android sqlite数据库检索有问题

Question

i am making a tableview in android where i have 2 columns. The first column is the itemname and second one is itemprice. I have connected everything to the database. I made a good alternative of maiking the itemname column as an autocomplete text view and connecting it to the listview which is further connected to the database (which is hidden). So, i get the itemnames... now i want whenever i add the itemname in the column, the prices from the database of the corresponding item is retrieved automatically to the column ...please help me i am stucked with it from last month

 public Cursor getAllData1() {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor res1 = db.rawQuery("select * from " + Tname, null);
        return res1;
    }

In my main activity

 private void preparedata() {
        list = new ArrayList<String>();
        Cursor res1 = mydb.getAllData1();

        if (res1.getCount() == 0) {
            Toast.makeText(this, "No data in the database", Toast.LENGTH_SHORT).show();
        } else {
            while (res1.moveToNext()) {
                list.add(res1.getString(2));
                adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);
                adapter1 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_2,array);
                listView.setAdapter(adapter);
            }

        }
    }


 --------------------------------------------------------------------------

  autocompletetextview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                                       @Override
                                       public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                                           try {

                                               Cursor res2 = mydb.getAllData1();
                                               if (res2.getCount() == 0) {
                                                   Toast.makeText(shopp.this, "no item added", Toast.LENGTH_SHORT).show();
                                               } else {
                                                   while (res2.moveToNext()) {
                                                       et8.setText(res2.getString(2));
                                                   }

                                                   {

                                                   }
                                               }
                                           } catch (Exception e) {
                                               Toast.makeText(shopp.this, "Oops something went wrong", Toast.LENGTH_SHORT).show();
                                           }
                                       }
                                   });

Answer 1

One of the areas where you are going wrong or needlessly complicating matters is in your onItemClick Listsner.

The following answer is a working example that uses a Cursor adapter ( SimpleCursorAdapter ) and shows both columns Itemname and Itemprice. Additionally clicking on an item Toast all the values and Long Clicking will delete an Item and refresh the ListView.

However Cursor Adapters require a column name _id and it expects this to be the value of the rowid column. The rowid column is a special column that uniquely identifies a row but it is normally hidden. The query in the code that returns the Cursor (method getAllData2 ) makes use of this (basically the select SQL is SELECT rowid AS _id, * FROM the_table ).

As the underlying source is the Cursor, the Cursor positioned for you is available and thus all the values. So there is no need to search you just get the values from the Cursor. Additional the 4th parameter to onItemClick/onItemLongClick is the value in the _id column (the rowid ) and this can be used to find a specific row (in the example onItemLongClick uses this for the deletion of the row).

The Database Helper DBHelper.java :-

public class DBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "mydb";
    public static final int DBVERSION = 1;

    public static final String Tname = "mytable";
    public static final String COL_ITEMNAME = "itemname";
    public static final String COL_ITEMPRICE = "itemprice";

    String crt_tbl = "CREATE TABLE IF NOT EXISTS " + Tname + "(" +
            COL_ITEMNAME + " TEXT UNIQUE," +
            COL_ITEMPRICE + " REAL DEFAULT 0.0" +
            ")";

    public DBHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(crt_tbl);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {

    }

    public long addItem(String itemname, Double itemprice) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues cv = new ContentValues();
        cv.put(COL_ITEMNAME,itemname);
        cv.put(COL_ITEMPRICE, itemprice);
        return db.insert(Tname,null,cv);
    }

    //<<<<<<<<<< NOT USED
    public Cursor getAllData1() {
        SQLiteDatabase db = this.getWritableDatabase();
        return db.rawQuery("select * from " + Tname, null);
    }

    //<<<<<<<<<< ALTERNATIVE USED 
    public Cursor getAllData2() {
        SQLiteDatabase db = this.getWritableDatabase();
        String[] columns = new String[]{"rowid AS " + BaseColumns._ID,"*"}; //<<<<<<<<<< see Note below
        return db.query(Tname,columns,null,null,null,null,null);
    }

    public int deleteItemByRowid(long id) {
        String whereclause = "rowid" + "=?";
        String[] whereargs = new String[]{String.valueOf(id)};
        SQLiteDatabase db = this.getWritableDatabase();
        return db.delete(Tname,whereclause,whereargs);
    }
}

• Note BaseColumns._ID resolves to _id so String[] columns = new String[]{"rowid AS " + BaseColumns._ID,"*"}; creates a 2 element String array the first element has rowid AS _id , the second has * (all columns).

MainActivity.java :-

public class MainActivity extends AppCompatActivity {

    ListView mListView;
    DBHelper mydb;
    Cursor mCsr;
    SimpleCursorAdapter mSCA;
    Context mContext;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mContext = this;
        mListView = this.findViewById(R.id.listview);
        mydb = new DBHelper(this);
        addSomeDataForTesting(); //<<<<<<<<<< Add some test data
        doListView(); //<<<<<<<<<< setup the listview
    }

    private void doListView() {
        mCsr = mydb.getAllData2();
        if (mSCA == null) {
            mSCA = new SimpleCursorAdapter(this,
                    android.R.layout.simple_list_item_2,
                    mCsr,
                    new String[]{
                            DBHelper.COL_ITEMNAME,
                            DBHelper.COL_ITEMPRICE
                    },
                    new int[]{
                            android.R.id.text1,
                            android.R.id.text2
                    },
                    0
            );
            mListView.setAdapter(mSCA);

            // Set the onItemClick Listener
            mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                    Toast.makeText(mContext,
                            "You clicked on " + mCsr.getString(mCsr.getColumnIndex(DBHelper.COL_ITEMNAME)) +
                                    ". The Price is " + String.valueOf(mCsr.getDouble(mCsr.getColumnIndex(DBHelper.COL_ITEMPRICE))) +
                                    ". The rowid is " + String.valueOf(mCsr.getLong(mCsr.getColumnIndex(BaseColumns._ID))) +
                                    ". Alternately the rowid is " + String.valueOf(l), //<<<<<<<<<< l is the value of the column _id
                            Toast.LENGTH_SHORT
                            ).show();
                }
            });
            mListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
                @Override
                public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l) {
                    mydb.deleteItemByRowid(l); //<<<<<<<<< uses the value of the 4th parameter passed which is the value of the _id column (which should be the rowid)
                    doListView();
                    return true;
                }
            });
        } else {
            mCsr = mydb.getAllData2();
            mSCA.swapCursor(mCsr);
        }
    }

    private void addSomeDataForTesting() {
        if (DatabaseUtils.queryNumEntries(mydb.getWritableDatabase(),DBHelper.Tname) < 1) {
            mydb.addItem("Item 1",25.55);
            mydb.addItem("Item 2",50.99);
            mydb.addItem("Item 3", 125.35);
        }
    }
}