Android studio设计备忘录，要求实现增删改查功能的代码

以下是一个简单的 Android Studio 设计备忘录的增删改查功能的代码：

1. 创建一个新的 Android Studio 项目
2. 在 activity_main.xml 中添加一个 RecyclerView 和一个 FloatingActionButton
3. 创建一个新的 Java 类，并将其命名为 Memo
4. 在 Memo 类中添加以下代码：

public class Memo {
    private int id;
    private String title;
    private String content;
    private String date;

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

    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;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }
}

5. 创建一个新的 Java 类，并将其命名为 MemoAdapter
6. 在 MemoAdapter 类中添加以下代码：

public class MemoAdapter extends RecyclerView.Adapter<MemoAdapter.MemoViewHolder> {

    private ArrayList<Memo> memos;
    private Context context;

    public MemoAdapter(ArrayList<Memo> memos, Context context) {
        this.memos = memos;
        this.context = context;
    }

    @NonNull
    @Override
    public MemoViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.memo_item, parent, false);
        return new MemoViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MemoViewHolder holder, int position) {
        holder.title.setText(memos.get(position).getTitle());
        holder.content.setText(memos.get(position).getContent());
        holder.date.setText(memos.get(position).getDate());
    }

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

    public class MemoViewHolder extends RecyclerView.ViewHolder {
        TextView title, content, date;

        public MemoViewHolder(@NonNull View itemView) {
            super(itemView);
            title = itemView.findViewById(R.id.title);
            content = itemView.findViewById(R.id.content);
            date = itemView.findViewById(R.id.date);
        }
    }
}

7. 在 res/layout 文件夹中创建一个名为 memo_item.xml 的新布局文件，并添加以下代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:textSize="16sp" />

    <TextView
        android:id="@+id/date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        android:textStyle="italic" />

</LinearLayout>

8. 在 MainActivity.java 中添加以下代码：

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private MemoAdapter memoAdapter;
    private ArrayList<Memo> memos = new ArrayList<>();
    private FloatingActionButton addMemoButton;

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

        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        memoAdapter = new MemoAdapter(memos, this);
        recyclerView.setAdapter(memoAdapter);

        addMemoButton = findViewById(R.id.addMemoButton);
        addMemoButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, AddMemoActivity.class);
                startActivityForResult(intent, 1);
            }
        });

        loadMemos();
    }

    private void loadMemos() {
        memos.clear();
        Cursor cursor = getContentResolver().query(MemoContract.MemoEntry.CONTENT_URI,
                null, null, null, null);

        if (cursor.moveToFirst()) {
            do {
                int id = cursor.getInt(cursor.getColumnIndex(MemoContract.MemoEntry._ID));
                String title = cursor.getString(cursor.getColumnIndex(MemoContract.MemoEntry.COLUMN_TITLE));
                String content = cursor.getString(cursor.getColumnIndex(MemoContract.MemoEntry.COLUMN_CONTENT));
                String date = cursor.getString(cursor.getColumnIndex(MemoContract.MemoEntry.COLUMN_DATE));

                memos.add(new Memo(id, title, content, date));
            } while (cursor.moveToNext());
        }

        memoAdapter.notifyDataSetChanged();

        cursor.close();
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == 1) {
            if (resultCode == RESULT_OK) {
                loadMemos();
            }
        }
    }
}

9. 在 res/menu 文件夹中创建一个名为 main.xml 的新菜单文件，并添加以下代码：

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/deleteAll"
        android:title="Delete All" />
</menu>

10. 在 MainActivity.java 中添加以下代码：

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.deleteAll:
            getContentResolver().delete(MemoContract.MemoEntry.CONTENT_URI, null, null);
            loadMemos();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

11. 在 res/layout 文件夹中创建一个名为 activity_add_memo.xml 的新布局文件，并添加以下代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/titleEditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Title"
        android:textSize="20sp"
        android:textStyle="bold" />

    <EditText
        android:id="@+id/contentEditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:hint="Content"
        android:textSize="16sp" />

    <Button
        android:id="@+id/saveButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Save" />

</LinearLayout>

12. 在 AddMemoActivity.java 中添加以下代码：

public class AddMemoActivity extends AppCompatActivity {

    private EditText titleEditText, contentEditText;
    private Button saveButton;

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

        titleEditText = findViewById(R.id.titleEditText);
        contentEditText = findViewById(R.id.contentEditText);
        saveButton = findViewById(R.id.saveButton);

        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ContentValues values = new ContentValues();
                values.put(MemoContract.MemoEntry.COLUMN_TITLE, titleEditText.getText().toString());
                values.put(MemoContract.MemoEntry.COLUMN_CONTENT, contentEditText.getText().toString());
                values.put(MemoContract.MemoEntry.COLUMN_DATE, new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));

                getContentResolver().insert(MemoContract.MemoEntry.CONTENT_URI, values);

                setResult(RESULT_OK);
                finish();
            }
        });
    }
}

13. 在 MemoContract.java 中添加以下代码：

public class MemoContract {

    private MemoContract() {}

    public static final String CONTENT_AUTHORITY = "com.example.mymemoapp";
    public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);
    public static final String PATH_MEMOS = "memos";

    public static final class MemoEntry implements BaseColumns {
        public static final Uri CONTENT_URI = Uri.withAppendedPath(BASE_CONTENT_URI, PATH_MEMOS);

        public static final String TABLE_NAME = "memos";
        public static final String COLUMN_TITLE = "title";
        public static final String COLUMN_CONTENT = "content";
        public static final String COLUMN_DATE = "date";
    }
}

14. 在 MemoDbHelper.java 中添加以下代码：

public class MemoDbHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "memo.db";
    public static final int DATABASE_VERSION = 1;

    public MemoDbHelper(@Nullable Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        final String SQL_CREATE_MEMO_TABLE = "CREATE TABLE " +
                MemoContract.MemoEntry.TABLE_NAME + " (" +
                MemoContract.MemoEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                MemoContract.MemoEntry.COLUMN_TITLE + " TEXT NOT NULL, " +
                MemoContract.MemoEntry.COLUMN_CONTENT + " TEXT NOT NULL, " +
                MemoContract.MemoEntry.COLUMN_DATE + " TEXT NOT NULL" +
                ");";

        db.execSQL(SQL_CREATE_MEMO_TABLE);
    }

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

15. 在 AndroidManifest.xml 中添加以下代码：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

<provider
    android:name=".data.MemoProvider"
    android:authorities="com.example.mymemoapp"
    android:exported="false" />

<activity
    android:name=".AddMemoActivity"
    android:parentActivityName=".MainActivity" />

16. 在 MemoProvider.java 中添加以下代码：

public class MemoProvider extends ContentProvider {

    public static final int MEMOS = 100;
    public static final int MEMO_WITH_ID = 101;

    private MemoDbHelper dbHelper;

    private static final UriMatcher sUriMatcher = buildUriMatcher();

    private static UriMatcher buildUriMatcher() {
        UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

        uriMatcher.addURI(MemoContract.CONTENT_AUTHORITY, MemoContract.PATH_MEMOS, MEMOS);
        uriMatcher.addURI(MemoContract.CONTENT_AUTHORITY, MemoContract.PATH_MEMOS + "/#", MEMO_WITH_ID);

        return uriMatcher;
    }

    @Override
    public boolean onCreate() {
        dbHelper = new MemoDbHelper(getContext());
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection,
                        @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();

        int match = sUriMatcher.match(uri);

        Cursor cursor;

        switch (match) {
            case MEMOS:
                cursor = db.query(MemoContract.MemoEntry.TABLE_NAME, projection, selection, selectionArgs,
                        null, null, sortOrder);
                break;
            case MEMO_WITH_ID:
                selection = MemoContract.MemoEntry._ID + "=?";
                selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };

                cursor = db.query(MemoContract.MemoEntry.TABLE_NAME, projection, selection, selectionArgs,
                        null, null, sortOrder);
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        cursor.setNotificationUri(getContext().getContentResolver(), uri);

        return cursor;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        int match = sUriMatcher.match(uri);

        Uri returnUri;

        switch (match) {
            case MEMOS:
                long id = db.insert(MemoContract.MemoEntry.TABLE_NAME, null, values);
                if (id > 0) {
                    returnUri = ContentUris.withAppendedId(MemoContract.MemoEntry.CONTENT_URI, id);
                } else {
                    throw new SQLException("Failed to insert row into " + uri);
                }
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        getContext().getContentResolver().notifyChange(uri, null);

        return returnUri;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        int match = sUriMatcher.match(uri);

        int rowsDeleted;

        switch (match) {
            case MEMOS:
                rowsDeleted = db.delete(MemoContract.MemoEntry.TABLE_NAME, selection, selectionArgs);
                break;
            case MEMO_WITH_ID:
                selection = MemoContract.MemoEntry._ID + "=?";
                selectionArgs = new String[] { String.valueOf(ContentUris.parseId(uri)) };

                rowsDeleted = db.delete(MemoContract.MemoEntry.TABLE_NAME, selection, selectionArgs);
                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        if (rowsDeleted != 0) {
            getContext().getContentResolver().notifyChange(uri, null);
        }

        return rowsDeleted;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection,
                      @Nullable String[] selectionArgs) {
        throw new UnsupportedOperationException("Not yet implemented");
    }
}

这样，就完成了一个简单的 Android Studio 设计备忘录的增删改查功能的代码。