Question

我创建了一个包含ListView的Fragment，并且我已经创建了一个costumAdapter来填充它。

当我点击ListView上的某个项目时，我在空对象引用上遇到错误。

我点击的项目的位置是正确的，但是当我尝试访问listView的对象时，我收到了错误。

这是我的片段

public class PartiteDisponibiliFragment extends Fragment {


public PartiteDisponibiliFragment() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view =  inflater.inflate(R.layout.fragment_partite_disponibili, container, false);

    final databasehelper databaseHelper = new databasehelper(this.getContext());

    final ListView simpleList = view.findViewById(R.id.ListView01);

    ArrayList<String> list_data = new ArrayList<String>();
    ArrayList<String> list_luogo = new ArrayList<String>();
    ArrayList<String> list_orario = new ArrayList<String>();

    Button btn_addpartita = view.findViewById(R.id.btn_addpartita);

    final Cursor b = databaseHelper.getPartiteDisponibili();
    try {
        while (b.moveToNext()) {

            list_luogo.add(b.getString(0));
            list_orario.add(b.getString(1));
            list_data.add(b.getString(2));
            }
    } finally {
        b.close();
    }

    MyAdapterMatch customAdapter =
            new MyAdapterMatch(this.getContext(),
                    list_luogo, list_orario, list_data);

    simpleList.setAdapter(customAdapter);

    btn_addpartita.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent myIntent = new Intent(getContext(), AddPartitaActivity.class);
            startActivity(myIntent);
        }
    });

    simpleList.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int position, long arg3) {
            Toast.makeText(getContext(), "Foo", Toast.LENGTH_SHORT).show();
            Object o = simpleList.getItemAtPosition(position);

            String s = o.toString();
        }
    });

    return view;
}
}

这是我的costumAdapter

public class MyAdapterMatch extends BaseAdapter {

private Context context;
private int resource;
private ArrayList<String> list_luogo;
private ArrayList<String> list_orario;
private ArrayList<String> list_data;

private LayoutInflater inflter;
//static ArrayList<Integer> selectedAnswers;

MyAdapterMatch(Context applicationContext,
               ArrayList<String> list_luogo,
               ArrayList<String> list_orario,
               ArrayList<String> list_data) {
    this.context = context;
    this.resource = resource;
    this.list_data = list_data;
    this.list_orario = list_orario;
    this.list_luogo = list_luogo;

    // initialize arraylist and add static string for all the questions
    /*selectedAnswers = new ArrayList<>();
    for (int i = 0; i < list_data.size(); i++) {
        selectedAnswers.add(0);
    }*/
    inflter = (LayoutInflater.from(applicationContext));
}

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

@Override
public Object getItem(int i) {
    return null;
}

@Override
public long getItemId(int i) {
    return 0;
}

@SuppressLint("ViewHolder")
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
    view = inflter.inflate(R.layout.partite_item, null);

    // get the reference of TextView and Button's
    TextView tv_data = view.findViewById(R.id.tv_data);
    TextView tv_luogo = view.findViewById(R.id.tv_luogo);
    TextView tv_orario = view.findViewById(R.id.tv_orario);

    tv_data.setText(list_data.get(i));
    tv_luogo.setText(list_luogo.get(i));
    tv_orario.setText(list_orario.get(i));

    return view;
}
}

这是我的partite_item.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">

<TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Luogo:"
    android:textColor="@android:color/black"
    android:textSize="18sp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/textView3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dp"
    android:text="Data:"
    android:textColor="@android:color/black"
    android:textSize="18sp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/textView2" />

<TextView
    android:id="@+id/textView4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dp"
    android:text="Orario:"
    android:textColor="@android:color/black"
    android:textSize="18sp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/textView3" />

<TextView
    android:id="@+id/tv_luogo"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="16dp"
    android:layout_marginStart="16dp"
    android:text="TextView"
    android:textSize="18sp"
    app:layout_constraintStart_toEndOf="@+id/textView2"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/tv_data"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    android:text="TextView"
    android:textSize="18sp"
    app:layout_constraintStart_toEndOf="@+id/textView3"
    app:layout_constraintTop_toBottomOf="@+id/tv_luogo" />

<TextView
    android:id="@+id/tv_orario"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    android:text="TextView"
    android:textSize="18sp"
    app:layout_constraintStart_toEndOf="@+id/textView4"
    app:layout_constraintTop_toBottomOf="@+id/tv_data" />

Answer 1

我认为，这段代码是一个问题：

@Override
public Object getItem(int i) {
return null;
}

Answer 2

你的问题是

@Override
public Object getItem(int i) {
    return null;
}

你正在返回null，而是返回列表位置，即i。

@Override
public long getItemId(int i) {
    return 0;
}

你正在返回null，而是返回id即。，i。

见下面的代码：

    @Override
    public Object getItem(int i) {
        return list_data.get(i);
    }

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

Answer 3

试试这个

将接口插入适配器以进行点击处理。

onItemClickListner onItemClickListner;

public void setOnItemClickListner(CommentsAdapter.onItemClickListner onItemClickListner) {
    this.onItemClickListner = onItemClickListner;
}

public interface onItemClickListner {
    void onClick(Contact contact);//pass your object types.
}

适配器中的

和getView（）。

 outerContiner.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            onItemClickListner.onClick(contact);
        }
    });

，最后将适配器绑定到列表视图中，然后调用下面的代码。

    adapter.setOnItemClickListner(new CommentsAdapter.onItemClickListner() {
        @Override
        public void onClick(Contact contact) {
            // here get click item object data.
        }
    });

listview.getItemAtPosition为null

3 个答案: