如何从sqllite表中获取数据

Question

嗨我写这个应用程序，需要使用数据库，我碰到了一个障碍。我似乎无法从数据库中获取信息。我有以下代码：

合同类：

public class SettingsContract { 
    private SettingsContract() { 

    } 

    public final class SettingsEntry implements BaseColumns { 
     public static final String TABLE_NAME = "Settings"; 
     public static final String COLUMN_NAME_LAST_REFRESH_DT = "LastRefreshDt"; 
    } 
} 

DbHelper类：

public class SettingsDbHelper extends SQLiteOpenHelper { 
    public static final int DATABASE_VERSION = 1; 
    public static final String DATABASE_NAME = "Database.db"; 

    private static final String SQL_CREATE_ENTRIES = 
     "CREATE TABLE IF NOT EXISTS" + SettingsContract.SettingsEntry.TABLE_NAME + " (" + 
       SettingsContract.SettingsEntry._ID + " INTEGER PRIMARY KEY," + 
       SettingsContract.SettingsEntry.COLUMN_NAME_LAST_REFRESH_DT + " DATE,"; 

    private static final String SQL_DELETE_ENTRIES = 
     "DROP TABLE IF EXISTS " + SettingsContract.SettingsEntry.TABLE_NAME; 

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

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     db.execSQL(SQL_CREATE_ENTRIES); 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     db.execSQL(SQL_DELETE_ENTRIES); 
     onCreate(db); 
    } 

    @Override 
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     onUpgrade(db, oldVersion, newVersion); 
    } 

} 

而且，我用这个代码：

private SettingsDbHelper dbHelper; 

    public SettingsDataSource(Context context) { 
     this.dbHelper = new SettingsDbHelper(context); 
    } 

    public Setting getSettings() { 
     SQLiteDatabase db = this.dbHelper.getReadableDatabase(); 
     Cursor cursor = db.rawQuery("SELECT " + 
SettingsContract.SettingsEntry.COLUMN_NAME_LAST_REFRESH_DT + " FROM " 
+ SettingsContract.SettingsEntry.TABLE_NAME, null); 
... 

现在，当我打电话rawQuery这是我在日志中的内容：

04-15 12:18:14.026 2698-2698/com.busridercluj E/SQLiteLog: 
(1) no such table: Settings 

我在这里错过了什么？为什么不按照它应该创建的表？

Answer 1

您创建的表查询是错误的，所以表没有被创建。

private static final String SQL_CREATE_ENTRIES = 
      "CREATE TABLE IF NOT EXISTS " + SettingsContract.SettingsEntry.TABLE_NAME + " (" + 
        SettingsContract.SettingsEntry._ID + " INTEGER PRIMARY KEY," + SettingsContract.SettingsEntry.COLUMN_NAME_LAST_REFRESH_DT + " DATE);"; 



@Override 
    public void onCreate(SQLiteDatabase db) { 
     Log.d("CreateDB", "Create table sql query: " + SQL_CREATE_ENTRIES); 
     db.execSQL(SQL_CREATE_ENTRIES); 
    } 

日志输出应为：CREATE TABLE IF NOT EXISTS Settings (_id INTEGER PRIMARY KEY, LastRefreshDt DATE);

Answer 2

这可能会帮助你...

MainActivity.class

public class MainActivity extends Activity { 

DatabaseClass dbclass; 
EditText et1,et2,et3; 
Button b1,b2; 

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

    et1 = (EditText) findViewById(R.id.editText1); 
    et2 = (EditText) findViewById(R.id.editText2); 
    et3 = (EditText) findViewById(R.id.editText3); 
    b1 = (Button) findViewById(R.id.button1); 
    b2 = (Button) findViewById(R.id.button2); 
    dbclass = new DatabaseClass(this); 
    onInsert(); 
    onShow(); 

} 

public void onInsert(){ 
    b1.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
          boolean isInserted = dbclass.InsertData(et1.getText().toString(), 
            et2.getText().toString(), 
            et3.getText().toString()); 

          if(isInserted ==true){ 
           Toast.makeText(getApplicationContext(), "data inserted", Toast.LENGTH_LONG).show(); 
          }else 
           Toast.makeText(getApplicationContext(), "data not inserted", Toast.LENGTH_LONG).show(); 

     } 
    }); 
} 

public void onShow(){ 
    b2.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      Intent in = new Intent(getApplicationContext(),ListActivity.class); 
      startActivity(in); 
      } 
    }); 
} 

}

助手类

public class DatabaseClass extends SQLiteOpenHelper{ 

public static final String DATABASE_NAME = "Student.db"; 
public static final String TABLE_NAME = "StudentData"; 
public static final String ID= "id"; 
public static final String NAME = "name"; 
public static final String SURNAME = "surname"; 
public static final String MARKS = "marks"; 

public DatabaseClass(Context context) { 
    super(context, TABLE_NAME, null, 1); 
    // TODO Auto-generated constructor stub 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL("CREATE TABLE "+TABLE_NAME+"(ID INTEGER PRIMARY KEY AUTOINCREMENT,NAME TEXT,SURNAME TEXT,MARKS INTEGER)"); 

} 

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

public boolean InsertData(String name,String surname,String marks){ 
    SQLiteDatabase db = this.getWritableDatabase(); 
    ContentValues cv = new ContentValues(); 
    cv.put("NAME", name); 
    cv.put("SURNAME", surname); 
    cv.put("MARKS", marks); 
    long result = db.insert(TABLE_NAME, null, cv); 
    if(result==-1){ 
     return false; 
    } 
    return true; 
} 

public Cursor getAllData(){ 
    SQLiteDatabase db = this.getWritableDatabase(); 
    Cursor res = db.rawQuery("SELECT * FROM TABLE NAME", null); 
    return res; 
} 

}

ListActivity.class

public class ListActivity extends Activity { 

ListView l; 
DatabaseClass dba; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.thelist); 
    dba = new DatabaseClass(this); 

    l = (ListView) findViewById(R.id.listView1); 
    ViewAll(); 



} 

public void ViewAll(){ 
    Cursor res = dba.getAllData(); 
    if(res.getCount()==0){ 
     Toast.makeText(this, "no data found", Toast.LENGTH_LONG).show(); 
     return; 
    } 

    /*StringBuffer buffer = new StringBuffer(); 
    while(res.moveToNext()){ 
     buffer.append("ID"+res.getString(0)+"\n"); 
     buffer.append("NAME"+res.getString(1)+"\n"); 
     buffer.append("SURNAME"+res.getString(2)+"\n"); 
     buffer.append("PRICE"+res.getString(3)+"\n"); 
    }*/ 
    //showmessage("DATA",buffer.toString());   
    ArrayAdapter<String> adap = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1,); 
    l.setAdapter(adap); 
} 

}

Adapter.class

public class MyAdapter extends ArrayAdapter<String> { 

private final Context context; 
private final String[] values; 

public MyAdapter(Context context,String[] values) { 
    super(context, R.layout.thelist, values); 
    this.context = context; 
    this.values = values; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    LayoutInflater inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE); 
    View row = inflater.inflate(R.layout.listitems, parent,false); 
    return super.getView(position, convertView, parent); 

    TextView tv1 = (TextView) row.findViewById(R.id.textname); 
    TextView tv2 = (TextView) row.findViewById(R.id.textsurname); 
    TextView tv3 = (TextView) row.findViewById(R.id.textmarks); 
} 

}