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;/** * Created by zhangmiao on 2016/12/20. */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;/** * Created by zhangmiao on 2016/12/20. */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;/** * Created by zhangmiao on 2016/12/21. */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; } }}