仅当使用 Expandablelistview android studio -sqlite chlid 不为 NULL 时显示标题

Question

我正在尝试制作一个消耗性列表视图，其中标题文本从“器官特征”列中提取，子文本从 pharynx 列中提取，这是我的数据库结构：

Database structure

我希望器官特征仅在其子列表（= 咽列中的实例）不为空时才显示为标题。 这是我目前得到的（如你所见，咽列中的静脉引流是空的，但仍显示为标题，我不希望这样）：

picture from the emulator

我认为我应该添加一个语句“if(DATABASECHILD_1 != null)”或类似的东西..

感谢您的帮助！

数据库.Java

package ma.ac.iav.learn;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class Database {
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "URTdd.db";
    private static final String DATABASE_TABLE = "OrganAnatomy";
    public static final String DATABASE_ID = "_id";
    public static final String DATABASE_GROUP_1 = "Organ_features";
    public static final String DATABASE_CHILD_1 = "Pharynx";
    private final Context mContext;
    private DatabaseHelper mDatabaseHelper;
    private SQLiteDatabase mDB;

    public Database(Context context) {
        mContext = context;
    }

    public void open() {
        mDatabaseHelper = new DatabaseHelper(mContext, DATABASE_NAME, null, DATABASE_VERSION);
        mDB = mDatabaseHelper.getWritableDatabase();
    }


    public void close() {
        if (mDatabaseHelper != null) mDatabaseHelper.close();
    }

    public Cursor getDatabase() {
            return mDB.query(DATABASE_TABLE, null, null, null, null, null, DATABASE_GROUP_1);
    }

    public Cursor getID(long rowID) {
            return mDB.query(DATABASE_TABLE, null, "_id" + " = "
                + rowID, null, null, null, null);

    }

    public class DatabaseHelper extends SQLiteAssetHelper {

        public DatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
            super(context, name, factory, version);

        }
    }


}

MainActivity.java

package ma.ac.iav.learn;

import android.content.Context;
import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;
import android.widget.SimpleCursorTreeAdapter;

public class MainActivity extends AppCompatActivity {
    ExpandableListView expandableListView;
    Database mDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
             /*
        "Called when the database has been opened."
        https://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html#onOpen(android.database.sqlite.SQLiteDatabase)
         */
        mDatabase = new Database(this);
        mDatabase.open();

        /*
        "This interface provides random read-write access to the result set returned by a database query."
        https://developer.android.com/reference/android/database/Cursor.html
         */

        Cursor cursor = mDatabase.getDatabase();
        startManagingCursor(cursor);

        /*
        "A list of column names that will be used to display the data for a group."
        "The group views (from the group layouts) that should display column in the "from" parameter."
        "A list of column names that will be used to display the data for a child."
        "The resource identifier of a layout file that defines the views for a child."
        https://developer.android.com/reference/android/widget/SimpleCursorTreeAdapter.html#SimpleCursorTreeAdapter(android.content.Context, android.database.Cursor, int, java.lang.String[], int[], int, java.lang.String[], int[])
         */

        String[] groupFrom = {
                Database.DATABASE_GROUP_1,
        };

        int[] groupTo = {
                R.id.group1,
        };
        String[] childFrom = new String[]{
                Database.DATABASE_CHILD_1,
        };
        int[] childTo = {
                R.id.child1,
        };

        /*
        "An easy adapter to map columns from a cursor to TextViews or ImageViews defined in an XML file."
        https://developer.android.com/reference/android/widget/SimpleCursorTreeAdapter.html
        */
        SimpleCursorTreeAdapter simplecursortreeAdapter = new ExpandableListViewAdapter(
                this,
                cursor,
                R.layout.list_group,
                groupFrom,
                groupTo,
                R.layout.list_child,
                childFrom,
                childTo
        );

        /*
        "Finds a view that was identified by the android:id XML attribute that was processed in onCreate(Bundle)."
        "Sets the adapter that provides data to this view."
        https://developer.android.com/reference/android/app/Activity.html#findViewById(int)
        https://developer.android.com/reference/android/widget/ExpandableListView.html#setAdapter(android.widget.ExpandableListAdapter)
         */
        expandableListView = findViewById(R.id.expandableListview);
        expandableListView.setAdapter(simplecursortreeAdapter);

    }

    /*
    "Closes the Cursor, releasing all of its resources and making it completely invalid."
    https://developer.android.com/reference/android/database/Cursor.html#close()
     */
    protected void onDestroy() {
        super.onDestroy();
        mDatabase.close();
    }

    private class ExpandableListViewAdapter extends SimpleCursorTreeAdapter {
        private ExpandableListViewAdapter(
                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);
        }

        /*
        "Gets the Cursor for the children at the given group."
        https://developer.android.com/reference/android/widget/CursorTreeAdapter.html#getChildrenCursor(android.database.Cursor)
         */
        protected Cursor getChildrenCursor(Cursor groupCursor) {
            return mDatabase.getID(groupCursor.getInt(groupCursor.getColumnIndex(Database.DATABASE_ID)));
        }

    }
}

Answer 1

我相信您需要基于以下内容的查询：-

SELECT * FROM OrganAnatomy WHERE Pharynx IS NOT NULL ORDER BY Organ_features;

这将导致：-

要将其转换为SQLiteDatabase query 方法使用，代码而不是：-

    public Cursor getDatabase() {
        return mDB.query(DATABASE_TABLE, null, null, null, null, null, DATABASE_GROUP_1);
    }

可能是：-

    public Cursor getDatabase() {
        String whereclause = DATABASE_CHILD_1 + " IS NOT NULL";
        return mDB.query(DATABASE_TABLE, null, whereclause, null, null, null, DATABASE_GROUP_1);
    }

• 注意以上代码为in-principal code，未经测试，可能存在一些错误。
• 请注意，没有尝试将其应用于 ExpanableListView，假设适配器正确处理了光标。
• 没有这样的 IF 语句（IF ??? EXISTS/NOT EXISTS 是您看到使用 IF 的地方），而是一个 WHERE 子句，它确定要包含哪些行（因此在这种情况下只包含行 WHERE Pharynx 列不为空）。
  • 真正等效于 IF 的是 CASE WHEN .... ELSE .... END AS 构造，尽管这不是必需的，也不适合这种情况。
  • 还有 HAVING 子句，但这需要一个 GROUP BY 子句并作用于结果而不是输入行，并且真正用于后处理，例如您可以拥有SELECT * FROM OrganAnatomy GROUP BY _id HAVING Pharynx IS NOT NULL ORDER BY Organ_features;（作为_id 工作将是唯一的，因此每一行都将在它自己的组中）。
  • 在这种情况下，使用 HAVING 子句过于矫枉过正/过于复杂。