Android ListAdapter:NullPointerException异常

此代码适用于基本活动，但不适用于选项卡式活动。 我想将ListView与自定义视图一起使用。 通用代码：

list_row.xml:

<?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">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView2" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView3" />
</LinearLayout>

和我的自定义ListAdapter：

    public class EgyeniAdapter extends BaseAdapter {

        Context context;
        ArrayList<Adat> adatok;

        public EgyeniAdapter(Context context, ArrayList<Adat> adatok) {
            this.context = context;
            this.adatok = adatok;
        }

        @Override
        public int getCount() {
            return adatok.size();
        }

        @Override
        public Object getItem(int position) {
            return adatok.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_row,null); // itt rendelem hozza a saját viewet

            if (convertView != null)
            {
                TextView Cim = (TextView) convertView.findViewById(R.id.textView2);
                TextView Alcim = (TextView) convertView.findViewById(R.id.textView3);

                Adat adatom = adatok.get(position);
                Cim.setText(adatom.getNev());
                Alcim.setText(adatom.getSzakma());

            }
            return convertView;
        }
    }

And it is my MainActivity:

@Override
    protected void onCreate(Bundle savedInstanceState) {
    ...
    betolt();
}

private void betolt()
    {
        ArrayList<Adat> adataim = new ArrayList<>();
        adataim.add(new Adat("Title","Subtitle"));
        adataim.add(new Adat("Title2","Subtitle2"));
        final ListView myList=  (ListView) findViewById(R.id.listView);
        EgyeniAdapter egyeniAdapter = new EgyeniAdapter(this,adataim);

        myList.setAdapter(egyeniAdapter);

    }

---

在

betolt（）

中，您正在寻找一个id为

R.id.ListView

（

final ListView myList=（ListView）findViewById（R.id.ListView）；

）的列表视图，但在您的片段布局中，它有id

android=“@+id/tesztek_ListView”

可能是Sry的重复，我复制了正常的活动betolt（）方法。我在选项卡式活动中使用了它：final ListView myList=（ListView）findviewbyd（R.id.tesztek_ListView）；在我看来：EgyeniaAdapter类是可以的。问题是：myList为空。（我在选项卡式视图中使用fragmant）private void betolt（）{..ListView myList=（ListView）findViewById（R.id.tesztek_ListView）；

    public class EgyeniAdapter extends BaseAdapter {

        Context context;
        ArrayList<Adat> adatok;

        public EgyeniAdapter(Context context, ArrayList<Adat> adatok) {
            this.context = context;
            this.adatok = adatok;
        }

        @Override
        public int getCount() {
            return adatok.size();
        }

        @Override
        public Object getItem(int position) {
            return adatok.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_row,null); // itt rendelem hozza a saját viewet

            if (convertView != null)
            {
                TextView Cim = (TextView) convertView.findViewById(R.id.textView2);
                TextView Alcim = (TextView) convertView.findViewById(R.id.textView3);

                Adat adatom = adatok.get(position);
                Cim.setText(adatom.getNev());
                Alcim.setText(adatom.getSzakma());

            }
            return convertView;
        }
    }

And it is my MainActivity:

@Override
    protected void onCreate(Bundle savedInstanceState) {
    ...
    betolt();
}

private void betolt()
    {
        ArrayList<Adat> adataim = new ArrayList<>();
        adataim.add(new Adat("Title","Subtitle"));
        adataim.add(new Adat("Title2","Subtitle2"));
        final ListView myList=  (ListView) findViewById(R.id.listView);
        EgyeniAdapter egyeniAdapter = new EgyeniAdapter(this,adataim);

        myList.setAdapter(egyeniAdapter);

    }

<FrameLayout 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"
    tools:context="com.example.mpet8.englishtest.Tesztek">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment"
        android:id="@+id/tesztek_label"
        />

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tesztek_listView"
        android:layout_gravity="left|top" />

</FrameLayout>

@Override
    protected void onStart() {

        super.onStart();
        betolt();
    }