用android studio做一个日记app的实现代码

以下是一个简单的日记App的实现代码，使用了SQLite数据库存储数据：

1. activity_main.xml

<?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">

    <EditText
        android:id="@+id/titleEditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Title" />

    <EditText
        android:id="@+id/contentEditText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Content" />

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

    <ListView
        android:id="@+id/diaryListView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

</LinearLayout>

2. Diary.java

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

    public Diary(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;
    }
}

3. DiaryAdapter.java

public class DiaryAdapter extends BaseAdapter {
    private Context context;
    private List<Diary> diaryList;

    public DiaryAdapter(Context context, List<Diary> diaryList) {
        this.context = context;
        this.diaryList = diaryList;
    }

    @Override
    public int getCount() {
        return diaryList.size();
    }

    @Override
    public Object getItem(int position) {
        return diaryList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.diary_item_layout, parent, false);
        }

        TextView titleTextView = convertView.findViewById(R.id.titleTextView);
        TextView contentTextView = convertView.findViewById(R.id.contentTextView);
        TextView dateTextView = convertView.findViewById(R.id.dateTextView);

        Diary diary = diaryList.get(position);

        titleTextView.setText(diary.getTitle());
        contentTextView.setText(diary.getContent());
        dateTextView.setText(diary.getDate());

        return convertView;
    }
}

4. MainActivity.java

public class MainActivity extends AppCompatActivity {
    private EditText titleEditText, contentEditText;
    private Button saveButton;
    private ListView diaryListView;

    private List<Diary> diaryList;
    private DiaryAdapter diaryAdapter;

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

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

        diaryList = new ArrayList<>();
        diaryAdapter = new DiaryAdapter(this, diaryList);
        diaryListView.setAdapter(diaryAdapter);

        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String title = titleEditText.getText().toString().trim();
                String content = contentEditText.getText().toString().trim();

                if (TextUtils.isEmpty(title) || TextUtils.isEmpty(content)) {
                    Toast.makeText(MainActivity.this, "Title and content cannot be empty", Toast.LENGTH_SHORT).show();
                    return;
                }

                Diary diary = new Diary(0, title, content, new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.getDefault()).format(new Date()));
                DiaryDBHelper dbHelper = new DiaryDBHelper(MainActivity.this);
                SQLiteDatabase db = dbHelper.getWritableDatabase();

                ContentValues values = new ContentValues();
                values.put("title", diary.getTitle());
                values.put("content", diary.getContent());
                values.put("date", diary.getDate());

                db.insert("diary", null, values);

                diaryList.add(diary);
                diaryAdapter.notifyDataSetChanged();

                titleEditText.setText("");
                contentEditText.setText("");
            }
        });

        DiaryDBHelper dbHelper = new DiaryDBHelper(this);
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        Cursor cursor = db.query("diary", null, null, null, null, null, "id desc");
        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"));
                String date = cursor.getString(cursor.getColumnIndex("date"));

                Diary diary = new Diary(id, title, content, date);
                diaryList.add(diary);
            } while (cursor.moveToNext());
        }
        cursor.close();
        diaryAdapter.notifyDataSetChanged();
    }
}

5. DiaryDBHelper.java

public class DiaryDBHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "diary.db";
    private static final int DB_VERSION = 1;

    public DiaryDBHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

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

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

6. diary_item_layout.xml

<?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="10dp">

    <TextView
        android:id="@+id/titleTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="16sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/contentTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="14sp" />

    <TextView
        android:id="@+id/dateTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="12sp"
        android:textColor="@android:color/darker_gray" />

</LinearLayout>