Question

我想在Java中将LinearView添加到LinearLayout，但是一旦我访问linlay_container中的LinearLayout make_systematics()，我就会得到一个NullPointerException。我有完全相同的代码用于在LinearLayout中定义LinearLayout和TextView textview_systematics。我可以访问TextView，但不是 LinearLayout。这有什么不对？

这个布局是一个片段，包含在<fragment> - 标签中，以防这可能很重要。

xml文件（fragment_species_systematics.xml）：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id              = "@+id/linlay_fragment_species_systematics"
    android:layout_width    = "match_parent"
    android:layout_height   = "wrap_content"
    android:orientation     = "vertical" >

    <TextView
        android:id              = "@+id/textView_fragment_species_systematics"
        android:layout_width    = "match_parent"
        android:layout_height   = "wrap_content" />

</LinearLayout>

Java文件：

public class Fragment_Species_Systematics extends Fragment {

    LinearLayout    linlay_container;
    TextView        textview_systematics;
    View            view;

    public Fragment_Species_Systematics() {}



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

    return view;
    }



    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        linlay_container     = (LinearLayout) getActivity().findViewById(R.id.linlay_fragment_species_systematics);
        textview_systematics = (TextView)     getActivity().findViewById(R.id.textView_fragment_species_systematics);
    }



    public void make_systematics(String json_systematics) {
        if (textview_systematics.isAttachedToWindow())  {Log.i("DEBUG", "tv is attached");} else {Log.i("DEBUG", "tv is not attached");}
        if (linlay_container.isAttachedToWindow())      {Log.i("DEBUG", "ll is attached");} else {Log.i("DEBUG", "ll is not attached");}
    }
}

Answer 1

想出来，遗憾的是没有找到任何理由为什么我做了以下事情：显然无法访问“全局”LinearLayout。我必须包含另一个LinearLayout并访问那个一个，然后才能工作。

我正在使用的xml文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" >

    <LinearLayout
        android:id                = "@+id/linlay_fragment_species_systematics"
        android:layout_width      = "match_parent"
        android:layout_height     = "wrap_content"
        android:orientation       = "vertical" >

        <TextView
            android:id            = "@+id/textView_fragment_species_systematics"
            android:layout_width  = "match_parent"
            android:layout_height = "wrap_content" />

    </LinearLayout>
</LinearLayout>

可以以相同的方式访问TextView但不能访问LinearLayout

1 个答案: