ContentProvider_

作者：木道寻08 | 2024-08-17 14:52:05

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一、什么是ContentProvider？
      ContentProvider是一个抽象类，可以理解为一个特殊的存储数据的类型，它提供了一套标准的接口来获取和操作数据。可以把数据封装到ContentProvider 中，从而是这些数据可以被其他的应用程序所共享。搭建起了所有应用程序之间数据交换的桥梁！

二、ContentProvider的创建过程
1.创建一个类继承ContentProvider
继承它需要实现其所有的抽象方法
a.onCreate() ：初始化该ContentProvider
b.query(Uri,String[],String,Sring[],String) :通过Uri进行查询，返回Uri
c.intert(Uri,ContentValues):将数据插入到Uri所指定的位置
d.update(Uri,ContentValues,String,String []):更新uri指定位置的数据
e.delete(Uri,String,String[]):删除uri指定位置的数据
f.getType(Uri):返回数据的类型

2.声明CONTENT_URI，实现UriMatcher
每个ContentProvider都会对外提供一个公共的Uri，当有数据共享的时候，就需要使用ContentProvider为这些数据定义一个Uri，
UriMatcher是一个用来匹配Uri的工具类
public static final String AUTHORITY="com.example.provider.students";
private static final UriMatcher Urimatcher;
Urimatcher=new UriMatcher(UriMatcher.NO_MATCH);
//添加需要匹配的Uri，匹配则返回相应的匹配码
Urimatcher.addURI(Students.AUTHORITY, "student", STUDENT);
Urimatcher.addURI(Students.AUTHORITY, "student/#", STUDENT_ID);

3.在AndroidManifest.xml中注册
<provider
            android:name=".StudentContentProvider"
            android:authorities="com.example.provider.students"
            />
三、ContentProvider的使用实例
1.常量类，声明需要使用的常量

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package com.example.provider;
import android.net.Uri;
import android.provider.BaseColumns;
/**
*
* @author zt
*常量类，声明要使用的常量
*内部类Student实现了BaseColumns接口，该接口也是一个常量接口
该常量接口中已经定义了_id和_count常量，分别用来表示记录的id和已经记录的数量
*/
public finalclass Students{
//定义常量
public staticfinalString AUTHORITY="com.example.provider.students";
private Students(){}
//内部类
public staticfinalclass Studentimplements BaseColumns{
private Student(){}//构造方法
public staticfinalUri CONTENT_URI=Uri.parse("content://"+AUTHORITY+"/student");
public staticfinalString CONTENT_TYPE="vnd.android.cursor.dir/vnd.example.provider.students";
public staticfinalString CONTENT_ITEM_TYPE="vnd.android.cursor.item/vnd.example.provider.students";
//数据库中的表字段
public staticfinalString NMAE="name";//姓名
public staticfinalString GENDER="gender";//性别
public staticfinalString AGE="age";//年龄
}
}

2.利用数据库帮助类SQLiteOpenHelper来创建数据库

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package com.example.provider;
import com.example.provider.Students.Student;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DbHelperextends SQLiteOpenHelper{
//数据库的名称
private staticfinalString DATABASE_NAME="student.db";
private staticfinalint DATABASE_VERSION=1;
public staticfinalString TABLE_NAME="student";
public DbHelper(Contextcontext){
super(context, DATABASE_NAME,null, DATABASE_VERSION);
}
/**
* 创建table
*/
@Override
public void onCreate(SQLiteDatabase db){
//创建学生信息表，包括四个字段
//包括id、姓名、性别、年龄
String sql="create table "+TABLE_NAME+" ("
+Student._ID+" integer primary key,"
+Student.NMAE+" text,"
+Student.GENDER+" text,"
+Student.AGE+" integer "+");";
db.execSQL(sql);
}
/**
* 更新表
*/
@Override
public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){
String sql="drop table if exits student";
db.execSQL(sql);
}
}

3.创建StudentContentProvider类继承ContentProvider

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package com.example.provider;
import java.util.HashMap;
import com.example.provider.Students.Student;
import android.content.ContentProvider;
import android.content.ContentResolver;
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;
import android.text.TextUtils;
public class StudentContentProviderextends ContentProvider{
//声明数据库帮助类对象
private DbHelper dbHelper;
//定义ContentResolver 对象
private ContentResolver resolver;
//定义Uri工具类
private staticfinal UriMatcher Urimatcher;
//匹配码
private staticfinalint STUDENT=1;
private staticfinalint STUDENT_ID=2;
//需要查询的列集合
private staticHashMap<String,String> stu;
//
static
{
Urimatcher=new UriMatcher(UriMatcher.NO_MATCH);
//添加需要匹配的Uri，匹配则返回相应的匹配码
Urimatcher.addURI(Students.AUTHORITY,"student", STUDENT);
Urimatcher.addURI(Students.AUTHORITY,"student/#", STUDENT_ID);
//实例化集合
stu=newHashMap<String,String>();
//添加查询列map
stu.put(Student._ID, Student._ID);
stu.put(Student.NMAE,Student.NMAE);
stu.put(Student.GENDER, Student.GENDER);
stu.put(Student.AGE,Student.AGE);
}
/**
* 初始化
*/
@Override
public boolean onCreate(){
//创建DbHelper对象
dbHelper=new DbHelper(getContext());
return true;
}
/**
* 查询数据
*/
@Override
public Cursorquery(Uriuri,String[] projection,String selection,
String[] selectionArgs,String sortOrder){
SQLiteDatabase db=dbHelper.getReadableDatabase();
Cursor cursor;
switch(Urimatcher.match(uri))
{
case STUDENT:
cursor=db.query(DbHelper.TABLE_NAME,projection, selection,
selectionArgs, null, null, sortOrder);
break;
case STUDENT_ID:
String stuId=uri.getPathSegments().get(1);
String where="Student._ID="+stuId;
if(selection!=null&&"".equals(selection.trim()))//trim()函数的功能是去掉首尾空格
{
where+=" and "+selection;
}
cursor=db.query(DbHelper.TABLE_NAME, projection, where, selectionArgs,null,null, sortOrder);
break;
default:
//如果传进来的Uri不是我们需要的类型
throw new IllegalArgumentException("this is Unknown Uri："+uri);
}
return cursor;
}
/**
* 获得类型
*/
@Override
public StringgetType(Uriuri){
return null;
}
/**
* 插入数据
*/
@Override
public Uriinsert(Uriuri, ContentValuesvalues){
//获得可写入的数据库
SQLiteDatabase db=dbHelper.getWritableDatabase();
ContentResolver resolver=this.getContext().getContentResolver();
//插入数据，返回行号ID
long rowid=db.insert(DbHelper.TABLE_NAME, Student.NMAE, values);
//如果插入成功，返回Uri
if(rowid>0)
{
Uri stuUri=ContentUris.withAppendedId(uri, rowid);
resolver.notifyChange(stuUri,null);//数据发送变化时候，发出通知给注册了相应uri的
return stuUri;
}
return null;
}
/**
* 删除数据
*/
@Override
public intdelete(Uriuri,String selection,String[] selectionArgs){
SQLiteDatabase db=dbHelper.getWritableDatabase();
resolver=this.getContext().getContentResolver();
int count;
//根据返回的匹配码进行相应的删除动作
switch(Urimatcher.match(uri))
{
case STUDENT:
count=db.delete(DbHelper.TABLE_NAME, selection, selectionArgs);
break;
case STUDENT_ID://只删除对于的id
//getPathSegments()方法得到一个String的List
String stuId=uri.getPathSegments().get(1);
count=db.delete(DbHelper.TABLE_NAME, Student._ID+"="+stuId+(!TextUtils.isEmpty(selection)?
" and ("+selection+')':""), selectionArgs);
break;
default:
//如果传进来的Uri不是我们需要的类型
throw new IllegalArgumentException("this is Unknown Uri："+uri);
}
resolver.notifyChange(uri,null);
return count;
}
/**
* 更新数据
*/
@Override
public intupdate(Uriuri, ContentValuesvalues,String selection,
String[] selectionArgs){
SQLiteDatabase db=dbHelper.getWritableDatabase();//创建一个可读的数据库
resolver=this.getContext().getContentResolver();
int count;
switch(Urimatcher.match(uri))
{
case STUDENT:
count=db.update(DbHelper.TABLE_NAME,values, selection, selectionArgs);
break;
case STUDENT_ID:
String stuId=uri.getPathSegments().get(1);//获得id
count=db.update(DbHelper.TABLE_NAME,values,Student._ID+"="+stuId+(!TextUtils.isEmpty(selection)?
" and ("+selection+')':""), selectionArgs);
break;
default:
//如果传进来的Uri不是我们需要的类型
throw new IllegalArgumentException("this is Unknown Uri："+uri);
}
resolver.notifyChange(uri,null);
return count;
}
}

4.创建一个Activity 来测试，查询、删减、插入、更新数据

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package com.example.provider;
import com.example.provider.Students.Student;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
public class MyContentProviderextendsActivity{
private staticfinalString TAG="MyContentProvider";
private ContentResolver resolver;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
insert();//插入数据
// delete(1);//删除第一行
update(4);
query();//查询
}
//插入数据
public voidinsert()
{
Uri uri=Student.CONTENT_URI;
//获得ContentResolver对象
resolver=this.getContentResolver();
ContentValues values=new ContentValues();
//添加学生信息
values.put(Student.NMAE,"Jack");
values.put(Student.GENDER,"男");
values.put(Student.AGE, 20);
//将信息插入
resolver.insert(uri,values);
Log.i(TAG,uri.toString());
}
//删除数据
//删除第id行
public voiddelete(Integerid)
{
//指定uri
Uri uri=ContentUris.withAppendedId(Student.CONTENT_URI,id);
resolver=this.getContentResolver();
resolver.delete(uri,null,null);
}
//更新
public voidupdate(Integerid)
{
Uri uri=ContentUris.withAppendedId(Student.CONTENT_URI,id);
resolver=this.getContentResolver();
ContentValues values=new ContentValues();
values.put(Student.NMAE,"xiaofang");
values.put(Student.GENDER,"女");
values.put(Student.AGE, 25);
resolver.update(uri,values,null, null);
}
//查询
public voidquery()
{
Uri uri=Student.CONTENT_URI;
String[] PROJECTION=newString[]{
Student._ID,
Student.NMAE,
Student.GENDER,
Student.AGE
};
resolver=this.getContentResolver();
Cursor cursor=resolver.query(uri, PROJECTION, null,null,null);
//判断游标是否为空
if(cursor.moveToFirst())
{
for(int i=0;i<cursor.getCount();i++)
{
cursor.moveToPosition(i);
int id=cursor.getInt(0);//获得id
String name=cursor.getString(1);//取得姓名
String gender=cursor.getString(2);//取得性别
int age=cursor.getInt(3);//取得年龄
//输出日记
Log.i(TAG,"id:"+id+" name:"+name+" gender:"+gender+" age:"+age);
}
}
}
}

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