ContentProvider（查询 插入 修改 删除 ）

注意 本篇实在sqlite的基础上编写的所以建议首先了解sqlite

首先建立两个模块

ContentProvider    ContentResolver

ContentProvider  里面需要建立表和建立连接 所以在这里需要建立DBHelp类

DBHelp代码如下所示

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

public class DBHelp extends SQLiteOpenHelper {
    public DBHelp(Context context) {
        super(context, "godv.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        //建表
        sqLiteDatabase.execSQL("create table godv(_id integer primary key autoincrement,name varchar)");
        //插入初始化数据
        sqLiteDatabase.execSQL("insert into godv (name) values ('godv')");
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

在ContentProvider下建立GodvProvider类继承ContentProvider代码：

import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;

/**
 * 操作Godv表的类
 */
public class GodvProvider extends ContentProvider {
    public GodvProvider() {
    }

    @Override
    public boolean onCreate() {
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] strings, String s, String[] strings1, String s1) {
        return null;
    }

    @Override
    public String getType(Uri uri) {
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues contentValues) {
        return null;
    }

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

    @Override
    public int update(Uri uri, ContentValues contentValues, String s, String[] strings) {
        return 0;
    }
}

注册provider   authorities全类名 小写 exported让别的应用可访问

写ContentProvider内部的实现

首先需要添加合法的URI

在GodvProvider里面定义静态变量 matcher  用来存放所有合法Uri容器

在static块中添加合法的uri

public class GodvProvider extends ContentProvider {

    //code如果没有匹配 返回的值 存放Uri的容器
    private static UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
    private DBHelp dbHelp;

    //保存一些合法的Uri
    //content://com.example.contentprovider.godvprovider(authority)/Godv(表名)
    //content://com.example.contentprovider.godvprovider(authority)/Godv(表名)/3(id)
    //参数一 在AndroidManifest.xml文件中定义的authority
    static {
        matcher.addURI("com.example.contentprovider.godvprovider", "/Godv", 1);
        //#匹配任意数字
        matcher.addURI("com.example.contentprovider.godvprovider", "/Godv/#", 2);
    }

    public GodvProvider() {
    }

    @Override
    public boolean onCreate() {
        dbHelp = new DBHelp(getContext());
        return false;
    }

---

查询 

补全GodvProvider写查询的代码 

 //content://com.example.contentprovider.godvprovider/Godv  不根据id操作
    //content://com.example.contentprovider.godvprovider/Godv/3 根据id操作
    @Override
    public Cursor query(Uri uri, String[] strings, String s, String[] strings1, String s1) {
        //根据不同uri查询   匹配Uri 返回对应code
        //得到sqlLiteDataBase
        SQLiteDatabase database = dbHelp.getReadableDatabase();
        Cursor cursor;
        int code = matcher.match(uri);
        if (code == 1) { //不根据id查询
            cursor = database.query("Godv", strings, s, strings1, s1, null, null, null);
        } else if (code == 2) {//根据id查询
            //得到id
            long id = ContentUris.parseId(uri);
            cursor = database.query("Godv", strings, "_id=?", new String[]{id + ""}, null, null, null);
        } else {
            throw new RuntimeException("查询的uri不合法");
        }

        return cursor;
    }

回到ContentResolver中写查询

    public void query(View view) {
        //得到ContentResolver 对象
        ContentResolver resolver = getContentResolver();
        //查询 得到cursor 根据id查询
        Uri uri = Uri.parse("content://com.example.contentprovider.godvprovider/Godv/1");
        //第二个参数 返回字段 null为全部 因为根据id查询所以后面参数一律为null
        Cursor cursor = resolver.query(uri, null, null, null, null, null);
        //取出数据显示
        if (cursor.moveToNext()) {
            String name = cursor.getString(1);
            int id = cursor.getInt(0);
            Toast.makeText(this, id + ":" + name, Toast.LENGTH_LONG).show();

        }
    }

查询完成

---

插入

补全GodvProvider写插入的代码 

 //插入没有根据id插入的
    @Override
    public Uri insert(Uri uri, ContentValues contentValues) {
        //得到连接
        SQLiteDatabase database = dbHelp.getReadableDatabase();
        //匹配uri
        int code = matcher.match(uri);
        //判断合法
        if (code == 1) {
            long id = database.insert("Godv", null, contentValues);
            //返回之前将id添加到uri当中
            uri = ContentUris.withAppendedId(uri, id);
            database.close();
            return uri;
        } else {
            database.close();
            throw new RuntimeException("插入的uri不合法");
        }
    }

回到ContentResolver中写插入

 public void insert(View view) {
        //得到ContentResolver 对象
        ContentResolver resolver = getContentResolver();
        //调用insert
        Uri uri = Uri.parse("content://com.example.contentprovider.godvprovider/Godv");
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", "jack");
        Uri insert = resolver.insert(uri, contentValues);
        Toast.makeText(this, insert.toString(), Toast.LENGTH_LONG).show();
    }

 插入完成

---

修改

补全GodvProvider写修改的代码 

    @Override
    public int update(Uri uri, ContentValues contentValues, String s, String[] strings) {
        //得到连接
        SQLiteDatabase database = dbHelp.getReadableDatabase();
        //匹配uri
        int code = matcher.match(uri);
        int upCount = -1;
        //判断合法
        if (code == 1) {
            //不根据id更新
            upCount = database.update("Godv", contentValues, s, strings);
            return upCount;
        } else if (code == 2) {
            long id = ContentUris.parseId(uri);
            upCount = database.update("Godv", contentValues, "_id=" + id, null);
        } else {
            database.close();
            throw new RuntimeException("更新的uri不合法");
        }
        database.close();
        return upCount;
    }

 回到ContentResolver中写修改

    public void update(View view) {
        //得到ContentResolver 对象
        ContentResolver resolver = getContentResolver();
        //更新
        Uri uri = Uri.parse("content://com.example.contentprovider.godvprovider/Godv/2");
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", "jack2");
        int updateCount = resolver.update(uri, contentValues, null, null);
        Toast.makeText(this, "updateCount=" + updateCount, Toast.LENGTH_LONG).show();
    }

修改完成

---

 删除

补全GodvProvider写删除的代码 

    @Override
    public int delete(Uri uri, String s, String[] strings) {
        //得到连接
        SQLiteDatabase database = dbHelp.getReadableDatabase();
        //匹配uri
        int code = matcher.match(uri);
        int delCount = -1;
        //判断合法
        if (code == 1) {
            //不根据id更新
            delCount = database.delete("Godv", s, strings);
            return delCount;
        } else if (code == 2) {
            long id = ContentUris.parseId(uri);
            delCount = database.delete("Godv", "_id=" + id, null);
        } else {
            database.close();
            throw new RuntimeException("删除的uri不合法");
        }
        database.close();
        return delCount;
    }

 回到ContentResolver中写删除

    public void delete(View view) {
        //得到ContentResolver 对象
        ContentResolver resolver = getContentResolver();
        //删除
        Uri uri = Uri.parse("content://com.example.contentprovider.godvprovider/Godv/2");
        int deleteCount = resolver.delete(uri, null, null);
        Toast.makeText(this, "deleteCount=" + deleteCount, Toast.LENGTH_LONG).show();
    }

删除完成 

---

本篇针对写代码的先后顺序进行代码展示