Question

我不明白出了什么问题？

LIST_ITEM

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


    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:src="@drawable/no_avatar"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/name"
        android:layout_gravity="top|center_horizontal"
        android:layout_marginLeft="10dp"/>

    <CheckBox
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/checkbox"
        android:id="@+id/checkBox"
        android:clickable="true"
        android:paddingLeft="@dimen/abc_action_bar_overflow_padding_start_material"
        android:singleLine="false"
        android:textAppearance="@color/colorAccent"
        android:layout_gravity="right" />
</LinearLayout>

fragment_list

    <android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/rootLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

        <ListView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/listView"
            android:layout_margin="@dimen/activity_vertical_margin"/>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_add_white_24dp"
        app:layout_anchor="@id/listView"
        app:layout_anchorGravity="bottom|right|end"
        app:elevation="6dp"
        app:pressedTranslationZ="12dp"
        app:backgroundTint="@color/colorAccent"
        app:rippleColor="@color/colorPrimary"/>
</android.support.design.widget.CoordinatorLayout>

FragmentList.java

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View v = inflater.inflate(R.layout.fragment_list, container, false);
    fab = (FloatingActionButton) getView().findViewById(R.id.fab);
    listView = (ListView) v.findViewById(R.id.listView);


    //обработка добавления человека - нажатие на fab
    fab.setOnClickListener(new View.OnClickListener() {
        @Override public void onClick(View v) {
            //TODO добавление!!!
            Toast.makeText(v.getContext(), "Новая запись добавлена", Toast.LENGTH_SHORT).show();
        }
    });

    //создание курсора
try{
    SQLiteOpenHelper databaseHelper = new DatabaseHelper(v.getContext());
    SQLiteDatabase db = databaseHelper.getWritableDatabase();
    Cursor cursor = db.query("PEOPLE", new String[] {"_id", "NAME", "CHECKBOX"}, null, null, null, null, null);
    CursorAdapter listAdapter = new SimpleCursorAdapter(v.getContext(), R.layout.list_item, cursor, new String[]{"NAME", "CHECKBOX"}, new int[]{R.id.name, R.id.checkBox}, 0);
        listView.setAdapter(listAdapter);
        //переход к первой записи в курсоре
        if (cursor.moveToFirst()){
            //получение данных из курсора
            nameText = cursor.getString(1);
            isAvatar = (cursor.getInt(2)==1);
            //заполнение чекбокса, тест имени и аватар
            CheckBox checkBox = (CheckBox) v.findViewById(R.id.checkBox);
            TextView textView = (TextView) v.findViewById(R.id.name);
            ImageView image = (ImageView) v.findViewById(R.id.imageView);
            checkBox.setChecked(isAvatar);
            textView.setText(nameText);
            if (checkBox.isChecked()) {
                image.setImageResource(R.drawable.avatar);
            } else image.setImageResource(R.drawable.no_avatar);
        }
    } catch (SQLiteException e){
        Toast.makeText(v.getContext(), "База данных недоступна", Toast.LENGTH_SHORT).show();
    }

        //обработка нажатия по чекбоксу
//        checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener(){
//            @Override
//            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
//                checkBox.isChecked();
//            }
//        });

        return v;
}





//обработка нажатия пункте списка
public void onListItemClick(){

}

//закрытие базы данных и курсора
@Override
public void onDestroy(){
    super.onDestroy();
    cursor.close();
    db.close();
}

}

为什么CheckBox checkBox =（CheckBox）v.findViewById（R.id.checkBox）为空？我尝试了很多变化，但变得愚蠢（（

debug screenshot

Answer 1

您正在膨胀不包含复选框，图像视图或文本视图的fragment_list布局。这就是你得到这个错误的原因。实现这个游标适配器

public class MyCursorAdapter extends CursorAdapter {

    public MyCursorAdapter(Context context, Cursor cursor, int flags) {
        super(context, cursor, 0);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        return LayoutInflater.from(context).inflate(R.layout.mylist_row, parent, false);
    }

    @Override
    public void bindView(View v, Context context, Cursor cursor) {

        if (cursor.moveToFirst()){
            //получение данных из курсора
            nameText = cursor.getString(1);
            isAvatar = (cursor.getInt(2)==1);
            //заполнение чекбокса, тест имени и аватар
            CheckBox checkBox = (CheckBox) v.findViewById(R.id.checkBox);
            TextView textView = (TextView) v.findViewById(R.id.name);
            ImageView image = (ImageView) v.findViewById(R.id.imageView);
            checkBox.setChecked(isAvatar);
            textView.setText(nameText);
            if (checkBox.isChecked()) {
                image.setImageResource(R.drawable.avatar);
            } else image.setImageResource(R.drawable.no_avatar);
        }

    }

}

现在在onCreateview

MyCursorAdapter todoAdapter = new MyCursorAdapter(this.getActivity(), cursor, 0);
        lvItems.setAdapter(todoAdapter);

Answer 2

您正在查看checkBox上的v：CheckBox checkBox = (CheckBox) v.findViewById(R.id.checkBox);但v已分配到fragment_list此处View v = inflater.inflate(R.layout.fragment_list, container, false);但是fragment_list不包含checkBox和，因此v.findViewById(R.id.checkBox)返回null 。当你想使用SimpleCursorAdapter时，你需要创建一个扩展SimpleCursorAdapter的类，然后你可以访问/膨胀getView (final int pos, View view, ViewGroup parent)中的“row-item”布局文件 - 然后你就可以说：CheckBox checkBox = (CheckBox) view.findViewById(R.id.checkBox)。

NullPointerException错误的上下文？

2 个答案: