如何讀取數據庫到ArrayList？

Question

我是新來的Android Studio。我不知道如何讀取和添加數據庫到Arraylist。你能幫我一下嗎：P？我已經嘗試了一些方法，但它仍然沒有工作@。@。

 public class DatabaseHelper extends SQLiteOpenHelper 
{ 
      public static final String DATABASE_NAME = "ToDoList.db"; 
      public static final String TABLE_NAME = "ToDoList_Table"; 
      public static final String DATABASE_TABLE = "ToDo_DBTable"; 
      public static final String COL_1 = "ID"; 
      public static final String COL_2 = "TODO"; 

      public DatabaseHelper(Context context) { 
       super(context, DATABASE_NAME, null, 1); 
      } 

      @Override 
      public void onCreate(SQLiteDatabase db) { 
       db.execSQL("create table " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT,TODO TEXT)"); 
      } 

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

      public boolean insertData(String TODO) { 
       SQLiteDatabase db = this.getWritableDatabase(); 
       ContentValues contentValues = new ContentValues(); 
       contentValues.put(COL_2, TODO); 
       long result = db.insert(TABLE_NAME, null, contentValues); 
       if (result == -1) 
        return false; 
       else 
        return true; 
      } 
      public ArrayList<String> getRecords(){ 
       SQLiteDatabase db = this.getReadableDatabase(); 
       ArrayList<String> data=new ArrayList<String>(); 
       Cursor cursor = db.query(TABLE_NAME, new String[]{COL_2},null, null, null, null, null); 
       String fieldToAdd=null; 
       while(cursor.moveToNext()){ 
        fieldToAdd=cursor.getString(0); 
        data.add(fieldToAdd); 
       } 
       cursor.close(); 
       return data; 
      } 
     }  

    public class MainActivity extends AppCompatActivity 
    { 
     DatabaseHelper TDdb; 
     ArrayList<String> todoItems; 
     ArrayAdapter<String> aTodoAdapter; 
     ListView lvItems; 
     EditText editTD; 
     Button btnAddItems; 



     @Override 
     protected void onCreate(Bundle savedInstanceState) { 

      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_main); 
      android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar); 
      setSupportActionBar(toolbar); 
      populateArrayItems(); 

      editTD = (EditText) findViewById(R.id.tdEditText); 
      lvItems = (ListView) findViewById(R.id.lvItems); 
      btnAddItems = (Button) findViewById(R.id.tdAddItems); 
      AddData(); 

      getSupportActionBar().setDisplayShowHomeEnabled(true); 
      getSupportActionBar().setLogo(R.drawable.list_ingredients); 
      getSupportActionBar().setDisplayUseLogoEnabled(true); 
      lvItems.setAdapter(aTodoAdapter); 
      lvItems.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() { 
       @Override 
       public boolean onItemLongClick(AdapterView<?> parent, View view, int position, 
               long id) { 
        todoItems.remove(position); 
        aTodoAdapter.notifyDataSetChanged(); 
        return true; 
       } 
      }); 
      TDdb = new tdls.todolistapps.DatabaseHelper(this); 
     } 
     public void AddData() 
     { 
      btnAddItems.setOnClickListener(
        new View.OnClickListener() 
        { 
         @Override 
        public void onClick(View view) 
         { 
          boolean isInserted = TDdb.insertData(editTD.getText().toString()); 
          if(isInserted = true) 

           Toast.makeText(MainActivity.this,"Items Inserted",Toast.LENGTH_LONG).show(); 
           else 
           Toast.makeText(MainActivity.this,"Items not Inserted",Toast.LENGTH_LONG).show(); 

         } 
        } 
      ); 
     } 
     public void populateArrayItems() 
     { 
      todoItems = new ArrayList<String>(); 
      todoItems.add("Item 1"); 
      todoItems.add("Item 2"); 
      todoItems.add("Item 3"); 
      aTodoAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, todoItems); 

     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      // Inflate the menu; this adds items to the action bar if it is present. 
      getMenuInflater().inflate(R.menu.menu_main, menu); 
      menu.add("Email"); 
      return true; 
     } 


     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 
      // Handle action bar item clicks here. The action bar will 
      // automatically handle clicks on the Home/Up button, so long 
      // as you specify a parent activity in AndroidManifest.xml. 
      int id = item.getItemId(); 

      //noinspection SimplifiableIfStatement 
      if (id == R.id.action_settings) { 
       return true; 
      } 

      return super.onOptionsItemSelected(item); 
     } 

     public void onAddItem(View v) 
     { 
      aTodoAdapter.add(editTD.getText().toString()); 
      editTD.setText(""); 
     } 
    } 

下面是圖片，它表示項目插入，但它不會顯示：「（

Answer 1

嘗試更換下面的代碼

if(isInserted = true){ 
       todoItems.add(editTD.getText().toString()); 
       aTodoAdapter.notifyDataSetChanged(); 
       Toast.makeText(MainActivity.this,"Items Inserted",Toast.LENGTH_LONG).show(); 
} 
else { 
       Toast.makeText(MainActivity.this, "Items not Inserted", Toast.LENGTH_LONG).show(); 
} 

，因爲你需要更新適配器以及將數據添加到數據庫之後

Answer 2

At First cha您的getRecords（）函數如下：

public ArrayList<String> getRecords(){ 
    open(); 
    ArrayList<String> data = new ArrayList<>(); 
    Cursor cursor = db.query(DATABASE_TABLE, new String[]{COL_2}, null, null, null, null, null, null); 
    if (cursor.moveToFirst()){ 
     do { 
      data.add(cursor.getString(0)); 
     } while (cursor.moveToNext()); 
    } 
    close(); 
    return data; 
}