_id即使我已经将它包含到create table语句中，该列也被认为不存在

Question

我想从数据库填充listview。当我尝试使用游标来做到这一点时，我得到一个错误：

android.database.sqlite.SQLiteException：no such column：_id（code 1）：，while compiling：SELECT _id FROM contacts WHERE _id ORDER BY name DESC

这里是我的代码：

MainActivity.java

package com.boggs.barr.barrboggscontactlist; 

import android.content.ContentValues; 
import android.content.Loader; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.net.Uri; 
import android.provider.ContactsContract; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.ListView; 
import android.widget.SimpleCursorAdapter; 

public class MainActivity extends AppCompatActivity { 

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

    } 
    public static final String KEY_ID = "_id"; 


    private void populateListView() { 

     String[] projection = { 
       KEY_ID 
     }; 

     FeedReaderDbHelper mDbHelper = new FeedReaderDbHelper(getApplicationContext()); 
     SQLiteDatabase db = mDbHelper.getWritableDatabase(); 

     String sortOrder = 
       FeedReaderContract.FeedEntry.COLUMN_NAME_NAME + " DESC"; 

     Cursor cursor = db.query(
       FeedReaderContract.FeedEntry.TABLE_NAME, // The table to query 
       projection,        // The columns to return 
       KEY_ID,        // The columns for the WHERE clause 
       null,       // The values for the WHERE clause 
       null,          // don't group the rows 
       null,          // don't filter by row groups 
       sortOrder         // The sort order 
     ); 
     String[] fromColumns = new String[] {FeedReaderContract.FeedEntry.COLUMN_NAME_NAME, FeedReaderContract.FeedEntry.COLUMN_NAME_PHONE}; 
     int[] toViews = {R.id.name, R.id.phone}; 

     SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, 
       R.layout.name_and_number, cursor, fromColumns, toViews, 0); 

     ListView listView = (ListView) findViewById(R.id.listView); 
     listView.setAdapter(adapter); 


} 

    @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); 
     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); 
    } 
} 

FeedReaderDbHelper.java

package com.boggs.barr.barrboggscontactlist; 

import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

import java.sql.RowId; 

/** 
* Created by adnroid developer site 
*/ 
public class FeedReaderDbHelper extends SQLiteOpenHelper { 
    // If you change the database schema, you must increment the database version. 
    public static final int DATABASE_VERSION = 1; 
    public static final String DATABASE_NAME = "FeedReader.db"; 
    public static final String LONG_TYPE = " Long"; 
    public static final String STRING_TYPE = " STRING"; 
    public static final String BYTE_TYPE = " BYTE"; 
    private static final String COMMA_SEP = ","; 
    private static final String SQL_CREATE_ENTRIES = 
      "CREATE TABLE " + FeedReaderContract.FeedEntry.TABLE_NAME + " (" + 
        FeedReaderContract.FeedEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + 
        FeedReaderContract.FeedEntry.COLUMN_NAME_PICTURE + STRING_TYPE + COMMA_SEP + 
        FeedReaderContract.FeedEntry.COLUMN_NAME_NAME + STRING_TYPE + COMMA_SEP + 
        FeedReaderContract.FeedEntry.COLUMN_NAME_EMAIL + STRING_TYPE + COMMA_SEP + 
        FeedReaderContract.FeedEntry.COLUMN_NAME_PHONE + STRING_TYPE + 
        ")"; 


    private static final String SQL_DELETE_ENTRIES = 
      "DROP TABLE IF EXISTS " + FeedReaderContract.FeedEntry.TABLE_NAME; 

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

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

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // This database is only a cache for online data, so its upgrade policy is 
     // to simply to discard the data and start over 
     db.execSQL(SQL_DELETE_ENTRIES); 
     onCreate(db); 
    } 
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     onUpgrade(db, oldVersion, newVersion); 
    } 
} 

FeedReaderContract.java

package com.boggs.barr.barrboggscontactlist; 

import android.provider.BaseColumns; 
import android.support.annotation.Nullable; 

/** 
* Created by android developer site. 
* attempted to do database ran out of time 
*/ 
public final class FeedReaderContract { 
    // To prevent someone from accidentally instantiating the contract class, 
    // give it an empty constructor. 
    public FeedReaderContract() {} 

    /* Inner class that defines the table contents */ 
    public static abstract class FeedEntry implements BaseColumns { 
     public static final String TABLE_NAME = "contacts"; 
     public static final String _ID = "_id"; 
     public static final String COLUMN_NAME_PICTURE = "picture"; 
     public static final String COLUMN_NAME_NAME = "name"; 
     public static final String COLUMN_NAME_EMAIL = "email"; 
     public static final String COLUMN_NAME_PHONE = "phone"; 
     public static final Nullable COLUMN_NAME_NULLABLE = null; 

    } 
} 

香港专业教育学院读，我需要ID传递给光标？但我不确定这意味着什么。对我来说，它应该工作，因为我将ID包含在要包含在光标中的列列表中。任何帮助表示赞赏！

编辑：我问这是因为有同样问题的人提出的解决方案不适合我。他们不断建议尝试使用RowId或.moveToFirst来包含ID。拉尔托被提出了一个适合我的解决方案。

Answer 1

正如用户laalto指出的那样，我需要从模拟器中卸载应用程序，因为我对模式进行了更改。一旦我这样做，该应用程序开始工作。