+id/editText1" 
    android:layout_alignParentRight="true" 
    android:ems="10" 
    android:inputType="phone" /> 

<EditText 
    android:id="@+id/editText3" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignBottom="@+id/textView3" 
    android:layout_alignLeft="@+id/editText2" 
    android:layout_alignParentRight="true" 
    android:ems="10" 
    android:inputType="textEmailAddress" > 

</EditText> 

<TextView 
    android:id="@+id/textView2" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_below="@+id/editText1" 
    android:layout_marginTop="22dp" 
    android:text="@string/numberLabel" /> 

<TextView 
    android:id="@+id/textView1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignBottom="@+id/editText1" 
    android:layout_alignParentLeft="true" 
    android:text="@string/nameLabel" />

來源

2013-01-18 Javacadabra

這意味着你有一個空的地方，並嘗試在調用一個函數它。沒有完整的堆棧跟蹤，我們無法幫助您。但完整跟蹤會告訴您問題的文件名，功能和行號。 –

請及時發佈所有的logcat錯誤的習慣，它消除了猜測工作。 – Sam

哪條線是'EditActivity.java：50'？ –

你根本都忘了初始化dbAdapter：

dbAdapter = new ContactsDbAdapter(); // Something like this 
dbAdapter.open();

來源

2013-01-18 23:44:02 Sam

我照你的建議做了，但我仍然得到了NPE。我將我的日誌Cat錯誤添加到了問題中。 – Javacadabra

'產生的原因：在顯示java.lang.NullPointerException com.example.oopca2.EditActivity.onCreate（EditActivity.java:50）'什麼是線50 EditActivity？ – Sam

'name.setText（c.getName（）的toString（））;' – Javacadabra

空指針異常選擇上下文菜單項

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