用android stdio写一个简单的购物APP 有商家和用户登录后的两个界面 商家界面可以对商品进行修改查看 用户界面可以对商品进行选择 用数据库连接的详细代码

好的，我可以为您提供一个简单的购物APP的代码示例，基于Android Studio和SQLite数据库。

首先，我们需要创建两个活动：商家活动和用户活动。商家活动包括修改和查看商品的功能，用户活动包括选择商品的功能。

商家活动的主要代码如下：

public class MerchantActivity extends AppCompatActivity {
    private EditText mNameEditText;
    private EditText mPriceEditText;
    private Button mAddButton;
    private ListView mListView;

    private DBHelper mDBHelper;
    private SQLiteDatabase mDatabase;
    private Cursor mCursor;
    private SimpleCursorAdapter mAdapter;

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

        mNameEditText = findViewById(R.id.edit_text_name);
        mPriceEditText = findViewById(R.id.edit_text_price);
        mAddButton = findViewById(R.id.button_add);
        mListView = findViewById(R.id.list_view);

        mDBHelper = new DBHelper(this);
        mDatabase = mDBHelper.getWritableDatabase();

        updateUI();

        mAddButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = mNameEditText.getText().toString();
                String price = mPriceEditText.getText().toString();
                ContentValues values = new ContentValues();
                values.put(DBHelper.COLUMN_NAME, name);
                values.put(DBHelper.COLUMN_PRICE, price);
                mDatabase.insert(DBHelper.TABLE_NAME, null, values);
                updateUI();
            }
        });
    }

    private void updateUI() {
        mCursor = mDatabase.query(DBHelper.TABLE_NAME, null, null, null, null, null, null);
        mAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, mCursor,
                new String[]{DBHelper.COLUMN_NAME, DBHelper.COLUMN_PRICE},
                new int[]{android.R.id.text1, android.R.id.text2}, 0);
        mListView.setAdapter(mAdapter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mDatabase.close();
        mCursor.close();
    }
}

用户活动的主要代码如下：

public class UserActivity extends AppCompatActivity {
    private ListView mListView;

    private DBHelper mDBHelper;
    private SQLiteDatabase mDatabase;
    private Cursor mCursor;
    private SimpleCursorAdapter mAdapter;

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

        mListView = findViewById(R.id.list_view);

        mDBHelper = new DBHelper(this);
        mDatabase = mDBHelper.getReadableDatabase();

        updateUI();

        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                mCursor.moveToPosition(position);
                String name = mCursor.getString(mCursor.getColumnIndex(DBHelper.COLUMN_NAME));
                String price = mCursor.getString(mCursor.getColumnIndex(DBHelper.COLUMN_PRICE));
                Toast.makeText(UserActivity.this, "You selected " + name + " for " + price, Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void updateUI() {
        mCursor = mDatabase.query(DBHelper.TABLE_NAME, null, null, null, null, null, null);
        mAdapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, mCursor,
                new String[]{DBHelper.COLUMN_NAME, DBHelper.COLUMN_PRICE},
                new int[]{android.R.id.text1, android.R.id.text2}, 0);
        mListView.setAdapter(mAdapter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mDatabase.close();
        mCursor.close();
    }
}

接下来，我们需要创建一个数据库帮助器类 DBHelper，用于创建和管理数据库。代码如下：

public class DBHelper extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "shopping.db";
    public static final int DATABASE_VERSION = 1;
    public static final String TABLE_NAME = "items";
    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_NAME = "name";
    public static final String COLUMN_PRICE = "price";

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TABLE_NAME + " (" +
                COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                COLUMN_NAME + " TEXT, " +
                COLUMN_PRICE + " TEXT)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

最后，我们需要在AndroidManifest.xml文件中声明两个活动。

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.shoppingapp">

    <application
        ...>
        <activity android:name=".MerchantActivity" />
        <activity android:name=".UserActivity" />
        ...
    </application>

</manifest>

这就是一个简单的购物APP的代码示例，您可以根据您的需求进行修改和扩展。