android 玩转ContentProvider之一－－实现ContentProvider操作数据库

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本文详细介绍了ContentProvider在Android开发中的用法，包括其核心组件、数据库操作类、常量定义、数据操作类以及Activity测试实现。通过实例演示了如何创建、查询、更新和删除数据库中的数据。

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我的理解：ConetntRolver(用户使用入口)---------->ContentProvider(提供统一操作数据库的入口)-------->SqlIteHelper操作数据库

本人原创作品，谢绝转载！

作为android四大组件之一，今天总结一下它的用法。

ContentProvider官方有很多地方提到，其中一个是在API文档上（http://developer.android.com/guide/topics/providers/content-providers.html）面有介绍，有兴趣去看一下，虽然是英文的，对了解ContentProvider很有用；还有一个地方是android SDK中的%android_home%/samples/android-x/下面的一个NotePad的demo，代码架构可以参考该demo。本文来自此demo，并做相关修改。

代码：

SQLite数据库直接操作类：

[java] view plain copy

DatabaseHelper.java

[java] view plain copy

package com.jacp.database;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import com.jacp.demo.provider.Provider;
/**
* 操作数据库
* @author jacp
*
*/
public class DatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "jacp_demo.db";
private static final int DATABASE_VERSION = 1;
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + Provider.PersonColumns.TABLE_NAME + " ("
+ Provider.PersonColumns._ID + " INTEGER PRIMARY KEY,"
+ Provider.PersonColumns.NAME + " TEXT,"
+ Provider.PersonColumns.AGE + " INTEGER"
+ ");");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + Provider.PersonColumns.TABLE_NAME);
onCreate(db);
}
}

保存跟数据库及表有关的常量：
Provider.java

[java] view plain copy

package com.jacp.demo.provider;
import android.net.Uri;
import android.provider.BaseColumns;
/**
* 存放跟数据库有关的常量
* @author jacp
*
*/
public class Provider {
// 这个是每个Provider的标识，在Manifest中使用
public static final String AUTHORITY = "com.jacp.provider.demo.person";
public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.jacp.demo";
public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.jacp.demo";
/**
* 跟Person表相关的常量
* @author jacp
*
*/
public static final class PersonColumns implements BaseColumns {
// CONTENT_URI跟数据库的表关联，最后根据CONTENT_URI来查询对应的表
public static final Uri CONTENT_URI = Uri.parse("content://"+ AUTHORITY +"/persons");
public static final String TABLE_NAME = "person";
public static final String DEFAULT_SORT_ORDER = "age desc";
public static final String NAME = "name";
public static final String AGE = "age";
}
}

对数据增删改查操作的类：

PersonProvider.java

[java] view plain copy

package com.jacp.demo.provider;
import java.util.HashMap;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;
import com.jacp.database.DatabaseHelper;
/**
* 操作数据库Person表的ContentProvider
* @author jacp
*
*/
public class PersonProvider extends ContentProvider {
private static HashMap<String, String> sPersonsProjectionMap;
private static final int PERSONS = 1;
private static final int PERSONS_ID = 2;
private static final UriMatcher sUriMatcher;
private DatabaseHelper mOpenHelper;
@Override
public boolean onCreate() {
mOpenHelper = new DatabaseHelper(getContext());
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
String sortOrder) {
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
qb.setTables(Provider.PersonColumns.TABLE_NAME);
switch (sUriMatcher.match(uri)) {
case PERSONS:
qb.setProjectionMap(sPersonsProjectionMap);
break;
case PERSONS_ID:
qb.setProjectionMap(sPersonsProjectionMap);
qb.appendWhere(Provider.PersonColumns._ID + "=" + uri.getPathSegments().get(1));
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
// If no sort order is specified use the default
String orderBy;
if (TextUtils.isEmpty(sortOrder)) {
orderBy = Provider.PersonColumns.DEFAULT_SORT_ORDER;
} else {
orderBy = sortOrder;
}
// Get the database and run the query
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);
// Tell the cursor what uri to watch, so it knows when its source data changes
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
@Override
public String getType(Uri uri) {
switch (sUriMatcher.match(uri)) {
case PERSONS:
return Provider.CONTENT_TYPE;
case PERSONS_ID:
return Provider.CONTENT_ITEM_TYPE;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
}
@Override
public Uri insert(Uri uri, ContentValues initialValues) {
// Validate the requested uri
if (sUriMatcher.match(uri) != PERSONS) {
throw new IllegalArgumentException("Unknown URI " + uri);
}
ContentValues values;
if (initialValues != null) {
values = new ContentValues(initialValues);
} else {
values = new ContentValues();
}
// Make sure that the fields are all set
if (values.containsKey(Provider.PersonColumns.NAME) == false) {
values.put(Provider.PersonColumns.NAME, "");
}
if (values.containsKey(Provider.PersonColumns.AGE) == false) {
values.put(Provider.PersonColumns.AGE, 0);
}
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
long rowId = db.insert(Provider.PersonColumns.TABLE_NAME, Provider.PersonColumns.NAME, values);
if (rowId > 0) {
Uri noteUri = ContentUris.withAppendedId(Provider.PersonColumns.CONTENT_URI, rowId);
getContext().getContentResolver().notifyChange(noteUri, null);
return noteUri;
}
throw new SQLException("Failed to insert row into " + uri);
}
@Override
public int delete(Uri uri, String where, String[] whereArgs) {
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)) {
case PERSONS:
count = db.delete(Provider.PersonColumns.TABLE_NAME, where, whereArgs);
break;
case PERSONS_ID:
String noteId = uri.getPathSegments().get(1);
count = db.delete(Provider.PersonColumns.TABLE_NAME, Provider.PersonColumns._ID + "=" + noteId
+ (!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 = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)) {
case PERSONS:
count = db.update(Provider.PersonColumns.TABLE_NAME, values, where, whereArgs);
break;
case PERSONS_ID:
String noteId = uri.getPathSegments().get(1);
count = db.update(Provider.PersonColumns.TABLE_NAME, values, Provider.PersonColumns._ID + "=" + noteId
+ (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""), whereArgs);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
static {
sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
// 这个地方的persons要和PersonColumns.CONTENT_URI中最后面的一个Segment一致
sUriMatcher.addURI(Provider.AUTHORITY, "persons", PERSONS);
sUriMatcher.addURI(Provider.AUTHORITY, "persons/#", PERSONS_ID);
sPersonsProjectionMap = new HashMap<String, String>();
sPersonsProjectionMap.put(Provider.PersonColumns._ID, Provider.PersonColumns._ID);
sPersonsProjectionMap.put(Provider.PersonColumns.NAME, Provider.PersonColumns.NAME);
sPersonsProjectionMap.put(Provider.PersonColumns.AGE, Provider.PersonColumns.AGE);
}
}

表对应的数据对象：
Person.java

[java] view plain copy

package com.jacp.pojos;
public class Person {
public String name;
public int age;
}

Activity测试：
ContentProviderDemoActivity.java

[java] view plain copy

package com.jacp.demo;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import com.jacp.demo.provider.Provider;
import com.jacp.pojos.Person;
public class ContentProviderDemoActivity extends Activity {
private static final String TAG = "ProviderActivity";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
test();
}
private void test() {
Person p = new Person();
p.name = "jacp";
p.age = 99;
int id = insert(p);
query(id);
}
private int insert(Person person) {
ContentValues values = new ContentValues();
values.put(Provider.PersonColumns.NAME, person.name);
values.put(Provider.PersonColumns.AGE, person.age);
Uri uri = getContentResolver().insert(Provider.PersonColumns.CONTENT_URI, values);
Log.i(TAG, "insert uri="+uri);
String lastPath = uri.getLastPathSegment();
if (TextUtils.isEmpty(lastPath)) {
Log.i(TAG, "insert failure!");
} else {
Log.i(TAG, "insert success! the id is " + lastPath);
}
return Integer.parseInt(lastPath);
}
private void query(int id) {
Cursor c = getContentResolver().query(Provider.PersonColumns.CONTENT_URI, new String[] { Provider.PersonColumns.NAME, Provider.PersonColumns.AGE }, Provider.PersonColumns._ID + "=?", new String[] { id + "" }, null);
if (c != null && c.moveToFirst()) {
Person p = new Person();
p.name = c.getString(c.getColumnIndexOrThrow(Provider.PersonColumns.NAME));
p.age = c.getInt(c.getColumnIndexOrThrow(Provider.PersonColumns.AGE));
Log.i(TAG, "person.name="+p.name+"---person.age="+p.age);
} else {
Log.i(TAG, "query failure!");
}
}
}