如何找出内容提供者是否包含数据？

Question

所以基本上，我有这个内容提供商，我用它来存储和检索数据库中的一些数据。在我的一个活动中，我有一个向这个数据库添加数据的功能;但是，我不希望那里有重复的条目。我的函数看起来是这样的：

public void addData(String data) { 
    if (/* data is not already in database */) { 
    ConstantValues values = new ConstantValues(); 
    values.put(DATA_FIELD, data); 
    getContentResolver().insert(CONTENT_URI, values); 
    } else { 
    // do nothing, it's already there 
    } 
} 

现在，我的问题是，我怎么能检查是否将数据由内容提供商已经存储？

编辑：

这是我的内容提供商的代码：

DataProvider.java

package org.frxstrem.xend; 
import java.util.HashMap; 
import org.frxstrem.xend.Data.Commands; 
import org.frxstrem.xend.Data.SerialNumbers; 
import android.content.ContentProvider; 
import android.content.ContentUris; 
import android.content.ContentValues; 
import android.content.Context; 
import android.content.UriMatcher; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.database.sqlite.SQLiteQueryBuilder; 
import android.net.Uri; 
import android.text.TextUtils; 
public class DataProvider extends ContentProvider { 

    private static final String DB_NAME = "xsend"; 
    private static final int DB_VERSION = 1; 

    private static final String TABLE_SN = "serial_numbers"; 
    private static final String TABLE_CMD = "commands"; 

    private static final int SN = 1; 
    private static final int SN_ID = 2; 
    private static final int CMD = 3; 
    private static final int CMD_ID = 4; 

    private static HashMap<String, String> snpm; 
    private static HashMap<String, String> cmdpm; 
    private static final UriMatcher uriMatcher; 

    private static class DatabaseHelper extends SQLiteOpenHelper { 

     public DatabaseHelper(Context c) { 
      super(c, DB_NAME, null, DB_VERSION); 
     } 
     @Override 
     public void onCreate(SQLiteDatabase db) { 
      db.execSQL("CREATE TABLE " + TABLE_SN + " (" 
        + SerialNumbers._ID + " INTEGER PRIMARY KEY, " 
        + SerialNumbers.TEXT + " TEXT" 
        + ");"); 
      db.execSQL("CREATE TABLE " + TABLE_CMD + " (" 
        + Commands._ID + " INTEGER PRIMARY KEY, " 
        + Commands.TEXT + " TEXT" 
        + ");"); 
     } 
     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      db.execSQL("DROP TABLE IF EXISTS " + TABLE_SN); 
      db.execSQL("DROP TABLE IF EXISTS " + TABLE_CMD); 
      onCreate(db); 
     } 

    } 

    private DatabaseHelper dbh; 

    @Override 
    public boolean onCreate() { 
     dbh = new DatabaseHelper(getContext()); 
     return true; 
    } 

    @Override 
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { 
     SQLiteQueryBuilder qb = new SQLiteQueryBuilder(); 
     String orderBy; 
     switch(uriMatcher.match(uri)) { 
     case SN: 
     { 
      qb.setTables(TABLE_SN); 
      qb.setProjectionMap(snpm); 
      orderBy = SerialNumbers.DEFAULT_SORT_ORDER; 
     } 
     break; 

     case SN_ID: 
     { 
      qb.setTables(TABLE_SN); 
      qb.setProjectionMap(snpm); 
      qb.appendWhere(SerialNumbers._ID + " = " + uri.getPathSegments().get(1)); 
      orderBy = SerialNumbers.DEFAULT_SORT_ORDER; 
     } 
     break; 
     case CMD: 
     { 
      qb.setTables(TABLE_CMD); 
      qb.setProjectionMap(cmdpm); 
      orderBy = Commands.DEFAULT_SORT_ORDER; 
     } 
     break; 

     case CMD_ID: 
     { 
      qb.setTables(TABLE_CMD); 
      qb.setProjectionMap(cmdpm); 
      qb.appendWhere(Commands._ID + " = " + uri.getPathSegments().get(1)); 
      orderBy = Commands.DEFAULT_SORT_ORDER; 
     } 
     break; 

     default: 
      throw new IllegalArgumentException("Unknown URI " + uri); 
     } 

     if(!TextUtils.isEmpty(sortOrder)) { 
      orderBy = sortOrder; 
     } 

     SQLiteDatabase db = dbh.getReadableDatabase(); 
     Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy); 

     c.setNotificationUri(getContext().getContentResolver(), uri); 
     return c; 
    } 

    @Override 
    public String getType(Uri uri) { 
     switch(uriMatcher.match(uri)) { 
     case SN: 
      return SerialNumbers.CONTENT_TYPE; 

     case SN_ID: 
      return SerialNumbers.CONTENT_ITEM_TYPE; 

     case CMD: 
      return Commands.CONTENT_TYPE; 

     case CMD_ID: 
      return Commands.CONTENT_ITEM_TYPE; 

     default: 
      throw new IllegalArgumentException("Unknown URI " + uri); 
     } 
    } 

    @Override 
    public Uri insert(Uri uri, ContentValues initialValues) { 
     Uri baseUri; 
     String table; 
     String nullColumnHack; 
     ContentValues values; 
     if(uriMatcher.match(uri) == SN) { 
      baseUri = SerialNumbers.CONTENT_URI; 
      table = TABLE_SN; 
      nullColumnHack = SerialNumbers.TEXT; 
      if(initialValues != null) 
       values = new ContentValues(initialValues); 
      else 
       values = new ContentValues(); 

      if(!values.containsKey(SerialNumbers.TEXT)) 
       throw new IllegalArgumentException("Text required"); 
     } else if(uriMatcher.match(uri) == CMD) { 
      baseUri = Commands.CONTENT_URI; 
      table = TABLE_CMD; 
      nullColumnHack = Commands.TEXT; 
      if(initialValues != null) 
       values = new ContentValues(initialValues); 
      else 
       values = new ContentValues(); 

      if(!values.containsKey(Commands.TEXT)) 
       throw new IllegalArgumentException("Text required"); 
     } else { 
      throw new IllegalArgumentException("Unknown URI " + uri); 
     } 

     SQLiteDatabase db = dbh.getWritableDatabase(); 
     long rowId = db.insert(table, nullColumnHack, values); 
     if(rowId > 0) { 
      Uri newUri = ContentUris.withAppendedId(baseUri, rowId); 
      getContext().getContentResolver().notifyChange(newUri, null); 
      return newUri; 
     } 

     throw new SQLException("Failed to insert row into " + uri); 
    } 

    @Override 
    public int delete(Uri uri, String where, String[] whereArgs) { 
     SQLiteDatabase db = dbh.getWritableDatabase(); 
     int count; 
     switch(uriMatcher.match(uri)) { 
     case SN: 
     { 
      count = db.delete(TABLE_SN, where, whereArgs); 
     } 
     break; 

     case SN_ID: 
     { 
      String msgId = uri.getPathSegments().get(1); 
      count = db.delete(TABLE_SN, SerialNumbers._ID + " = " + msgId + (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""), whereArgs); 
     } 
     break; 
     case CMD: 
     { 
      count = db.delete(TABLE_CMD, where, whereArgs); 
     } 
     break; 

     case CMD_ID: 
     { 
      String msgId = uri.getPathSegments().get(1); 
      count = db.delete(TABLE_CMD, Commands._ID + " = " + msgId + (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""), whereArgs); 
     } 
     break; 

     default: 
      throw new IllegalArgumentException("Unknown URI " + uri); 
     } 

     getContext().getContentResolver().notifyChange(uri, null); 
     return count; 
    } 

    @Override 
    public int update(Uri uri, ContentValues values, String where, String[] whereArgs) { 
     SQLiteDatabase db = dbh.getWritableDatabase(); 
     int count; 
     switch(uriMatcher.match(uri)) { 
     case SN: 
     { 
      count = db.update(TABLE_SN, values, where, whereArgs); 
     } 
     break; 

     case SN_ID: 
     { 
      String msgId = uri.getPathSegments().get(1); 
      count = db.update(TABLE_SN, values, SerialNumbers._ID + " = " + msgId + (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""), whereArgs); 
     } 
     break; 
     case CMD: 
     { 
      count = db.update(TABLE_CMD, values, where, whereArgs); 
     } 
     break; 

     case CMD_ID: 
     { 
      String msgId = uri.getPathSegments().get(1); 
      count = db.update(TABLE_CMD, values, Commands._ID + " = " + msgId + (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""), whereArgs); 
     } 
     break; 

     default: 
      throw new IllegalArgumentException("Unknown URI " + uri); 
     } 

     getContext().getContentResolver().notifyChange(uri, null); 
     return count; 
    } 

    static { 
     uriMatcher = new UriMatcher(UriMatcher.NO_MATCH); 
     uriMatcher.addURI(Data.AUTHORITY, "sn", SN); 
     uriMatcher.addURI(Data.AUTHORITY, "sn/#", SN_ID); 
     uriMatcher.addURI(Data.AUTHORITY, "cmd", CMD); 
     uriMatcher.addURI(Data.AUTHORITY, "cmd/#", CMD_ID); 

     snpm = new HashMap<String, String>(); 
     snpm.put(SerialNumbers._ID, SerialNumbers._ID); 
     snpm.put(SerialNumbers.TEXT, SerialNumbers.TEXT); 

     cmdpm = new HashMap<String, String>(); 
     cmdpm.put(Commands._ID, Commands._ID); 
     cmdpm.put(Commands.TEXT, Commands.TEXT); 
    } 
} 

Data.java

package org.frxstrem.xend; 
import android.net.Uri; 
import android.provider.BaseColumns; 
public class Data { 

    public static final String AUTHORITY = "org.frxstrem.xsend"; 

    private Data() { } 

    public static class SerialNumbers implements BaseColumns { 

     private SerialNumbers() { } 

     public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/sn"); 
     public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.frxstrem.serialnumber"; 
     public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.frxstrem.serialnumber"; 

     public static final String DEFAULT_SORT_ORDER = "_id ASC"; 

     public static final String TEXT = "text"; 

    } 

    public static class Commands implements BaseColumns { 

     private Commands() { } 
     public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/cmd"); 
     public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.frxstrem.command"; 
     public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.frxstrem.command"; 

     public static final String DEFAULT_SORT_ORDER = "_id ASC"; 

     public static final String TEXT = "text"; 

    } 
} 

Answer 1

我理解了它自己，使用下面的代码：

Cursor c = getContentResolver().query(CONTENT_URI, null, DATA_FIELD + " = " + DatabaseUtils.sqlEscapeString(data), null, null); 
if(c.getCount() == 0) { 
    // not found in database 
} 

Answer 2

查找内容提供者中数据的方法是使用ContentResolver.query（）。您要查询的内容取决于内容提供商，因此不知道很难说更多。