如何为下拉元素制作自定义视图

有一个下拉列表ExpandableListView，里面显示了国家和他们的景点。标题是国家/地区，当您单击国家/地区时，会打开一个包含景点的下拉列表。

如何为这些下拉元素本身制作自定义视图。

为下拉列表中的每个项目创建标记

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

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="5dp">

        <de.hdodenhof.circleimageview.CircleImageView
            xmlns:app="http://schemas.android.com/apk/res-auto"
            android:id="@+id/img"
            android:src="@drawable/bg"
            app:civ_border_color="#FF000000"
            android:layout_width="42dp"
            android:layout_height="42dp"
            android:scaleType="centerCrop" />

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:paddingLeft="8dp"
            android:paddingRight="8dp">

            <TextView
                android:text=""
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:id="@+id/txtTitle"
                android:layout_weight="1"
                android:gravity="left|center" />

            <TextView
                android:text=""
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:id="@+id/txtHistory"
                android:layout_weight="1"
                android:singleLine="true" />
        </LinearLayout>

        <ImageButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:srcCompat="@drawable/icon_star_outline_black"
            android:id="@+id/btnfavorite"
            android:background="@drawable/white_button"
            android:focusable="false"
            android:onClick="onFavoriteClick" />

    </LinearLayout>
</LinearLayout>

数据库助手类

public class DBHeler extends SQLiteOpenHelper {
    private static String DB_PATH;
    private static final String DATABASE_NAME = "mydb.db";
    private static final int DATABASE_VERSION = 1;
    public SQLiteDatabase database;
    private Context myContext;

    public DBHeler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        this.myContext = context;
        try {
            //получаем путь до БД вместе с именем.
            DB_PATH = myContext.getDatabasePath(DATABASE_NAME).toString();
            createDataBase();
            openDataBase();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public Cursor getCategoryData() {
        return this.getReadableDatabase().query(Contract.Entry.TABLE_COUNTRY, null, null, null, null, null, null);
    }

    public Cursor getSubCategoryData(long categoryID) {
        return this.getReadableDatabase().query(Contract.Entry.TABLE_DOST, null, Contract.Entry._ID + " = "
                + categoryID, null, null, null, null);
    }

    public void createDataBase() throws IOException {

        boolean dbExist = checkDataBase();

        if (!dbExist) {
            this.getReadableDatabase();
            try {
                copyDataBase();
            }
            catch (IOException e) {
                throw new Error("Error copying database");
            }
        }
    }

    private boolean checkDataBase(){
        SQLiteDatabase checkDB = null;
        try {

            checkDB = SQLiteDatabase.openDatabase(DB_PATH, null, SQLiteDatabase.OPEN_READONLY);
        }
        catch (SQLiteException e) {
            // база не существует
        }
        if (checkDB != null) {
            checkDB.close();
        }
        return checkDB != null;
    }

    private void copyDataBase() throws IOException {
        InputStream myInput = myContext.getAssets().open(DATABASE_NAME);

        String outFileName = DB_PATH;

        OutputStream myOutput = new FileOutputStream(outFileName);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer, 0, length);
        }

        myOutput.flush();
        myOutput.close();
        myInput.close();
    }

    public void openDataBase() throws SQLException {
        database = SQLiteDatabase.openDatabase(DB_PATH, null, SQLiteDatabase.OPEN_READWRITE);
    }

    @Override
    public synchronized void close() {
        if(database != null)
            database.close();
        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

主要活动类

public class MainActivity extends AppCompatActivity {

    ExpandableListView elvMain;
    DBHeler db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        db = new DBHeler(this);

        Cursor categoryData = db.getCategoryData();

        startManagingCursor(categoryData);

        String[] groupFrom = { Contract.Entry.COLUMN_NAME };
        int[] groupTo = { android.R.id.text1 };

        String[] childFrom = { Contract.Entry.COLUMN_NAME };
        int[] childTo = { android.R.id.text1  };

        SimpleCursorTreeAdapter sctAdapter = new MyAdapter(this, categoryData,
                android.R.layout.simple_expandable_list_item_1, groupFrom,
                groupTo, android.R.layout.simple_list_item_1, childFrom,
                childTo);

        elvMain = (ExpandableListView) findViewById(R.id.list);

        elvMain.setAdapter(sctAdapter);
    }

    public class MyAdapter extends SimpleCursorTreeAdapter {

        public MyAdapter(Context context, Cursor cursor, int groupLayout,
                         String[] groupFrom, int[] groupTo, int childLayout,
                         String[] childFrom, int[] childTo) {
            super(context, cursor, groupLayout, groupFrom, groupTo,
                    childLayout, childFrom, childTo);
        }

        protected Cursor getChildrenCursor(Cursor groupCursor) {
            int idColumn = groupCursor.getColumnIndex(Contract.Entry._ID);
            return db.getSubCategoryData(groupCursor.getInt(idColumn));
        }
    }
}

Contract 类，描述字段和列名

public class Contract {
    private Contract() {
    };

    public static final class Entry implements BaseColumns {
        public final static String TABLE_DOST = "dost";
        public final static String TABLE_COUNTRY = "country";

        public final static String _ID = BaseColumns._ID;
        public final static String COLUMN_NAME = "name";
        public final static String COLUMN_OTHER = "other";
        public final static String COLUMN_HISTORY = "history";
        public final static String COLUMN_IMAGE = "image";
        public final static String COLUMN_COUNTRY = "name";
        public final static String COLUMN_COUNTRYID = "countryid";
        public final static String COLUMN_FAVORITES = "favorites";
    }
}