从我的SQLite数据库中删除一些东西

Question

我正在使用有关如何创建数据库和存储输入信息的教程，例如编辑文本的信息，它很有效。但我只是遇到一个问题。删除该数据的唯一方法是使用列表视图长按活动中的项目，然后单击“删除”我想要这样做，以便您可以在单击按钮上删除该项。我已经尝试过查看所有代码，但我无法弄清楚，对数据库不熟悉，什么不是。所以，如果你能帮助我，那就太好了。这是我认为做数据库工作的类。

我相信主要的一个：

import java.util.Arrays;
import java.util.HashSet;

import android.content.ContentProvider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;

import com.name.todo.database.TodoDatabaseHelper;
import com.name.todo.database.TodoTable;



public class MyTodoContentProvider extends ContentProvider {

  // database
  private TodoDatabaseHelper database;

  // used for the UriMacher
  private static final int TODOS = 10;
  private static final int TODO_ID = 20;

  private static final String AUTHORITY = "com.name.todo.contentprovider";

  private static final String BASE_PATH = "todos";
  public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
      + "/" + BASE_PATH);

  public static final String CONTENT_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE
      + "/todos";
  public static final String CONTENT_ITEM_TYPE = ContentResolver.CURSOR_ITEM_BASE_TYPE
      + "/todo";

  private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);
  static {
    sURIMatcher.addURI(AUTHORITY, BASE_PATH, TODOS);
    sURIMatcher.addURI(AUTHORITY, BASE_PATH + "/#", TODO_ID);
  }

  @Override
  public boolean onCreate() {
    database = new TodoDatabaseHelper(getContext());
    return false;
  }

  @Override
  public Cursor query(Uri uri, String[] projection, String selection,
      String[] selectionArgs, String sortOrder) {

    // Uisng SQLiteQueryBuilder instead of query() method
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    // check if the caller has requested a column which does not exists
    checkColumns(projection);

    // Set the table
    queryBuilder.setTables(TodoTable.TABLE_TODO);

    int uriType = sURIMatcher.match(uri);
    switch (uriType) {
    case TODOS:
      break;
    case TODO_ID:
      // adding the ID to the original query
      queryBuilder.appendWhere(TodoTable.COLUMN_ID + "="
          + uri.getLastPathSegment());
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }

    SQLiteDatabase db = database.getWritableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection,
        selectionArgs, null, null, sortOrder);
    // make sure that potential listeners are getting notified
    cursor.setNotificationUri(getContext().getContentResolver(), uri);

    return cursor;
  }

  @Override
  public String getType(Uri uri) {
    return null;
  }

  @Override
  public Uri insert(Uri uri, ContentValues values) {
    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsDeleted = 0;
    long id = 0;
    switch (uriType) {
    case TODOS:
      id = sqlDB.insert(TodoTable.TABLE_TODO, null, values);
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return Uri.parse(BASE_PATH + "/" + id);
  }

  @Override
  public int delete(Uri uri, String selection, String[] selectionArgs) {
    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsDeleted = 0;
    switch (uriType) {
    case TODOS:
      rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO, selection,
          selectionArgs);
      break;
    case TODO_ID:
      String id = uri.getLastPathSegment();
      if (TextUtils.isEmpty(selection)) {
        rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO,
            TodoTable.COLUMN_ID + "=" + id, 
            null);
      } else {
        rowsDeleted = sqlDB.delete(TodoTable.TABLE_TODO,
            TodoTable.COLUMN_ID + "=" + id 
            + " and " + selection,
            selectionArgs);
      }
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return rowsDeleted;
  }

  @Override
  public int update(Uri uri, ContentValues values, String selection,
      String[] selectionArgs) {

    int uriType = sURIMatcher.match(uri);
    SQLiteDatabase sqlDB = database.getWritableDatabase();
    int rowsUpdated = 0;
    switch (uriType) {
    case TODOS:
      rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
          values, 
          selection,
          selectionArgs);
      break;
    case TODO_ID:
      String id = uri.getLastPathSegment();
      if (TextUtils.isEmpty(selection)) {
        rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
            values,
            TodoTable.COLUMN_ID + "=" + id, 
            null);
      } else {
        rowsUpdated = sqlDB.update(TodoTable.TABLE_TODO, 
            values,
            TodoTable.COLUMN_ID + "=" + id 
            + " and " 
            + selection,
            selectionArgs);
      }
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    getContext().getContentResolver().notifyChange(uri, null);
    return rowsUpdated;
  }

  private void checkColumns(String[] projection) {
    String[] available = { TodoTable.COLUMN_CATEGORY,
        TodoTable.COLUMN_SUMMARY, TodoTable.COLUMN_DESCRIPTION,
        TodoTable.COLUMN_ID };
    if (projection != null) {
      HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
      HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(available));
      // check if all columns which are requested are available
      if (!availableColumns.containsAll(requestedColumns)) {
        throw new IllegalArgumentException("Unknown columns in projection");
      }
    }
  }

} 

import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

public class TodoTable {

  // Database table
  public static final String TABLE_TODO = "todo";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_CATEGORY = "category";
  public static final String COLUMN_SUMMARY = "summary";
  public static final String COLUMN_DESCRIPTION = "description";

  // Database creation SQL statement
  private static final String DATABASE_CREATE = "create table " 
      + TABLE_TODO
      + "(" 
      + COLUMN_ID + " integer primary key autoincrement, " 
      + COLUMN_CATEGORY + " text not null, " 
      + COLUMN_SUMMARY + " text not null," 
      + COLUMN_DESCRIPTION
      + " text not null" 
      + ");";

  public static void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

  public static void onUpgrade(SQLiteDatabase database, int oldVersion,
      int newVersion) {
    Log.w(TodoTable.class.getName(), "Upgrading database from version "
        + oldVersion + " to " + newVersion
        + ", which will destroy all old data");
    database.execSQL("DROP TABLE IF EXISTS " + TABLE_TODO);
    onCreate(database);
  }
} 

另一个

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

public class TodoDatabaseHelper extends SQLiteOpenHelper {

  private static final String DATABASE_NAME = "todotable.db";
  private static final int DATABASE_VERSION = 1;

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

  // Method is called during creation of the database
  @Override
  public void onCreate(SQLiteDatabase database) {
    TodoTable.onCreate(database);
  }

  // Method is called during an upgrade of the database,
  // e.g. if you increase the database version
  @Override
  public void onUpgrade(SQLiteDatabase database, int oldVersion,
      int newVersion) {
    TodoTable.onUpgrade(database, oldVersion, newVersion);
  }
}