仅在使用Expandablelistview android studio -sqlite的chlid不为空时显示标头 [英] Display header only when chlid is NOT NULL using Expandablelistview android studio -sqlite

问题描述

我正在尝试创建一个消耗性列表视图，其中标题文本从"Organ features"列中引出，子文本从pharynx列中引出，这是我的数据库结构:

I'm trying to make an expendable list view with the header text being extratced from column "Organ features" and child text is extratced from the pharynx column, this is my database structure:

数据库结构

我希望仅当器官特征的子列表(=咽部的实例)不为NULL时，才将器官特征显示为标头. 这就是我到目前为止所得到的(如您所见，咽部的静脉引流是空的，但仍显示为标题，而我不希望这样):

I want organ features to be displayed as header only if their childlist(= instances from the pharynx colum) are NOT NULL. This is what i got so far (as you see, the venous drainage is empty in pharynx column but still displayed as header, and i dont want that):

来自仿真器的图片

我认为我应该添加一条语句"if(DATABASECHILD_1！= null)"或类似的内容..

i Think i should add a statment " if(DATABASECHILD_1 != null)" or something like that ..

感谢您的帮助！

Database.Java

Database.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

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)));
        }

    }
}

推荐答案

我相信您希望基于以下内容进行查询:-

I believe that you want a query based upon :-

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

这将导致:-

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

To convert this for use by the SQLiteDatabase query method, the code instead of being :-

    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);
    }

• 请注意，上面的代码是内部代码，尚未经过测试，因此可能包含一些错误.
• 请注意，没有尝试将其应用于ExpanableListView，假定适配器已正确处理了Cursor.
• 没有这样的IF语句(如果看到IF，则使用IF ??? EXISTS/NOT EXISTS)，而是WHERE子句，该子句确定要包括哪些行(因此在这种情况下，仅包括WHERE行) Pharynx列不为NULL).
  • 与IF真正等效的是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GROUP BY子句并作用于结果而不是输入行，并且实际上用于后处理，例如您可以使用SELECT * FROM OrganAnatomy GROUP BY _id HAVING Pharynx IS NOT NULL ORDER BY Organ_features;(因为_id将是唯一的，因此每一行都将在其自己的组中).
  • 在这种情况下，使用HAVING子句过分/过于复杂.
  • Note the above code is in-principle code and has not been tested, so may contain some errors.
  • Note no attempt has been made to apply this to the ExpanableListView, it has been assumed that the adapter handles the Cursor appropriately.
  • There is no IF statement as such (IF ??? EXISTS/ NOT EXISTS is where you you see IF used), rather a WHERE clause, which determines what rows are to be included (so in this case only include rows WHERE the Pharynx column IS NOT NULL).
    • The real equivalent to IF is the CASE WHEN .... ELSE .... END AS construct, although this isn't needed and also isn't suitable for this scenario.
    • There is also the HAVING clause but this expects a GROUP BY clause and acts upon the result rather than the input rows and is really used for post processing, e.g. you could have SELECT * FROM OrganAnatomy GROUP BY _id HAVING Pharynx IS NOT NULL ORDER BY Organ_features; (works as _id will be unique so every row will be in it's own group).
    • Using the HAVING clause is overkill/over-complicated in this scenario.

    这篇关于仅在使用Expandablelistview android studio -sqlite的chlid不为空时显示标头的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！