基本上，我有这个内容提供程序，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，我不希望有重复的条目。我的功能看起来像这样：
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，如何检查数据是否已由内容提供商存储？
修改
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";
}
}
答案 0 :(得分：10)
我自己想出来，使用以下代码：
Cursor c = getContentResolver().query(CONTENT_URI, null, DATA_FIELD + " = " + DatabaseUtils.sqlEscapeString(data), null, null);
if(c.getCount() == 0) {
// not found in database
}
答案 1 :(得分：1)
在ContentResolver.query（）中查找内容提供程序中的数据的方法。您将查询的具体内容取决于内容提供商，因此不知道很难说更多内容。