内容提供者实现应用访问另一个应用的数据库

实现这么个需求：应用1创建数据库Account.db，应用2对Account.db进行操作

有两个办法。

首先记录第一个不合常理的方法：将创建的数据库的权限改为公开的可读可写的，然后其他应用就可以访问了。当然没人会这么做，太不安全还麻烦。在这里就不详细说了，之提供一个方法可以在代码里写shell命令：

public void myChmod() {

        try {
            String command = "chmod 777 /data/data/com.lgqrlchinese.createprdb/databases/Account.db ";//这里是shell命令，我修改数据库权限为777
            Runtime runtime = Runtime.getRuntime();
            runtime.exec(command);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

记录一下作为小白所学的方法。用到内容提供者ContentProvider：

新建一个类MyOpenHelper.java来创建数据库Account.db:

package com.lgqrlchinese.createprdb;

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

public class MyOpenHelper extends SQLiteOpenHelper {
    /**
     * context 上下文
     * name 数据库名字
     * factory 游标工厂
     * version  版本
     */
    public MyOpenHelper(Context context) {
        super(context, "Account.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20),phone varchar(20))");
        db.execSQL("insert into info(name,phone) values(?,?)", new String[]{"张三", "17865649855"});
        db.execSQL("insert into info(name,phone) values(?,?)", new String[]{"李四", "15364987564"});

    }

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

    }
}

首先实现在本应用中操作数据库，不妨直接查一查：MainActivity.java:

package com.lgqrlchinese.createprdb;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        MyOpenHelper myOpenHelper = new MyOpenHelper(getApplicationContext());
        SQLiteDatabase db = myOpenHelper.getReadableDatabase();
        Cursor cursor = db.query("info", null, null, null, null, null, null);
        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String name = cursor.getString(1);
                String phone = cursor.getString(2);
                System.out.println(name + phone);
            }
        }

    }

}

只是检验下数据库有木有问题，通过检测，没有问题，然后我们开始写内容提供者AccountContentProvider.java，其中有四个方法正好是对数据库的四个操作：增删改查。

package com.lgqrlchinese.createprdb;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

public class AccountContentProvider extends ContentProvider {
    //定义一个uriMathcher,路径匹配器
    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    private static final int QUERYSUCESS = 0;
    private static final int INSERTSUCESS = 0;
    private static final int UPDATESUCESS = 0;
    private static final int DELETESUCESS = 0;

    //静态代码块,添加匹配规则
    static {
        /**
         * authority 注意和清单文件里面配置的一样
         * path
         * code 一个常量
         */
        sURIMatcher.addURI("AccountContentProvider", "query", QUERYSUCESS);
        sURIMatcher.addURI("AccountContentProvider", "insert", INSERTSUCESS);
        sURIMatcher.addURI("AccountContentProvider", "update", UPDATESUCESS);
        sURIMatcher.addURI("AccountContentProvider", "delete", DELETESUCESS);

    }

    private MyOpenHelper myOpenHelper;

    public AccountContentProvider() {
    }

    @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.

        myOpenHelper = new MyOpenHelper(getContext());

        return false;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // Implement this to handle requests to delete one or more rows.
        int code = sURIMatcher.match(uri);
        if (code == DELETESUCESS) {
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            int delete = db.delete("info", selection, selectionArgs);
            return delete;
        } else {
            throw new IllegalArgumentException("delete您的路径不匹配，请检查路径");

        }
    }

    @Override
    public String getType(Uri uri) {
        // TODO: Implement this to handle requests for the MIME type of the data
        // at the given URI.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO: Implement this to handle requests to insert a new row.
        int code = sURIMatcher.match(uri);
        if (code == INSERTSUCESS) {
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            long insert = db.insert("info", null, values);
            Uri uri2 = Uri.parse("com.lgqrlchinese.insert" + insert);
            return uri2;
        } else {
            throw new IllegalArgumentException("insert您的路径不匹配，请检查路径");

        }
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        int code = sURIMatcher.match(uri);
        if (code == QUERYSUCESS) {
            //路径匹配成功，把query方法实现（数据库查询方法），造作数据库必须获得SQLiteDatabase对象
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            Cursor cursor = db.query("info", projection, selection, selectionArgs, null, null, sortOrder);
            //cursor不能关闭
            return cursor;


        } else {
            //路径不匹配
            throw new IllegalArgumentException("您的路径不匹配，请检查路径");
        }
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        // TODO: Implement this to handle requests to update one or more rows.
        int code = sURIMatcher.match(uri);
        if (code == UPDATESUCESS) {
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            int update = db.update("info", values, selection, selectionArgs);
            return update;
        } else {
            throw new IllegalArgumentException("update您的路径不匹配，请检查路径");

        }
    }
}

当然要在清单文件中配置内容提供者

        <provider
                android:name=".AccountContentProvider"
                android:authorities="AccountContentProvider"
                android:enabled="true"
                android:exported="true">
        </provider>

此时新建一个项目，开始第二个应用

在布局文件activity_main.xml中加入四个按钮分别是增删改查：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click1"
        android:text="add" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click2"
        android:text="delete" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click3"
        android:text="update" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click4"
        android:text="query" />

</LinearLayout>

在MainActivity.java中实现按钮的点击事件：

package com.lgqrlchinese.readdb;

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 android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    //add
    public void click1(View view) {
        Uri uri = Uri.parse("content://AccountContentProvider/insert");//路径和定义的路径一样
        ContentValues values = new ContentValues();
        /**
         * key 字段名
         * name 值
         */
        values.put("name", "赵六");
        values.put("phone", "15445896458");
        Uri insert = getContentResolver().insert(uri, values);
        System.out.println("insert:" + insert);


    }

    //delete
    public void click2(View view) {
        Uri uri = Uri.parse("content://AccountContentProvider/delete");//路径和定义的路径一样
        int delete = getContentResolver().delete(uri, "name=?", new String[]{"赵六"});
        Toast.makeText(getApplicationContext(), "删除了" + delete + "行", Toast.LENGTH_SHORT).show();


    }

    //update
    public void click3(View view) {
        Uri uri = Uri.parse("content://AccountContentProvider/update");//路径和定义的路径一样
        ContentValues values = new ContentValues();
        values.put("phone", 10086);
        int update = getContentResolver().update(uri, values, "name=?", new String[]{"张三"});
        Toast.makeText(getApplicationContext(), "更改了" + update + "行", Toast.LENGTH_SHORT).show();

    }

    //query
    public void click4(View view) {
        //拿到内容解析者，直接通过上下文拿取
        Uri uri = Uri.parse("content://AccountContentProvider/query");//路径和定义的路径一样
        Cursor cursor = getContentResolver().query(uri, null, null, null, null);
        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String name = cursor.getString(1);
                String phone = cursor.getString(2);
                System.out.println("应用二" + name + phone);

            }
        }
    }
}

这样就实现了第二个应用访问第一个应用的数据库。