尝试从 OnItemLongClickListener 中访问 SQLite 数据库

Question

我正在尝试删除存储在 SQLite DB 中并显示在列表视图中的项目。

给我带来麻烦的操作在 OnItemLongClickListener() 中。错误

构造函数 DatabaseHandler(new AdapterView.OnItemLongClickListener(){}) 未定义

是与这一行的实例化DatabaseHandler db = new DatabaseHandler(this);

我认为问题出在 DatabaseHandler 的构造函数上，如何在 onItemLongClickListener() 中使用它？

MainActivity

public class MainActivity extends FragmentActivity implements OnClickListener {

ListView listView;
int lastIndex = -1;
ArrayList<Event> lstEvents = new ArrayList<Event>();

// detail view
TextView tvTitle, tvTime, tvDate;
ImageView ivPic;
View vw_master;

boolean _isBack = true;

ImageButton add;

String title;
String date;
String time;
int resId;

static final int PICK_CONTACT_REQUEST = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

    // // get detail controls
    tvTitle = (TextView) findViewById(R.id.textViewTitle);
    tvDate = (TextView) findViewById(R.id.textViewDate);
    tvTime = (TextView) findViewById(R.id.textViewTime);
    ivPic = (ImageView) findViewById(R.id.imageView1);

    add = (ImageButton) findViewById(R.id.add);
    add.setOnClickListener(this);

    // ///////////////////////////////LISTVIEW////////////////////////////////////////
    // Create the adapter to convert the array to views
    EventAdapter adapter = new EventAdapter(this, lstEvents);

    // attach adapter to a list view
    listView = (ListView) findViewById(R.id.listViewFragment);
    listView.setAdapter(adapter);



    listView.setOnItemLongClickListener(new OnItemLongClickListener() {

        @Override
        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                int arg2, long arg3) {

            // TODO Auto-generated method stub
            DatabaseHandler db = new DatabaseHandler(this);
            Event event = db.getEvent(arg2);
            List<Event> events = db.deleteEvent(event);

            return false;
        }

    });
    // ///////////////////////////////LISTVIEW////////////////////////////////////////

    // /////////////////////////////DATABASE/////////////////////////////////////////////
    DatabaseHandler db = new DatabaseHandler(this);
    // /////////////////////////////DATABASE/////////////////////////////////////////////

    List<Event> events = db.getAllContacts();

    adapter.addAll(events);
    adapter.notifyDataSetChanged();

}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    switch (v.getId()) {
    case R.id.add:
        Intent intent = new Intent(this, CreateActivity.class);
        startActivityForResult(intent, 100);
        break;
    }
}

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

    // /////////////////////////////DATABASE/////////////////////////////////////////////
    DatabaseHandler db = new DatabaseHandler(this);
    // /////////////////////////////DATABASE/////////////////////////////////////////////

    // Create the adapter to convert the array to views
    EventAdapter adapter = new EventAdapter(this, lstEvents);

    // attach adapter to a list view
    listView = (ListView) findViewById(R.id.listViewFragment);
    listView.setAdapter(adapter);

    if (requestCode == 100) {
        if (resultCode == RESULT_OK) {
            Bundle b = data.getExtras();
            title = b.getString("TITLE");
            time = b.getString("TIME");
            date = b.getString("DATE");

            Bitmap bitmap = b.getParcelable("BITMAP");


            /////CONVERTING A BITMAP TO A BYTE[]
            byte[] image = null;
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, bos);
            image = bos.toByteArray();
            /////////




            // /////////////////////////////DATABASE/////////////////////////////////////////////
            /**
             * CRUD OPERATIONS
             */

            Log.e("Insert: ", "Inserting ..");
            db.addEvent(new Event(0, title, time, date, image));

            // Reading all contacts
            Log.e("Reading: ", "Reading all contacts..");
            // List<Event> events = db.getAllContacts();
            List<Event> events = db.getAllContacts();
            adapter.addAll(events);
            adapter.notifyDataSetChanged();

            // logging all events

            for (Event ev : events) {
                String log = "Id: " + ev.get_Id() + " ,Title: "
                        + ev.get_title() + " ,Date: " + ev.get_date()
                        + " ,RESOURCEID: " + ev.get_image();
                // Writing Contacts to log
                Log.e("Name: ", log);

            }

            // /////////////////////////////DATABASE/////////////////////////////////////////////
        }

    }
}
}

数据库处理程序

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 = "scheduleManager";

// Contacts table name
private static final String TABLE_EVENTS = "events";


// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_TITLE = "title";
private static final String KEY_TIME = "time";
private static final String KEY_DATE = "date";
private static final String KEY_IMAGE = "image";

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

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub
    String CREATE_EVENTS_TABLE = "CREATE TABLE " + TABLE_EVENTS + "("
            + KEY_ID + " INTEGER," + KEY_TITLE + " TEXT,"
            + KEY_TIME + " TEXT," + KEY_DATE + " TEXT," + KEY_IMAGE + " BLOB" + ")";
    db.execSQL(CREATE_EVENTS_TABLE);

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_EVENTS);

    // Create tables again
    onCreate(db);

}

/**
 * All CRUD(Create, Read, Update, Delete) Operations
 */


//adding an event (NEEDS TO ADD DRAWABLE)
 public void addEvent(Event event) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_ID, event.get_Id()); //Event ID
        values.put(KEY_TITLE, event.get_title()); // Event Title
        values.put(KEY_TIME, event.get_time()); // Event Time
        values.put(KEY_DATE, event.get_date()); // Event Date
        values.put(KEY_IMAGE, event.get_image()); // Event RESOURCEID

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

   // Getting single contact
   public Event getEvent(int id) {
       SQLiteDatabase db = this.getReadableDatabase();

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

       Event event = new Event(Integer.parseInt(cursor.getString(0)),
               cursor.getString(1), cursor.getString(2), cursor.getString(3), cursor.getBlob(4));
       // return contact
       return event;
   }


    // Getting All Contacts
   public List<Event> getAllContacts() {
      List<Event> eventList = new ArrayList<Event>();
      // Select All Query
      String selectQuery = "SELECT  * FROM " + TABLE_EVENTS;

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

      // looping through all rows and adding to list
      if (cursor.moveToFirst()) {
          do {

              Event event = new Event();
              event.set_Id(Integer.parseInt(cursor.getString(0)));
              event.set_title(cursor.getString(1));
              event.set_time(cursor.getString(2));
              event.set_date(cursor.getString(3));                          
              event.set_image(cursor.getBlob(4));
              eventList.add(event);
          } while (cursor.moveToNext());
      }

      // return contact list
      return eventList;
  }

// Getting event Count
    public int getEventsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_EVENTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

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

 // Updating single contact
    public int updateEvent(Event event) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_TITLE, event.get_title());
        values.put(KEY_TIME, event.get_time());
        values.put(KEY_DATE, event.get_date());

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

    // Deleting single contact
    public void deleteEvent(Event event) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_EVENTS, KEY_ID + " = ?",
                new String[] { String.valueOf(event.get_Id()) });
        db.close();
    }

}

Answer 1

改变你的

DatabaseHandler db = new DatabaseHandler(this);

这个

DatabaseHandler db = new DatabaseHandler(getActivity());

数据库处理程序需要上下文，在listView.setOnItemLongClickListener内部使用时this与this类不同，因此在onClickListener内部使用时应使用getActivity()。

其他可能的解决方案，而不是getActivity()

1. MainActivity.this
2. MainActivity.getActivity()

Answer 2

记住任何 onclick 或 ontouch 或 onitemlongclick 等...类型的侦听器都有自己的上下文。对我来说，你可以定义一个全局变量 Context context 并且在你的 oncreate 中你可以将它初始化为 context=this （它应该在任何 onclick 或 onitemlongclick 等之外。它应该在 oncreate 的主要内容中）现在你可以使用这个上下文在 longclick ， Toast ， constructors....等的整个班级中......

此外，在执行任何数据库活动之前，您没有使用 db.open() 打开与 db 的连接... 谢谢

Answer 3

更改 -> DatabaseHandler db = new DatabaseHandler(this);

致DatabaseHandler db = new DatabaseHandler(MainActivity.this);