Question

我目前正在制作记事本应用程序当我按一个按钮添加一个新音符时，它会转到添加活动的音符但是，当我点击完成时，注释本身不会更新到主页ListView ListView确实有一行项目，但行的标题不会出现可能是什么问题？

MainActivity.java

    public class MainActivity extends AppCompatActivity {

private Button button;
private ListView listview;
public static NoteAdapter adapter;
private ArrayList<Note> notesList;
private DatabaseHandler db;

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

    db = new DatabaseHandler(this);

    listview = (ListView) findViewById(R.id.listView);

    notesList = db.getAllNotes();
    adapter = new NoteAdapter(getApplicationContext(), notesList);

    button = (Button) findViewById(R.id.addButton);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(getApplicationContext(), NoteAddClass.class);
            startActivity(intent);
            adapter.notifyDataSetChanged();
        }
    });

    listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
            Note note = db.getNote(i);
            Intent intent = new Intent(getApplicationContext(), NoteViewClass.class);
            intent.putExtra("title", note.getTitle());
            intent.putExtra("message", note.getContent());

            startActivity(intent);
        }
    });


    listview.setAdapter(adapter);

    listview.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
        @Override
        public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l) {
            notesList.remove(i);
            adapter.notifyDataSetChanged();
            db.deleteNote(notesList.get(i));
            return false;
        }
    });
}
 }

NoteViewClass.java

    public class NoteViewClass extends AppCompatActivity {

private TextView title, message;

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

    title = (TextView) findViewById(R.id.titleViewTextView);
    message = (TextView) findViewById(R.id.messageViewTextView);

    Intent intent = getIntent();

    String title_intent = intent.getStringExtra("title");
    String message_intent = intent.getStringExtra("message");

    title.setText(title_intent);
    message.setText(message_intent);
}
}

NoteAddClass.java

    public class NoteAddClass extends AppCompatActivity {

private EditText title, message;
private Button button;

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

    title = (EditText) findViewById(R.id.titleEditText);
    message = (EditText) findViewById(R.id.messageEditText);
    button = (Button) findViewById(R.id.finishButton);

    DatabaseHandler db = new DatabaseHandler(this);

    db.addNote(new Note(title.getText().toString(), message.getText().toString()));

    MainActivity.adapter.notifyDataSetChanged();

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(getApplicationContext(), MainActivity.class);
            startActivity(intent);
        }
    });
}
}

NoteAdapter.java

    public class NoteAdapter extends ArrayAdapter<Note> {

public static class ViewHolder {
    TextView titleTextView;
}

public NoteAdapter(Context context, ArrayList<Note> list) {
    super(context, 0, list);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    Note note = getItem(position);

    ViewHolder viewHolder;

    if(convertView == null) {
        //save viewholder
        viewHolder = new ViewHolder();
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.list_row, parent, false);
        viewHolder.titleTextView = (TextView) convertView.findViewById(R.id.titleRowTextView);
        convertView.setTag(viewHolder);
    } else {
        viewHolder = (ViewHolder) convertView.getTag();
    }

    viewHolder.titleTextView.setText(note.getTitle());

    return convertView;
}
}

DatabaseHandler.java

    public class DatabaseHandler extends SQLiteOpenHelper {

// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "notesManager";

// Contacts table name
private static final String TABLE_OF_NOTES = "notes";

// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_TITLE = "title";
private static final String KEY_CONTENT = "content";

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

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    String CREATE_DATABASE_TABLE = "CREATE TABLE "
            + TABLE_OF_NOTES + "("
            + KEY_ID + " INTEGER PRIMARY KEY,"
            + KEY_TITLE + " TEXT,"
            + KEY_CONTENT + " TEXT" + ")";

    sqLiteDatabase.execSQL(CREATE_DATABASE_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLE_OF_NOTES);

    // Create tables again
    onCreate(sqLiteDatabase);
}

//!--------- Below to Handle CRUD Operations (Create, Read, Update, Delete)--------------!

public void addNote(Note note) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_TITLE, note.getTitle()); // Note Title
    values.put(KEY_CONTENT, note.getContent()); // Note Message

    // Inserting Row
    db.insert(TABLE_OF_NOTES, null, values);
    db.close(); // Closing database connection
}

//accepts a single id and returns the corresponding row item to this ID
public Note getNote(int id) {
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_OF_NOTES, new String[]
            { KEY_ID, KEY_TITLE, KEY_CONTENT }, KEY_ID + "=?",
            new String[] { String.valueOf(id) }, null, null, null, null);
    if (cursor != null)
        cursor.moveToFirst();

    //the first constructor, fetching the contents of the row
    Note note = new Note(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1), cursor.getString(2));
    // return contact
    return note;
}

//returns all notes in an arraylist format
public ArrayList<Note> getAllNotes() {
    ArrayList<Note> noteArrayList = new ArrayList<Note>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_OF_NOTES;

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Note note = new Note();
            note.setId(Integer.parseInt(cursor.getString(0)));
            note.setTitle(cursor.getString(1));
            note.setContent(cursor.getString(2));

            // Adding contact to list
            noteArrayList.add(note);
        } while (cursor.moveToNext());
    }

    // return contact list
    return noteArrayList;
}

//returns the total number of notes in the database
public int getNotesCount() {
    String countQuery = "SELECT  * FROM " + TABLE_OF_NOTES;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    cursor.close();

    // return count
    return cursor.getCount();
}

//updates a single note object i the database
public int updateNote(Note note) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_TITLE, note.getTitle());
    values.put(KEY_CONTENT, note.getContent());

    // updating row
    return db.update(TABLE_OF_NOTES, values, KEY_ID + " = ?",
            new String[] { String.valueOf(note.getId())});
}

//deleting a note
public void deleteNote(Note note) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_OF_NOTES, KEY_ID + " = ?",
            new String[] { String.valueOf(note.getId()) });
    db.close();
}
}

更新

它在这一行上给了我一个IndexOutOfBounds异常 db.deleteNote(notesList.get(i));

中的MainActivity.java中的setOnItemLongClickListener()

Answer 1

由于您从列表中删除了注释，然后使用相同的索引从列表中获取注释，因此您获得的索引超出范围

{{1}}

对于未显示的标题，您需要检查数据库以查看字符串是否存储，然后验证您是否将标题设置为Note类，然后getter方法返回该字符串，最后是适配器正在将该字符串加载到正确的视图中。

如果您想稍微不同，请查看使用CursorAdapter而不是ArrayAdapter。这样，您可以在更新数据库时将光标重新加载到适配器，而不是尝试同步这两者。

Answer 2

当您执行 db.addNote 或 db.deleteNote 时，适配器notesList不会更改。此方法更改数据库中的数据，但不更改 notesList = db.getAllNotes（）;

的适配器列表中的数据

做正确您必须在适配器中更改db更改列表之后。例如，将方法添加到适配器，如：

public void addToList(Note note){

  list.add(note);
  notifyDataSetChanged();

}

添加到db：

后使用它

Not note=new Note(title.getText().toString(), message.getText().toString());
db.addNote(note);
adapter.addToList(note);

添加了最新的备注（制作备注应用程序）时，ListView不会更新

2 个答案: