Question

我想为不同的orietation模式构建具有不同布局的应用程序。所以我建立了我的项目同样做了android教程[example here]。但是有一点不同，当我想要各种方向模式（风景，肖像等）时，本教程创建了不同大小（正常和大）。现在我在方向更改期间得到NullPointerException。这是我的代码：

HeadlinesFragment：

public class HeadlinesFragment extends ListFragment {

   OnHeadlineSelectedListener HeadlinesCallback;
   List<Person> personLista = new ArrayList<Person>();

   public interface OnHeadlineSelectedListener {
        public void onArticleSelected(Person person);
    }

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

        int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
                android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;

        //TESTOWE WYPENIENIE
        for(int i=0; i<10; i++){
            personLista.add(new Person("Imie"+i+"Nazwisko"+i,"email"+i+"@example"+i+".com"));
        }
        String[] niceTime = new String[personLista.size()];
        for(int i=0; i<personLista.size(); i++){
            niceTime[i] = personLista.get(i).getName();
        }
        //KONIEC

        setListAdapter(new ArrayAdapter<String>(getActivity(), layout, niceTime));
    }
    @Override
    public void onStart() {
        super.onStart();

        // When in two-pane layout, set the listview to highlight the selected list item
        // (We do this during onStart because at the point the listview is available.)
        if (getFragmentManager().findFragmentById(R.id.person_view) != null) {
            getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
        }
    }

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);

        try{
            HeadlinesCallback = (OnHeadlineSelectedListener)activity;
        }catch(ClassCastException e){
            throw new ClassCastException(activity.toString()
                    + " have to implement OnHeadlineSelectedListener");
        }
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id){
        HeadlinesCallback.onArticleSelected(personLista.get(position));

        getListView().setItemChecked(position, true);
    }

}

PersonFragment：

public class PersonFragment extends Fragment{
   public static Person person;
   ImageView icon;
   TextView text1;
   TextView text2;
   TextView text3;

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

       if(savedInstanceState != null){
           person = (Person)savedInstanceState.getSerializable("person");
       }

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

       icon = (ImageView)view.findViewById(R.id.icon);
       text1 = (TextView)view.findViewById(R.id.name);
       text2 = (TextView)view.findViewById(R.id.email);
       text3 = (TextView)view.findViewById(R.id.info);

       return view;
    }
    @Override
    public void onStart() {
        super.onStart();

        Bundle args = getArguments();
        if (args != null) {
            person = (Person)args.getSerializable("context");

            text1.setText(person.getName());
            text2.setText(person.getEmail());
            text3.setText("Quisque semper ultricies iaculis. Vestibulum nec metus adipiscing, egestas sem mattis, ornare nulla. Quisque nec nibh nec lacus euismod gravida. Proin at pretium enim. In auctor, nisi sit amet pharetra facilisis, est justo mattis mi, eget mattis tortor ligula non orci. Vestibulum neque augue, elementum vitae aliquam non, condimentum ac dui. Nullam ultricies velit nec diam aliquam, sed lacinia sem eleifend. Quisque quam sapien, sodales id suscipit nec, consequat vel nunc. Quisque eu velit nisi. Donec varius consequat metus, tempor semper tortor ultricies vel. Mauris eget arcu nisi. Proin sit amet dui nisl. Quisque auctor lobortis augue sit amet egestas. Fusce mattis aliquam ante, et bibendum nibh ullamcorper et. Integer ipsum nibh, placerat a felis ut, accumsan rutrum eros. Quisque lacinia facilisis ipsum sed commodo.");
            icon.setImageResource(R.drawable.ic_launcher);

        }else{
            if(person==null){
                person = new Person("Test Testowy", "Testowy@gmail.com");
            }
            updateArticleView(person);
        }
    }
    @Override
    public void onSaveInstanceState(Bundle outState){
        super.onSaveInstanceState(outState);
        outState.putSerializable("person", person);
    }
    public void updateArticleView(Person externalPerson) {
        this.person = externalPerson;

        text1.setText(externalPerson.getName());
        text2.setText(externalPerson.getEmail());
        text3.setText("Quisque semper ultricies iaculis. Vestibulum nec metus adipiscing, egestas sem mattis, ornare nulla. Quisque nec nibh nec lacus euismod gravida. Proin at pretium enim. In auctor, nisi sit amet pharetra facilisis, est justo mattis mi, eget mattis tortor ligula non orci. Vestibulum neque augue, elementum vitae aliquam non, condimentum ac dui. Nullam ultricies velit nec diam aliquam, sed lacinia sem eleifend. Quisque quam sapien, sodales id suscipit nec, consequat vel nunc. Quisque eu velit nisi. Donec varius consequat metus, tempor semper tortor ultricies vel. Mauris eget arcu nisi. Proin sit amet dui nisl. Quisque auctor lobortis augue sit amet egestas. Fusce mattis aliquam ante, et bibendum nibh ullamcorper et. Integer ipsum nibh, placerat a felis ut, accumsan rutrum eros. Quisque lacinia facilisis ipsum sed commodo.");
        icon.setImageResource(R.drawable.ic_launcher);

    }

}

和MainActivity：

public class MainActivity extends FragmentActivity implements OnHeadlineSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if(findViewById(R.id.fragment_container)!=null){

        if (savedInstanceState != null) {
            return;
        }

        getSupportFragmentManager().beginTransaction()
            .add(R.id.fragment_container, new HeadlinesFragment()).commit();

    }


}

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

    PersonFragment fragment = (PersonFragment)getSupportFragmentManager().findFragmentById(R.id.person_view);

    if(fragment!=null){
        fragment.updateArticleView(person);
    }else{
        PersonFragment newFragment = new PersonFragment();

        Bundle args = new Bundle();
        args.putSerializable("context", person);
        newFragment.setArguments(args);

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.fragment_container, newFragment);
        transaction.addToBackStack(null);

        transaction.commit();
    }
}

}

问题：在开始一切都很好，但是当我将方向模式更改为横向（在模拟器ctrl + f12中）并再次返回到portain并从listview中选择一些东西时我得到“遗憾的是应用程序停止了”。

是logcat：

11-02 14:29:03.396: E/AndroidRuntime(802): FATAL EXCEPTION: main
11-02 14:29:03.396: E/AndroidRuntime(802): java.lang.NullPointerException
11-02 14:29:03.396: E/AndroidRuntime(802):  at com.example.friendslist.PersonFragment.updateArticleView(PersonFragment.java:68)
11-02 14:29:03.396: E/AndroidRuntime(802):  at com.example.friendslist.MainActivity.onArticleSelected(MainActivity.java:43)
11-02 14:29:03.396: E/AndroidRuntime(802):  at com.example.friendslist.HeadlinesFragment.onListItemClick(HeadlinesFragment.java:69)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.support.v4.app.ListFragment$2.onItemClick(ListFragment.java:58)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.widget.AdapterView.performItemClick(AdapterView.java:298)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.widget.AbsListView.performItemClick(AbsListView.java:1100)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.widget.AbsListView$PerformClick.run(AbsListView.java:2749)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.widget.AbsListView$1.run(AbsListView.java:3423)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.os.Handler.handleCallback(Handler.java:725)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.os.Handler.dispatchMessage(Handler.java:92)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.os.Looper.loop(Looper.java:137)
11-02 14:29:03.396: E/AndroidRuntime(802):  at android.app.ActivityThread.main(ActivityThread.java:5041)
11-02 14:29:03.396: E/AndroidRuntime(802):  at java.lang.reflect.Method.invokeNative(Native Method)
11-02 14:29:03.396: E/AndroidRuntime(802):  at java.lang.reflect.Method.invoke(Method.java:511)
11-02 14:29:03.396: E/AndroidRuntime(802):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-02 14:29:03.396: E/AndroidRuntime(802):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-02 14:29:03.396: E/AndroidRuntime(802):  at dalvik.system.NativeStart.main(Native Method)

我的主要问题是我总是在寻找像“由...引起”的东西，这里我没有。有人能告诉我哪里有问题吗？

在正常的android示例中，当我将子文件夹的名称从layout-large更改为layout-land时，我遇到了同样的问题。

的活动：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />

person_view：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp" >

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:orientation="horizontal">

    <ImageView
        android:id="@+id/icon"
        android:layout_width="72dp"
        android:layout_height="74dp"
        android:src="@drawable/ic_launcher" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="match_parent" >

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Imie i nazwisko" />
            <TextView
                android:id="@+id/email"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="email@sample.com" />

        </LinearLayout>

    </LinearLayout>

</LinearLayout>

<TextView
    android:id="@+id/info"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:text="info" />

land subfolder中的主要活动：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">

<fragment android:name="com.example.friendslist.HeadlinesFragment"
          android:id="@+id/headlines_fragment"
          android:layout_weight="1"
          android:layout_width="0dp"
          android:layout_height="match_parent" />

<fragment android:name="com.example.friendslist.PersonFragment"
          android:id="@+id/person_view"
          android:layout_weight="2"
          android:layout_width="0dp"
          android:layout_height="match_parent" />

Answer 1

好的，在解决这个问题之后，我找到了解决方案，我将onArticleSelected方法中的条件从(fragment!=null)更改为findViewById(R.id.fragment_container)。我不知道为什么，在定位改变片段仍然存在之后，也许有人可以解释我。

编辑：//如果有人想要取向定位，再次确定某些元素等于null，你可以更简单，例如：getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE

方向更改期间NullPointerException

1 个答案: