Android开发教程之ContentProvider数据存储

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。

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

  ContentProvider
  增加数据
  删除数据
  更改数据
  查询数据

2.修改activity_main.xml文件

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

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;
    }
  }
}