Android，findViewById返回null

Question

我正在为Android编写一些代码，问题在于，当我调用findViewById时它返回null，我不明白为什么！我从昨天开始一直在浪费我的大脑，但我无法弄清楚解决方案。目标是将布局设置为listView的标题。这里是我的代码，分别为我的头和我的网页：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/header" 
    android:orientation="horizontal" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_marginBottom="5dp"> 

    <TextView 
     android:text="@string/bydistance" 
     android:layout_gravity="left" 
     android:layout_width="0dp" 
     android:layout_weight="1" 
     android:layout_height="wrap_content" 
     android:textSize="13dp" 
     android:gravity="center_horizontal"/> 

    <TextView 
     android:text="@string/byactivity" 
     android:layout_gravity="right" 
     android:layout_width="0dp" 
     android:layout_weight="1" 
     android:layout_height="wrap_content" 
     android:textSize="13dp" 
     android:gravity="center_horizontal"/> 

</LinearLayout> 

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
      android:orientation="vertical" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:background="#ff0000" 
    > 

    <ListView 
     android:id="@+id/parkList" 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent" 
     android:divider="@android:color/transparent" 
     android:dividerHeight="5.0dp"> 
    </ListView> 

</LinearLayout> 

在这里，我的代码，我叫addheaderView：

public class NearMeFragment extends Fragment implements View.OnClickListener{ 

private FragmentManager fragmentManager; 

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

@Override 
public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedBundle) { 
    View v = inflater.inflate(R.layout.park_list, container, false); 

    //TODO remove 
    make_test(v, container); 

    return v; 
} 

public void openTest(View view){ 
    new LiveComment().show(getChildFragmentManager(), "dialog"); 
} 

public void onClick(View view){ 
    if (fragmentManager == null) 
     fragmentManager = getChildFragmentManager(); 
    //if (view.getId() == R.id.test){ 
     fragmentManager.beginTransaction().add(new LiveComment(), "livecomment").commit(); 
} 

private void make_test(View v, ViewGroup container) { 

    ListView listView = (ListView) v.findViewById(R.id.parkList); 
    Park[] list = new Park[3]; 
    list[0] = new Park("parco a", "acquasparta", false, false, 1, 2, 3); 
    list[1]=new Park("parco b", "perugia", false, false, 1, 2, 3); 
    list[2]=new Park("parco b", "perugia", false, false, 1, 2, 3); 
    ParkListAdapter adapter = new ParkListAdapter(v.getContext(), R.layout.small_park_container,list); 
    LinearLayout header = (LinearLayout) container.findViewById(R.id.header); 
    listView.addHeaderView(header); 
    listView.setAdapter(adapter); 

} 
} 

误差以

listView.addHeaderView(header) 

Answer 1

R.id.header是给定里面v不在里面container。

变化

LinearLayout header = (LinearLayout) container.findViewById(R.id.header); 

与

LinearLayout header = (LinearLayout) v.findViewById(R.id.header); 

有关的ViewGroup容器医生说：

如果非空，这是父视图，该片段的UI应该是 附加到。片段不应该添加视图本身，但可以使用 来生成视图的LayoutParams。

编辑：既然你的头的看法是在另一个版面您可以充气太：

@Override 
public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedBundle) { 
    View v = inflater.inflate(R.layout.park_list, container, false); 
    View header = inflater.inflate(R.layout.headerlayout, null); 
    //TODO remove 
    make_test(v, header); 

    return v; 
} 

和

private void make_test(View v, View header) { 

    // your code 

    // you have to remove LinearLayout header = (LinearLayout) container.findViewById(R.id.header); 
    listView.addHeaderView(header); 
    listView.setAdapter(adapter); 

}