Android开发教程之ContentProvider数据存储
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一、ContentProvider保存数据介绍
一个程序可以通过实现一个ContentProvider的抽象接口将自己的数据完全暴露出去，而且ContentProvider是以类似数据库中表的方式将数据暴露的。那么外界获取其提供的数据，也就应该与从数据库中获取数据的操作基本一样，只不过是采用URL来表示外界需要访问的“数据库”。
ContentProvider提供了一种多应用间数据共享的方式。
ContentProvider是个实现了一组用于提供其他应用程序存取数据的标准方法的类。应用程序可以在ContentProvider中执行如下操作：查询数据、修改数据、添加数据、删除数据。
标准的ContentProvider：Android提供了一些已经在系统中实现的标准ContentProvider，比如联系人信息，图片库等等，可以用这些ContentProvider来访问设备上存储的联系人信息、图片等等。
在ContentProvider中使用的查询字符串有别于标准的SQL查询，很多诸如select、add、delete、modify等操作都使用一种特殊的URL进行，这种URL由3部分组成，“content://”，代表数据的路径和一个可选的表示数据的ID。
content://media/internal/images 这个URL将返回设备上存储的所有图片
content://contacts/people/ 这个URL将返回设备上的所有联系人信息
content://contacts/people/45 这个URL返回单个结果（联系人信息中ID为45的联系人记录）
如果想要存储字节型数据，比如位图文件等，那保存该数据的数据列其实是一个表示实际保存保存文件的URL字符串，客户端通过它来读取对应的文件数据，处理这种数据类型的ContentProvider需要实现一个名为_data的字段，_data字段列出了该文件在Android文件系统上的精确路径。这个字段不仅是供客户端使用，而且也可以供ContentResolver使用。客户端可以调用ContentResolver.openOutputStream()方法来处理该URL指向的文件资源，如果是ContentResolver本身的话，由于其持有的权限比客户端要高，所以它能直接访问该数据文件。
二、使用方法
大多数ContentProvider使用Android文件系统或者SQLite数据库来保持数据，但是也可以以任何方式来存储。本例用SQLite数据库来保持数据。
1.创建一个接口，定义了一个名为CONTENT_URL，并且是public static final的Uri类型的类变量，必须为其指定一个唯一的字符串值，最好的方案是类的全称，和数据列的名称。
public interface IProivderMetaData {
public static final String AUTHORITY = "com.zhangmiao.datastoragedemo";
public static final String DB_NAME = "book.db";
public static final int VERSION = 1;
public interface BookTableMetaData extends BaseColumns {
public static final String TABLE_NAME = "book";
public static final Uri CONTENT_URI = Uri.parse("content://"
+ AUTHORITY + "/" + TABLE_NAME);
public static final String BOOK_ID = "_id";
public static final String BOOK_NAME = "name";
public static final String BOOK_PUBLISHER = "publisher";
public static final String SORT_ORDER = "_id desc";
public static final String CONTENT_LIST = "vnd.android.cursor.dir/vnd.bookprovider.book";
public static final String CONTENT_ITEM = "vnd.android.cursor.item/vnd.bookprovider.book";
}
}2.实现SQLiteOpenHelper
public class ContentProviderDBHelper extends SQLiteOpenHelper implements IProivderMetaData {
private static final String TAG = "ContentProviderDBHelper";
public ContentProviderDBHelper(Context context) {
super(context, DB_NAME, null, VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
...
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
...
}
}3.创建一个继承了ContentProvider父类的类
public class ContentProviderDBHelper extends SQLiteOpenHelper implements IProivderMetaData {
public ContentProviderDBHelper(Context context) {
super(context, DB_NAME, null, VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
...
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
...
}
}4.在AndroidManifest.xml中使用标签来设置调用ContentProvider。
<provider
android:authorities="com.zhangmiao.datastoragedemo"
android:name=".BookContentProvider"/>5.增加数据
mContentResolver = getContentResolver();
String[] bookNames = new String[]{"Chinese", "Math", "English", "Sports"};
String[] bookPublishers = new String[]{"XinHua", "GongXin", "DianZi", "YouDian"};
for (int i = 0; i < bookNames.length; i++) {
ContentValues values = new ContentValues();
values.put(IProivderMetaData.BookTableMetaData.BOOK_NAME, bookNames[i]);
values.put(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER, bookPublishers[i]);
mContentResolver.insert(IProivderMetaData.BookTableMetaData.CONTENT_URI, values);
}6.删除数据
String bookId = "1";
if (!"".equals(bookId)) {
ContentValues values1 = new ContentValues();
values1.put(IProivderMetaData.BookTableMetaData.BOOK_ID,bookId);
mContentResolver.delete(Uri.withAppendedPath(
IProivderMetaData.BookTableMetaData.CONTENT_URI,
bookId),
"_id = ?",
new String[]{bookId}
);
} else {
mContentResolver.delete(
IProivderMetaData.BookTableMetaData.CONTENT_URI,
null,
null
);
}7.查询数据
Cursor cursor = mContentResolver.query(IProivderMetaData.BookTableMetaData.CONTENT_URI,
null, null, null, null);
String text = "";
if (cursor != null) {
while (cursor.moveToNext()) {
String bookIdText =
cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_ID));
String bookNameText =
cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_NAME));
String bookPublisherText =
cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER));
text += "id = " + bookIdText + ",name = " + bookNameText +
",publisher = " + bookPublisherText + "\n";
}
cursor.close();
mTableInfo.setText(text);
}8.更新数据
String bookId1 = "2";
String bookName = "Art";
String bookPublisher = "TieDao";
ContentValues values2 = new ContentValues();
values2.put(IProivderMetaData.BookTableMetaData.BOOK_NAME,bookName);
values2.put(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER,bookPublisher);
if ("".equals(bookId1)) {
mContentResolver.update(IProivderMetaData.BookTableMetaData.CONTENT_URI,
values2, null, null);
} else {
mContentResolver.update(Uri.withAppendedPath(IProivderMetaData.BookTableMetaData.CONTENT_URI, bookId1),
values2, "_id = ? ", new String[]{bookId1}
);
}三、小案例
1.添加strings.xml文件
<string name="content_provider">ContentProvider</string>
<string name="add_data">增加数据</string>
<string name="delete_data">删除数据</string>
<string name="update_data">更改数据</string>
<string name="query_data">查询数据</string>2.修改activity_main.xml文件
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.zhangmiao.datastoragedemo.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="@string/content_provider" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="@dimen/fab_margin"
android:layout_marginTop="@dimen/fab_margin"
android:orientation="horizontal">
<Button
android:id="@+id/provider_add"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="@string/add_data" />
<Button
android:id="@+id/provider_delete"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="@string/delete_data" />
<Button
android:id="@+id/provider_update"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="@string/update_data" />
<Button
android:id="@+id/provider_query"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="@string/query_data" />
</LinearLayout>
<TextView
android:id="@+id/table_info"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/app_name" />
</LinearLayout>
</android.support.design.widget.CoordinatorLayout>3.添加IProviderMetaData接口
package com.zhangmiao.datastoragedemo;
import android.net.Uri;
import android.provider.BaseColumns;
public interface IProviderMetaData {
public static final String AUTHORITY = "com.zhangmiao.datastoragedemo";
public static final String DB_NAME = "book.db";
public static final int VERSION = 1;
public interface BookTableMetaData extends BaseColumns {
public static final String TABLE_NAME = "book";
public static final Uri CONTENT_URI = Uri.parse("content://"
+ AUTHORITY + "/" + TABLE_NAME);
public static final String BOOK_ID = "_id";
public static final String BOOK_NAME = "name";
public static final String BOOK_PUBLISHER = "publisher";
public static final String SORT_ORDER = "_id desc";
public static final String CONTENT_LIST = "vnd.android.cursor.dir/vnd.bookprovider.book";
public static final String CONTENT_ITEM = "vnd.android.cursor.item/vnd.bookprovider.book";
}
}4.添加ContentProviderDBHelper类
package com.zhangmiao.datastoragedemo;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class ContentProviderDBHelper extends SQLiteOpenHelper implements IProviderMetaData {
private static final String TAG = "ContentProviderDBHelper";
public ContentProviderDBHelper(Context context) {
super(context, DB_NAME, null, VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String TABLESQL = "CREATE TABLE IF NOT EXISTS "
+ BookTableMetaData.TABLE_NAME + " ("
+ BookTableMetaData.BOOK_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
+ BookTableMetaData.BOOK_NAME + " VARCHAR,"
+ BookTableMetaData.BOOK_PUBLISHER + " VARCHAR)";
db.execSQL(TABLESQL);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion + "to"
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + DB_NAME);
onCreate(db);
}
}5.添加BookContentProvider类
package com.zhangmiao.datastoragedemo;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.annotation.Nullable;
import android.util.Log;
public class BookContentProvider extends ContentProvider {
private static final String TAG = "BookContentProvider";
private static UriMatcher uriMatcher = null;
private static final int BOOKS = 1;
private static final int BOOK = 2;
private ContentProviderDBHelper dbHelper;
private SQLiteDatabase db;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(IProviderMetaData.AUTHORITY,
IProviderMetaData.BookTableMetaData.TABLE_NAME, BOOKS);
uriMatcher.addURI(IProviderMetaData.AUTHORITY,
IProviderMetaData.BookTableMetaData.TABLE_NAME + "/#",
BOOK);
}
@Override
public boolean onCreate() {
dbHelper = new ContentProviderDBHelper(getContext());
return (dbHelper == null) ? false : true;
}
@Nullable
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {
case BOOKS:
return IProviderMetaData.BookTableMetaData.CONTENT_LIST;
case BOOK:
return IProviderMetaData.BookTableMetaData.CONTENT_ITEM;
default:
throw new IllegalArgumentException("This is a unKnow Uri"
+ uri.toString());
}
}
@Nullable
@Override
public Uri insert(Uri uri, ContentValues values) {
switch (uriMatcher.match(uri)) {
case BOOKS:
db = dbHelper.getWritableDatabase();
long rowId = db.insert(
IProviderMetaData.BookTableMetaData.TABLE_NAME,
IProviderMetaData.BookTableMetaData.BOOK_ID,
values);
Uri insertUri = Uri.withAppendedPath(uri, "/" + rowId);
Log.i(TAG, "insertUri:" + insertUri.toString());
getContext().getContentResolver().notifyChange(uri, null);
return insertUri;
case BOOK:
default:
throw new IllegalArgumentException("This is a unKnow Uri"
+ uri.toString());
}
}
@Nullable
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
db = dbHelper.getReadableDatabase();
switch (uriMatcher.match(uri)) {
case BOOKS:
return db.query(IProviderMetaData.BookTableMetaData.TABLE_NAME,
projection, selection, selectionArgs, null, null,
sortOrder);
case BOOK:
long id = ContentUris.parseId(uri);
String where = "_id=" + id;
if (selection != null && !"".equals(selection)) {
where = selection + " and " + where;
}
return db.query(IProviderMetaData.BookTableMetaData.TABLE_NAME,
projection, where, selectionArgs, null, null, sortOrder);
default:
throw new IllegalArgumentException("This is a unKnow Uri"
+ uri.toString());
}
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
db = dbHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case BOOKS:
return db.delete(IProviderMetaData.BookTableMetaData.TABLE_NAME,
selection, selectionArgs);
case BOOK:
long id = ContentUris.parseId(uri);
String where = "_id=" + id;
if (selection != null && !"".equals(selection)) {
where = selection + " and " + where;
}
return db.delete(IProviderMetaData.BookTableMetaData.TABLE_NAME,
selection, selectionArgs);
default:
throw new IllegalArgumentException("This is a unKnow Uri"
+ uri.toString());
}
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
db = dbHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case BOOKS:
return db.update(IProviderMetaData.BookTableMetaData.TABLE_NAME,
values, null, null);
case BOOK:
long id = ContentUris.parseId(uri);
String where = "_id=" + id;
if (selection != null && !"".equals(selection)) {
where = selection + " and " + where;
}
return db.update(IProviderMetaData.BookTableMetaData.TABLE_NAME,
values, selection, selectionArgs);
default:
throw new IllegalArgumentException("This is a unKnow Uri"
+ uri.toString());
}
}
}6.修改AndroidManifest.xml文件
<provider
android:authorities="com.zhangmiao.datastoragedemo"
android:name=".BookContentProvider"/>7.修改MainActivity
package com.zhangmiao.datastoragedemo;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.*;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {private ContentResolver mContentResolver;
private BookContentProvider mBookContentProvider;private TextView mTableInfo;
@Override
protected void onCreate(Bundle savedInstanceState) {
Log.v("MainActivity", "onCreate");
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button cpAdd = (Button) findViewById(R.id.provider_add);
Button cpDelete = (Button) findViewById(R.id.provider_delete);
Button cpUpdate = (Button) findViewById(R.id.provider_update);
Button cpQuery = (Button) findViewById(R.id.provider_query);
mTableInfo = (TextView) findViewById(R.id.table_info);
cpAdd.setOnClickListener(this);
cpDelete.setOnClickListener(this);
cpQuery.setOnClickListener(this);
cpUpdate.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {case R.id.provider_add:
mContentResolver = getContentResolver();
String[] bookNames = new String[]{"Chinese", "Math", "English", "Sports"};
String[] bookPublishers = new String[]{"XinHua", "GongXin", "DianZi", "YouDian"};
for (int i = 0; i < bookNames.length; i++) {
ContentValues values = new ContentValues();
values.put(IProviderMetaData.BookTableMetaData.BOOK_NAME, bookNames[i]);
values.put(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER, bookPublishers[i]);
mContentResolver.insert(IProviderMetaData.BookTableMetaData.CONTENT_URI, values);
}
break;
case R.id.provider_delete:
String bookId = "1";
if (!"".equals(bookId)) {
ContentValues values1 = new ContentValues();
values1.put(IProviderMetaData.BookTableMetaData.BOOK_ID,
bookId);
mContentResolver.delete(
Uri.withAppendedPath(
IProviderMetaData.BookTableMetaData.CONTENT_URI,
bookId
), "_id = ?",
new String[]{bookId}
);
} else {
mContentResolver.delete(
IProviderMetaData.BookTableMetaData.CONTENT_URI,
null,
null
);
}
break;
case R.id.provider_query:
Cursor cursor = mContentResolver.query(IProviderMetaData.BookTableMetaData.CONTENT_URI, null, null, null, null);
String text = "";
if (cursor != null) {
while (cursor.moveToNext()) {
String bookIdText =
cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_ID));
String bookNameText =
cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_NAME));
String bookPublisherText =
cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER));
text += "id = " + bookIdText + ",name = " + bookNameText + ",publisher = " + bookPublisherText + "\n";
}
cursor.close();
mTableInfo.setText(text);
}
break;
case R.id.provider_update:
String bookId1 = "2";
String bookName = "Art";
String bookPublisher = "TieDao";
ContentValues values2 = new ContentValues();
values2.put(IProviderMetaData.BookTableMetaData.BOOK_NAME,
bookName);
values2.put(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER,
bookPublisher);
if ("".equals(bookId1)) {
mContentResolver.update(
IProviderMetaData.BookTableMetaData.CONTENT_URI,
values2, null, null);
} else {
mContentResolver.update(
Uri.withAppendedPath(
IProviderMetaData.BookTableMetaData.CONTENT_URI, bookId1),
values2, "_id = ? ", new String[]{bookId1});
}
break;default:
Log.v("MainActivity", "default");
break;
}
}
}
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