Question

我在片段中创建动态按钮时遇到问题。我的xml被称为“home_fragment”，这个布局似乎无法在“rootView”中找到，因为我在这一行抛出了NullPointerException：

RelativeLayout ll = (RelativeLayout)rootView.findViewById(R.id.home_fragment);

我的print语句确认“ll”变量为空。这是否与我使用片段的事实有关，因为这个用于创建动态按钮的代码似乎对其他人有效。 以下是我的代码 ：

public class HomeFragment extends Fragment {

ViewGroup rootContainer;
LayoutInflater rootInflater;
private ButtonCreator bc;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}
// onCreateView
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.home_fragment, container, false);


    rootContainer = container;
    rootInflater = inflater;


    return view;
}

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

}


public interface ButtonCreator{
    void buttonCreator(Drawable drawable, String string);
}


// Create button from icon and image name

// Change Drawable back to BitmapDrawable

public void createButton (Drawable drawable, String applicationName){


    Log.d("tag_name", "createButton");


    try {


        ImageButton btn = new ImageButton(getActivity());

        btn.setImageDrawable(drawable);

        View rootView = rootInflater.inflate(R.layout.home_fragment, rootContainer, false);
        Log.d("tag_name", "RootInflater" +rootInflater);
        Log.d("tag_name", "RootContainer" +rootContainer);
        Log.d("tag_name", "RootView" +rootView);

        RelativeLayout ll = (RelativeLayout)rootView.findViewById(R.id.home_fragment);
        Log.d("tag_name", "RelativeLayout" +ll);

        RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
        ll.addView(btn, lp);

    }

    catch (Exception e){

        System.out.println("Exception is "+e.toString());
        e.printStackTrace();
    }

}

}

这是home_fragment xml：

<?xml version="1.0" encoding="utf-8"?>
<HorizontalScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/home_fragment_scroll">

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center_horizontal"
        android:layout_margin="5dp"
        android:id="@+id/home_fragment"
        >


    </RelativeLayout>

</HorizontalScrollView>

以下是MainActivity：

public class MainActivity extends FragmentActivity implements MenuFragment.OnMenufragListener, HomeFragment.ButtonCreator {


   // called when the activity is first created
   @Override
   public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);


   RepeatTask();
   }


   @Override
   public void onMenufrag(Fragment s) {

   // get body fragment (native method is getFragmentManager)
   HomeFragment fragment = (HomeFragment) getSupportFragmentManager().findFragmentById(R.id.home_fragment);

  // if fragment is not null and in layout, set text, else launch BodyActivity
  if ((fragment!=null)&&fragment.isInLayout()) {
     fragment.getView();
  } else {
     Intent intent = new Intent(this,HomeFragment.class);
     startActivity(intent);
  }

   }


@Override
public void buttonCreator(Drawable d,String a) {
    HomeFragment homeFragment = (HomeFragment)getSupportFragmentManager().getFragments().get(1);
    homeFragment.createButton(d,a);
}


   private void RepeatTask()
   {
  repeatTaskThread = new Thread()
  {
     public void run()
     {
        while (true)
        {


           try {



              String applicationName = "app";
              Drawable draw = getResources().getDrawable(R.drawable.settings_camera);

              buttonCreator(draw, applicationName);


              //createbutton.createButton(bitmapdrawable, applicationName);
              Log.d("tag_name", "Entered Home Fragment");


              //socket.close();


           } catch (Exception e) {


              System.out.println("Exception is "+e.toString());

           }



           try
           {
              // Sleep for 5 seconds
              Thread.sleep(5000);
           }
           catch (Exception e)
           {
              e.printStackTrace();
           }
        }
     };
  };
  repeatTaskThread.start();
   }
}

这是main.xml（片段的排列方式）：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:layout_gravity="center"
    android:orientation="horizontal"
    android:weightSum="1">
    <fragment
        android:id="@+id/menuFragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        class="it.anddev.bradipao.janus.MenuFragment"
        tools:layout="@layout/fr_menu">
    </fragment>


    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_toEndOf="@id/menuFragment"
        android:layout_toRightOf="@id/menuFragment"
        android:layout_below="@+id/my_apps_container"
        android:layout_alignBottom="@id/menuFragment" />

</RelativeLayout>

这是MenuFragment.java（对于fr_menu.xml，假设它只是一个空白的相对布局）：

public class MenuFragment extends Fragment {

// activity listener
private OnMenufragListener menufragListener;



// interface for communication with activity
public interface OnMenufragListener {
    public void onMenufrag(Fragment s);
}

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

// onCreate
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Create App with Body Fragment in display, and be able to replace it with other fragments
    FragmentTransaction ft = getFragmentManager().beginTransaction();
    ft.replace(R.id.container, new HomeFragment()).commit();


}


// onActivityCreated
@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
}

// onCreateView
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fr_menu, container, false);

    return view;
}

// (recommended) method to send command to activity
private void sendBodyTextToActivity(Fragment s) {
    menufragListener.onMenufrag(s);
}
}

这是我的StackTrace

05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus D/tag_name: createButton
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus D/tag_name: RootInflatercom.android.internal.policy.impl.PhoneLayoutInflater@2204b848
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus D/tag_name: RootContainerandroid.widget.FrameLayout{22047268 V.E..... ........ 254,67-772,583 #7f0b006b app:id/container}
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus D/tag_name: RelativeLayoutnull
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus I/System.out: Exception is java.lang.NullPointerException
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus W/System.err: java.lang.NullPointerException
05-04 19:05:40.452 3302-3325/it.anddev.bradipao.janus W/System.err:     at it.anddev.bradipao.janus.HomeFragment.createButton(HomeFragment.java:146)
05-04 19:05:40.462 3302-3325/it.anddev.bradipao.janus W/System.err:     at it.anddev.bradipao.janus.MainActivity.buttonCreator(MainActivity.java:80)
05-04 19:05:40.462 3302-3325/it.anddev.bradipao.janus W/System.err:     at it.anddev.bradipao.janus.MainActivity$1.run(MainActivity.java:166)

Answer 1

所以，首先，这不是你加载片段的方式......它不是一个Activity，所以你不能用片段来启动活动。您需要像FragmentTransaction内部一样使用MenuFragment.onCreate()，但这应该看起来应该是您的活动onCreate()。

 Intent intent = new Intent(this,HomeFragment.class);
 startActivity(intent);

反正，你知道这一行正在返回null

RelativeLayout ll = (RelativeLayout)rootView.findViewById(R.id.home_fragment);

这是由于您重新膨胀片段XML布局造成的，这也可以通过替换此行来完成

View rootView = rootInflater.inflate(R.layout.home_fragment, rootContainer, false);

有了这个

View rootView = getView();

至于获取RelativeLayout，你可以在onCreateView

中完成

private RelativeLayout ll;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.home_fragment, container, false);
    ll = (RelativeLayout) view.findViewById(R.id.home_fragment);
    return view;
}

public void createButton (Drawable drawable, String applicationName){
    // Some code... 

    ll.addView();
}

对于动态按钮创建，RelativeLayout视图为NULL

1 个答案: