在Android Studio中用数据库中的两个表填充ListView

Question

I have two tables. tblsubject and tbltopics. I want to list all the subjects with the number of topics every subject.

getSubject()

public Cursor getAllSubject() {
    String where = null;
    Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null, null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c;
}

countTopics()

public int countTopics(long subjectid) {
    String where = KEY_TOPICSUBJECTID + " = " +  subjectid;
    Cursor c = db.query(true, DATABASE_TABLE2, ALL_KEYS2,
            where, null, null, null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c.getCount();
}

viewList() this is where i populate my listview

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public void viewList() {
    Cursor cursor = myDb.getAllSubject();
    String[] fromFieldNames = new String[]{DBAdapter.KEY_SUBJECTID, DBAdapter.KEY_SUBJECT, DBAdapter.KEY_DATESUBJECT};
    int[] toViewIds = new int[]{R.id.txtViewSubjectId, R.id.txtViewSubject, R.id.txtSubjectDateCreated};
    SimpleCursorAdapter myCursorAdapter;
    myCursorAdapter = new SimpleCursorAdapter(getBaseContext(), R.layout.activity_view_the_list, cursor, fromFieldNames, toViewIds, 0);
    ListView myList = (ListView) findViewById(R.id.listView);
    myList.setAdapter(myCursorAdapter);
}

My problem is how to add the number of topics every subject. I can display the Subjects. Thank you.

Answer 1

You can update your subject SQL statement with a subquery to return the topic count from the database. See https://thoughtbot.com/blog/back-to-basics-sql#sub-queries

On a separate note, I would recommend using your own custom AsyncTask and ArrayAdapter.

https://developer.android.com/guide/topics/ui/layout/recyclerview

This will make your UI more responsive and allow you customize the data access and rendering.

By using a custom adapter you can over ride the getView function to control the result and do additional fetches. For example, lazy loading images into the listview display.

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View v = convertView;
    if (v == null) {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = inflater.inflate(R.layout.subjectitem, null);
    }

    if (position % 2 == 1) {            
        v.setBackgroundColor(Color.rgb(234, 234, 234));  
    } else {
        v.setBackgroundColor(Color.WHITE);  
    }              

    YOURDATAOBJECT p = itemList.get(position);
    TextView name = (TextView) v.findViewById(R.id.name);
    TextView topcount = (TextView) v.findViewById(R.id.topcount);

    //You can run our additional data fetches here and update the UI

Answer 2

You can run a direct raw sql with an UNION from your tables. Something like this:

String select = "Select * FROM table1 UNION Select * FROM table2";

Cursor c = return db.rawQuery(select, new String[]{});