安卓Android的便签代码

以下是一个简单的 Android 便签 APP 的代码示例，仅供参考：

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private ListView listView;
    private NotesDB notesDB;
    private SQLiteDatabase dbReader;
    private SimpleCursorAdapter adapter;
    private ImageButton addBtn;

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

        listView = (ListView) findViewById(R.id.list);
        addBtn = (ImageButton) findViewById(R.id.btn_add);
        notesDB = new NotesDB(this);
        dbReader = notesDB.getReadableDatabase();

        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, AddActivity.class);
                startActivity(intent);
            }
        });

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(MainActivity.this, DetailActivity.class);
                intent.putExtra(NotesDB.ID, (int) id);
                startActivity(intent);
            }
        });

        initListView();
    }

    private void initListView() {
        Cursor cursor = dbReader.query(NotesDB.TABLE_NAME, null, null, null, null, null, null);
        adapter = new SimpleCursorAdapter(this, R.layout.item, cursor, new String[] {NotesDB.TITLE, NotesDB.TIME},
                new int[] {R.id.title, R.id.time}, SimpleCursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
        listView.setAdapter(adapter);
    }

    @Override
    protected void onResume() {
        super.onResume();
        Cursor cursor = dbReader.query(NotesDB.TABLE_NAME, null, null, null, null, null, null);
        adapter.changeCursor(cursor);
    }
}

AddActivity.java

public class AddActivity extends AppCompatActivity {

    private EditText title, content;
    private Button saveBtn, cancelBtn;
    private NotesDB notesDB;
    private SQLiteDatabase dbWriter;

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

        title = (EditText) findViewById(R.id.et_title);
        content = (EditText) findViewById(R.id.et_content);
        saveBtn = (Button) findViewById(R.id.btn_save);
        cancelBtn = (Button) findViewById(R.id.btn_cancel);
        notesDB = new NotesDB(this);
        dbWriter = notesDB.getWritableDatabase();

        saveBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ContentValues cv = new ContentValues();
                cv.put(NotesDB.TITLE, title.getText().toString());
                cv.put(NotesDB.CONTENT, content.getText().toString());
                cv.put(NotesDB.TIME, getTime());
                dbWriter.insert(NotesDB.TABLE_NAME, null, cv);
                finish();
            }
        });

        cancelBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }

    private String getTime() {
        SimpleDateFormat format = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
        Date date = new Date();
        String str = format.format(date);
        return str;
    }
}

DetailActivity.java

public class DetailActivity extends AppCompatActivity {

    private EditText title, content;
    private Button deleteBtn, editBtn;
    private NotesDB notesDB;
    private SQLiteDatabase dbWriter;
    private int id;

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

        title = (EditText) findViewById(R.id.et_title);
        content = (EditText) findViewById(R.id.et_content);
        deleteBtn = (Button) findViewById(R.id.btn_delete);
        editBtn = (Button) findViewById(R.id.btn_edit);
        notesDB = new NotesDB(this);
        dbWriter = notesDB.getWritableDatabase();

        id = getIntent().getIntExtra(NotesDB.ID, 0);
        Cursor cursor = dbWriter.query(NotesDB.TABLE_NAME, null, "_id=?", new String[] {String.valueOf(id)}, null, null, null);
        cursor.moveToFirst();
        title.setText(cursor.getString(cursor.getColumnIndex(NotesDB.TITLE)));
        content.setText(cursor.getString(cursor.getColumnIndex(NotesDB.CONTENT)));

        deleteBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dbWriter.delete(NotesDB.TABLE_NAME, "_id=?", new String[] {String.valueOf(id)});
                finish();
            }
        });

        editBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ContentValues cv = new ContentValues();
                cv.put(NotesDB.TITLE, title.getText().toString());
                cv.put(NotesDB.CONTENT, content.getText().toString());
                cv.put(NotesDB.TIME, getTime());
                dbWriter.update(NotesDB.TABLE_NAME, cv, "_id=?", new String[] {String.valueOf(id)});
                finish();
            }
        });
    }

    private String getTime() {
        SimpleDateFormat format = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
        Date date = new Date();
        String str = format.format(date);
        return str;
    }
}

NotesDB.java

public class NotesDB extends SQLiteOpenHelper {

    public static final String TABLE_NAME = "notes";
    public static final String ID = "_id";
    public static final String TITLE = "title";
    public static final String CONTENT = "content";
    public static final String TIME = "time";

    public NotesDB(Context context) {
        super(context, "notes", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE " + TABLE_NAME + "(" + ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + TITLE + " TEXT NOT NULL," + CONTENT + " TEXT NOT NULL," + TIME + " TEXT NOT NULL)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

以上是一个简单的 Android 便签 APP 的代码示例，具体细节可以根据实际情况进行调整和优化。