Android之ContentProvider(内容的提供者)与ContentResolver(内容访问者)

内容的提供者（ContentProvider）

1.作用：
    暴露本应用的私有数据，供其他应用使用。通过继承ContentProvider。

有选择地暴露插入、删除、修改和查询本应用数据的接口。

2.使用：
    继承ContentProvider抽象类，并选择性地增删改查方法

需要在清单文件中配置
authorities为包名
name为继承ContentProvider的那个类

 

<!--配置内容提供者-->
        <provider
            android:authorities="com.zking.administrator.g160618_android16_sqlite.LOGIN"
            android:name=".MyProvider"
            android:exported="true"
            ></provider>

内容访问者(ContentResolver)

1. 作用
访问内容提供者，并解析返回的数据

2. 使用
通过上下文对象获取内容解析者

ContentResolver resolver = this.getContentResolver();

下面举一个实例，只在调用，操作时打印结果。

新建一个Moudle：

新建一个db连接数据库的包DBHelper

    package com.zking.db;  
      
    import android.content.Context;  
    import android.database.sqlite.SQLiteDatabase;  
    import android.database.sqlite.SQLiteOpenHelper;  
    import android.util.Log;  
      
    /**  
     * Created by Administrator on 2017/6/27 0027.  
     */  
      
    public class DBHelper extends SQLiteOpenHelper {  
        /**  
         *  
         * @param context   上下文  
         * @param name       数据库名字(文件名)  
         * @param factory   数据库工厂  :null  
         * @param version    数据库版本  
         */  
        public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {  
            super(context, name, factory, version);  
            Log.i("test","构造方法");  
        }  
        //创建表  
        @Override  
        public void onCreate(SQLiteDatabase db) {  
            Log.i("test","创建表");  
            db.execSQL("create table login(uid integer primary key autoincrement,uname,upass)");  
        }  
        @Override  
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {  
            Log.i("test","升级");  
        }  
      
    //    @Override  
    //    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {  
    //        super.onDowngrade(db, oldVersion, newVersion);  
    //    }  
    }  

在activity_main.xml中这样写

    <?xml version="1.0" encoding="utf-8"?>  
    <LinearLayout  
        xmlns:android="http://schemas.android.com/apk/res/android"  
        xmlns:app="http://schemas.android.com/apk/res-auto"  
        xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"  
        android:layout_height="match_parent"  
        android:orientation="vertical"  
        tools:context="com.zking.administrator.g160618_android16_sqlite.MainActivity">  
      
        <EditText  
            android:layout_width="match_parent"  
            android:layout_height="wrap_content"  
            android:hint="用户名："  
            android:id="@+id/et_main_uname"  
            />  
        <EditText  
            android:layout_width="match_parent"  
            android:layout_height="wrap_content"  
            android:hint="密码："  
            android:id="@+id/et_main_upass"  
            />  
        <Button  
            android:layout_width="match_parent"  
            android:layout_height="wrap_content"  
            android:text="操作"  
            android:onClick="operation"  
            />  
      
      
    </LinearLayout>  

然后在与xml相对应的java代码中MainActivity添加数据到数据库中

    package com.zking.administrator.g160618_android16_sqlite;  
      
    import android.content.ContentValues;  
    import android.database.Cursor;  
    import android.database.sqlite.SQLiteDatabase;  
    import android.support.v7.app.AppCompatActivity;  
    import android.os.Bundle;  
    import android.util.Log;  
    import android.view.View;  
    import android.widget.EditText;  
    import android.widget.Toast;  
      
    import com.zking.db.DBHelper;  
      
    public class MainActivity extends AppCompatActivity {  
      
        private EditText et_main_uname;  
        private EditText et_main_upass;  
      
        @Override  
        protected void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.activity_main);  
            et_main_uname = (EditText) findViewById(R.id.et_main_uname);  
            et_main_upass = (EditText) findViewById(R.id.et_main_upass);  
        }  
        public void operation(View view){  
            String uname=et_main_uname.getText().toString();  
            String upass=et_main_upass.getText().toString();  
      
            DBHelper dbHelper=new DBHelper(this,"G160618.db",null,2);  
            SQLiteDatabase sqLiteDatabase=dbHelper.getWritableDatabase();  
            //添加1  
            for (int i = 0; i <100 ; i++) {  
                sqLiteDatabase.execSQL("insert into login(uname,upass) values('"+uname+i+"','"+upass+"')");  
            }  
            //添加2  
    //        ContentValues values=new ContentValues();  
    //        values.put("uname",uname);  
    //        values.put("upass",upass);  
    //        values.putNull("uid");  
    //        sqLiteDatabase.insert("login","uname",values);  
      
            //删除  
            //sqLiteDatabase.delete("login","uid=?",new String[]{102+""});  
      
            //修改  
    //        ContentValues values=new ContentValues();  
    //        values.put("uname",uname);  
    //        values.put("upass",upass);  
    //        sqLiteDatabase.update("login",values,"uid=?",new String[]{101+""});  
      
            //查询所有  
            int pageNo=2;    //第一页  
            int pageSize=5;  //每页5条  
            //minus  
    //        Cursor cursor=sqLiteDatabase.rawQuery("select * from login limit ?,?",new String[]{((pageNo-1)*pageSize)+"",pageSize+""});  
    //        while(cursor.moveToNext()){  
    //            int uid=cursor.getInt(cursor.getColumnIndex("uid"));  
    //            String name=cursor.getString(cursor.getColumnIndex("uname"));  
    //            String pass=cursor.getString(cursor.getColumnIndex("upass"));  
    //            Log.i("test",uid+" "+name+" "+pass);  
    //        }  
      
      
      
            Toast.makeText(this, "OK", Toast.LENGTH_SHORT).show();  
        }  
    }  

新建java MyProvider文件把内容提供出去

    package com.zking.administrator.g160618_android16_sqlite;  
      
    import android.content.ContentProvider;  
    import android.content.ContentValues;  
    import android.database.Cursor;  
    import android.database.sqlite.SQLiteDatabase;  
    import android.net.Uri;  
    import android.support.annotation.NonNull;  
    import android.support.annotation.Nullable;  
    import android.util.Log;  
      
    import com.zking.db.DBHelper;  
      
    /**  
     * Created by Administrator on 2017/7/17 0017.  
     */  
      
    public class MyProvider extends ContentProvider {  
        @Override  
        public boolean onCreate() {  
            Log.i("test","onCreate");  
            return false;  
        }  
      
        @Nullable  
        @Override  
        public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {  
            Log.i("test","query");  
      
            //把数据查询出来  
            DBHelper dbHelper=new DBHelper(getContext(),"G160618.db",null,2);  
            SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();  
            //sqLiteDatabase.rawQuery("select * from login",null);  
            return sqLiteDatabase.rawQuery("select * from login",null);  
        }  
      
        @Nullable  
        @Override  
        public String getType(@NonNull Uri uri) {  
            Log.i("test","getType");  
            return null;  
        }  
      
        @Nullable  
        @Override  
        public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {  
            Log.i("test","insert");  
            return null;  
        }  
      
        @Override  
        public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {  
            Log.i("test","delete");  
            return 0;  
        }  
      
        @Override  
        public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {  
            Log.i("test","update");  
            return 0;  
        }  
    }  

最后在xml里面对内容提供者进行配置，加上这样一句代码

 <!--配置内容提供者-->  
           <provider  
               android:authorities="com.zking.administrator.g160618_android16_sqlite.LOGIN"  
               android:name=".MyProvider"  
               android:exported="true"  
               ></provider>