android studio增删改查代码

以下是一个简单的Android Studio笔记应用程序的增删改查代码示例：

1. 创建一个Note类，包含笔记的标题和内容：

public class Note {
    private int id;
    private String title;
    private String content;

    public Note() {
    }

    public Note(int id, String title, String content) {
        this.id = id;
        this.title = title;
        this.content = content;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

2. 创建一个NoteDatabaseHelper类，用于管理SQLite数据库：

public class NoteDatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "notes.db";
    private static final int DATABASE_VERSION = 1;

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE notes (_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, content TEXT);");
    }

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

3. 创建一个NoteAdapter类，用于显示笔记列表：

public class NoteAdapter extends RecyclerView.Adapter<NoteAdapter.NoteViewHolder> {
    private List<Note> mNotes;
    private OnItemClickListener mListener;

    public interface OnItemClickListener {
        void onItemClick(Note note);
    }

    public NoteAdapter(List<Note> notes, OnItemClickListener listener) {
        mNotes = notes;
        mListener = listener;
    }

    @Override
    public NoteViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_note, parent, false);
        return new NoteViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(NoteViewHolder holder, int position) {
        final Note note = mNotes.get(position);
        holder.titleTextView.setText(note.getTitle());
        holder.contentTextView.setText(note.getContent());
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mListener.onItemClick(note);
            }
        });
    }

    @Override
    public int getItemCount() {
        return mNotes.size();
    }

    public static class NoteViewHolder extends RecyclerView.ViewHolder {
        public TextView titleTextView;
        public TextView contentTextView;

        public NoteViewHolder(View itemView) {
            super(itemView);
            titleTextView = (TextView) itemView.findViewById(R.id.title_text_view);
            contentTextView = (TextView) itemView.findViewById(R.id.content_text_view);
        }
    }
}

4. 创建一个NoteActivity类，用于显示笔记列表和笔记详细信息：

public class NoteActivity extends AppCompatActivity {
    private NoteDatabaseHelper mDbHelper;
    private List<Note> mNotes;
    private RecyclerView mRecyclerView;
    private NoteAdapter mAdapter;

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

        mDbHelper = new NoteDatabaseHelper(this);

        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));

        mNotes = getAllNotes();
        mAdapter = new NoteAdapter(mNotes, new NoteAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(Note note) {
                Intent intent = new Intent(NoteActivity.this, NoteDetailActivity.class);
                intent.putExtra("note_id", note.getId());
                startActivity(intent);
            }
        });

        mRecyclerView.setAdapter(mAdapter);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(NoteActivity.this, NoteDetailActivity.class);
                startActivity(intent);
            }
        });
    }

    @Override
    protected void onResume() {
        super.onResume();
        mNotes = getAllNotes();
        mAdapter.notifyDataSetChanged();
    }

    private List<Note> getAllNotes() {
        List<Note> notes = new ArrayList<>();
        SQLiteDatabase db = mDbHelper.getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM notes", null);
        if (cursor.moveToFirst()) {
            do {
                int id = cursor.getInt(cursor.getColumnIndex("_id"));
                String title = cursor.getString(cursor.getColumnIndex("title"));
                String content = cursor.getString(cursor.getColumnIndex("content"));
                Note note = new Note(id, title, content);
                notes.add(note);
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return notes;
    }
}

5. 创建一个NoteDetailActivity类，用于编辑或添加笔记：

public class NoteDetailActivity extends AppCompatActivity {
    private NoteDatabaseHelper mDbHelper;
    private EditText mTitleEditText;
    private EditText mContentEditText;
    private int mNoteId = -1;

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

        mDbHelper = new NoteDatabaseHelper(this);

        mTitleEditText = (EditText) findViewById(R.id.title_edit_text);
        mContentEditText = (EditText) findViewById(R.id.content_edit_text);

        Intent intent = getIntent();
        if (intent.hasExtra("note_id")) {
            mNoteId = intent.getIntExtra("note_id", -1);
            Note note = getNoteById(mNoteId);
            mTitleEditText.setText(note.getTitle());
            mContentEditText.setText(note.getContent());
        }
    }

    public void onSaveButtonClick(View view) {
        String title = mTitleEditText.getText().toString();
        String content = mContentEditText.getText().toString();
        if (title.isEmpty() || content.isEmpty()) {
            Toast.makeText(this, "请填写标题和内容", Toast.LENGTH_SHORT).show();
            return;
        }
        if (mNoteId == -1) {
            addNoteToDatabase(title, content);
        } else {
            updateNoteInDatabase(mNoteId, title, content);
        }
        finish();
    }

    private Note getNoteById(int id) {
        SQLiteDatabase db = mDbHelper.getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM notes WHERE _id = ?", new String[]{String.valueOf(id)});
        Note note = null;
        if (cursor.moveToFirst()) {
            String title = cursor.getString(cursor.getColumnIndex("title"));
            String content = cursor.getString(cursor.getColumnIndex("content"));
            note = new Note(id, title, content);
        }
        cursor.close();
        db.close();
        return note;
    }

    private void addNoteToDatabase(String title, String content) {
        SQLiteDatabase db = mDbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("title", title);
        values.put("content", content);
        db.insert("notes", null, values);
        db.close();
    }

    private void updateNoteInDatabase(int id, String title, String content) {
        SQLiteDatabase db = mDbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("title", title);
        values.put("content", content);
        db.update("notes", values, "_id = ?", new String[]{String.valueOf(id)});
        db.close();
    }
}

希望这些示例代码对您有所帮助！