ContentProvider和数据库的创建和使用

contentprovider的创建主要是分享应用的数据库的数据，创建主要可分为4步：

1、创建数据库（注意即使创建了数据库类，只有在调用了sqLiteOpenHelper.getWritableDatabase()，数据库才会创建，而在清单文件里配置了provider，一开始就会加载，因此在provider的onCreate（）方法里调用这个函数创建数据库。

2、创建类继承contentProvider，在里面定义数据库的authority与后面mainfest里面的一致，代表content的主机名，相当于数据库地址，并且定义表的信息和uri的适配器，并添加uri到适配器中，当然这些静态常量也可以另外定义一个MetaData类来存储。

3、在mainfest 注册provider，主要包括contentProvder的name和authority属性，demo中都是定义为包名+contentprovider类。

4、在activity中利用getContentReceiver来得到contentReceiver对象操作数据库。

下面根据以上步骤展示下代码：

1、数据库构建

package com.example.user.mcontentproviderdemo;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * Created by user on 2016/10/17.
 */
public class MyDatabace extends SQLiteOpenHelper {
    final static String DATABACE_NAME ="MyFriends";
    final static int DATABACE_VISION =1;

    private String CREATE_FRIEND = "create table friends( _id integer primary key autoincrement, " +
            "name text not null, mobile text not null)";//

    public MyDatabace(Context context) {

        super(context, DATABACE_NAME, null, DATABACE_VISION);

    }

    @Override
    public void onCreate(SQLiteDatabase db)
    {

        db.execSQL(CREATE_FRIEND);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {

    }
}

　2 contentprovider类的构建：

package com.example.user.mcontentproviderdemo;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.provider.ContactsContract;
import android.support.annotation.Nullable;

import java.io.File;

/**
 * Created by user on 2016/10/18.
 */
public class MyContentProvider extends ContentProvider{
    //要共享的数据库
    private  static SQLiteOpenHelper sqLiteOpenHelper;

    public final  static  String AUTHORITY = "com.example.user.mcontentproviderdemo.MyContentProvider";

    //**********************为每个表定义变量信息，例子中就一个friend表***********************
    //*****************friends表**************************************//
    public final  static  String FRIENDS_TABLE ="friends";//表名
    //friends表的列明
    public final  static String FRIENDS_ID = "_id";
    public final  static String FRIENDS_NAME = "name";
    public final  static String FRIENDS_MOBILE = "mobile";
    public final static int  ALL_FRIENDS = 100; //当uri匹配是整个表格时候得返回值
    public  final  static  int ONE_FRIENDS = 1 ;//当uri匹配是整个表格的某一条目时候返回值
    public final static  String DEFAULT_SORT_ORDER = FRIENDS_ID+" desc";//定义默认排序

    //getType会用到的返回的类型
    private final  static  String ITEM_FRIENDS_TABLE_MIME = "vnd.android.cursor.item/vnd.com.example.user.mcontentproviderdemo.friends";
    private final  static  String ALL_FRIENDS_TABLE_MIME = "vnd.android.cursor.dir/vnd.com.example.user.mcontentproviderdemo.friends";



    private static final UriMatcher sUriMatcher;
    static {

        //初始化匹配器
        sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        //  为friends表添加匹配的uri，当匹配时返回后面的整数值
        sUriMatcher.addURI(AUTHORITY , File.separator+FRIENDS_TABLE , ALL_FRIENDS);
        sUriMatcher.addURI(AUTHORITY , File.separator+FRIENDS_TABLE+"/*",ONE_FRIENDS);

    }


    @Override
    public boolean onCreate() {
        sqLiteOpenHelper = new MyDatabace(getContext());
        SQLiteDatabase db = sqLiteOpenHelper.getWritableDatabase();
        db.close();
        return false;
    }

    @Nullable
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {

        Cursor cursor = null;
        SQLiteDatabase db=sqLiteOpenHelper.getWritableDatabase();
        cursor=db.query("friends", projection, selection, selectionArgs, null, null ,null );//DEFAULT_SORT_ORDER
        return cursor;
    }

    @Nullable
    @Override
    public String getType(Uri uri) {
        switch (sUriMatcher.match(uri))
        {
            case ALL_FRIENDS:
                return ALL_FRIENDS_TABLE_MIME;
            case ONE_FRIENDS:
                return ITEM_FRIENDS_TABLE_MIME;
            default:
                return "error";
        }

    }

    @Nullable
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        switch (sUriMatcher.match(uri))
        {
            case ALL_FRIENDS:
                System.out.println("匹配成功");
                SQLiteDatabase sqLiteDatabase = sqLiteOpenHelper.getWritableDatabase();
                sqLiteDatabase.insert("friends" , null ,values);
                sqLiteDatabase.close();

            default:
               break;

        }
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        return 0;
    }
}

　　3、配置文件中注册：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.user.mcontentproviderdemo">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <provider android:name="com.example.user.mcontentproviderdemo.MyContentProvider"
            android:authorities="com.example.user.mcontentproviderdemo.MyContentProvider"
            >
        </provider>

    </application>

</manifest>

　　4 在activity中使用：

package com.example.user.mcontentproviderdemo;

import android.content.ContentProvider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import java.net.URI;

public class MainActivity extends AppCompatActivity {

    Uri uri = Uri.parse("content://"+ MyContentProvider.AUTHORITY+"/"+MyContentProvider.FRIENDS_TABLE);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

//        ******************************插入*********************************
        ContentValues contentValues = new ContentValues();
        //id 在数据库是主键且自增长,所有可以不添加，当添加时候若数据库内是唯一的就会添加进数据库，若不是就不会插入此条
//        contentValues.put(MyContentProvider.FRIENDS_ID,111);
        contentValues.put(MyContentProvider.FRIENDS_NAME , "db");
        contentValues.put(MyContentProvider.FRIENDS_MOBILE , "1356076");
        Uri uri2 =getContentResolver().insert(uri,contentValues);
//        System.out.println(uri2.toString());

//        ******************************查询*********************************
        Cursor cursor = getContentResolver().query(uri , null , null , null ,null);//new String[]{"name"}
        //遍历cursor
        while(cursor.moveToNext())
        {
            Bundle bundle = cursor.getExtras();
            String name =  cursor.getString(cursor.getColumnIndex(MyContentProvider.FRIENDS_NAME));
            String mobile =  cursor.getString(cursor.getColumnIndex(MyContentProvider.FRIENDS_MOBILE));
            int id =  cursor.getInt(cursor.getColumnIndex(MyContentProvider.FRIENDS_ID ));
            System.out.println("id:"+id+"   name:" + name + "   mobile:"+mobile);
        }


    }
}