008_02_ContentProvider

什么是ContentProvider(内容提供者)?

 

ContentProvider维护特定的应用数据，并可以让其它应用轻松访问该数据。对数据使用者来说它是数据提供者。它提供统一的接口对数据进行操作，使用者不用关心数据到底是如何存储的以及数据类型到底是什么。也就是说，Content Provider作为数据提供者，提供了对外共享私有数据一种机制，使Android应用能方便地基于该机制进行数据访问。

 

开发ContentProvider步骤：

1，定义自己的ContentProvider类，该类需要继承Android提供的ContentProvider类；

2，向Android系统注册这个“网站”，也就是在AndroidManifest.xml文件中注册这个ContentProvider,就像注册Activity一样。注册这个ContentProvider时需要为它绑定一个Uri。

　　authorities属性就相当于该网站的域名。

         <provider
              android:name="com.example.myprovider.MyContentProvider"
              android:authorities="com.example.mycontentprovider"
              android:exported="true">
        </provider>

 URL与Uri比较

程序源代码

package com.example.mydbopenhelper;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.text.AlteredCharSequence;
import android.util.Log;

public class MydbOpenHelper extends SQLiteOpenHelper {
    public MydbOpenHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String createtable = "create table userphonenum(id int, name varchar(20), telephone char(11));";
        db.execSQL(createtable);  
        ContentValues c = new ContentValues();
        //id int ,name string ,password string
        for(int i=1;i<5;i++){
            c.put("id", i);
            c.put("name", "user"+i);
            c.put("telephone", "1371111111"+i);     
            db.insert("userphonenum", null, c);
        }
        System.out.println("MydbOpenHelper.onCreate()");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    
        String createtable = "create table userwechat(id int, name varchar(20), wechat char(11));";
        db.execSQL(createtable);
        ContentValues c = new ContentValues();
        //id int ,name string ,password string
        for(int i=1;i<5;i++){
            c.put("id", i);
            c.put("name", "user"+i);
            c.put("wechat", "weixin00"+i);
            db.insert("userwechat", null, c);
        }
        System.out.println("MydbOpenHelper.onCreate()");    
        Log.i("MydbOpenHelper", "oldervserion"+oldVersion+"newversion"+newVersion);
        System.out.println("MydbOpenHelper.onUpgrade()");
    }
}

package com.example.myprovider;

import java.util.List;

import com.example.mydbopenhelper.MydbOpenHelper;

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;

public class MyContentProvider extends ContentProvider{
    SQLiteDatabase db;
    static UriMatcher um = new UriMatcher(UriMatcher.NO_MATCH);
    static{
        um.addURI("com.example.mycontentprovider", "userphonenum", 1);
        um.addURI("com.example.mycontentprovider", "userwechat", 2);
        um.addURI("com.example.mycontentprovider", "userwechat/#", 3);
        um.addURI("com.example.mycontentprovider", "userwechat/*", 4);
        um.addURI("com.example.mycontentprovider", "userwechat/*/#", 5);
    }
    @Override
    public boolean onCreate() {
        MydbOpenHelper helper = new MydbOpenHelper(getContext(), "userinfo.db", null, 2);
        db = helper.getReadableDatabase();
        return false;
    }
    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        Cursor c = null;
        if(um.match(uri) == 1){
            c = db.query("userphoneum", projection, selection, selectionArgs, null, null, null);
        }
        else if(um.match(uri)==2){}
        else if(um.match(uri)==3){
            long l = ContentUris.parseId(uri);
            c = db.query("userphonenum", projection, selection, selectionArgs, null, null, null);
        }
        else if(um.match(uri) ==4){
            List<String> l = uri.getPathSegments();
            String agr = l.get(1);    
            c = db.query("userwechat",new String[] {agr}, null, null, null, null, null);
        }
        return c;
    }

    @Override
    public String getType(Uri uri) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        //判断用户需要插入的到底是哪个数据库
        if(um.match(uri)==1){
            db.insert("userphonenum", null, values);
        }
        else if(um.match(uri) == 2){
            db.insert("userwechat", null, values);
        }
        return null;
    }

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

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

}

package com.example.day08_contentprovider;

import com.example.mydbopenhelper.MydbOpenHelper;

import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        MydbOpenHelper helper = new MydbOpenHelper(this, "userinfo.db", null, 2);
        SQLiteDatabase db = helper.getReadableDatabase();
    }
}