ContentProvider简要-白红宇

ContentProvider简要

阅读量：5807 次

发布时间：2019-06-18

本文共 15978 字，大约阅读时间需要 53 分钟。

1．什么是ContentProvider
数据库在Android其中是私有的，当然这些数据包含文件数据和数据库数据以及一些其它类型的数据。

不能将数据库设为

WORLD_READABLE

,每一个数据库都仅仅能创建它的包訪问，
这意味着仅仅有由创建数据库的进程可訪问它。假设须要在进程间传递数据。
则能够使用

AIDL/Binder

或创建一个

ContentProvider

,可是不能跨越进程/包边界直接来使用数据库。

一个

Content Provider

类实现了一组标准的方法接口，从而可以让其它的应用保存或读取此

Content Provider

的各种数据类型。

也就是说，一个程序能够通过实现一个

Content Provider

的抽象接口将自己的数据暴露出去。

外界根本看不到，也不用看到这个应用暴露的数据在应用其中是怎样存储的，或者是用数据库存储还是用文件存储，还是通过网上获得，这些一切都不重要，
重要的是外界能够通过这一套标准及统一的接口和程序里的数据打交道。能够读取程序的数据，也能够删除程序的数据。
当然。中间也会涉及一些权限的问题。下边列举一些较常见的接口。这些接口例如以下所看到的

。

query

（Uri uri, String[] projection, String selection, String[] selectionArgs,String sortOrder）：通过Uri进行查询。返回一个Cursor。

insert

（Uri url, ContentValues values）：将一组数据插入到Uri 指定的地方。

update

（Uri uri, ContentValues values, String where, String[] selectionArgs）：更新Uri指定位置的数据。

delete

（Uri url, String where, String[] selectionArgs）：删除指定Uri而且符合一定条件的数据。

2．什么是ContentResolver

外界的程序通过

ContentResolve

r接口能够訪问

ContentProvider

提供的数据，在Activity其中通过

getContentResolver()

能够得到当前应用的

ContentResolver

实例。
ContentResolver提供的接口和ContentProvider中须要实现的接口相应，主要有下面几个。

query

（Uri uri, String[] projection, String selection, String[] selectionArgs,String sortOrder）：通过Uri进行查询。返回一个Cursor。
·

insert

（Uri url, ContentValues values）：将一组数据插入到Uri 指定的地方。

update

（Uri uri, ContentValues values, String where, String[] selectionArgs）：更新Uri指定位置的数据。

delete

（Uri url, String where, String[] selectionArgs）：删除指定Uri而且符合一定条件的数据。

3．ContentProvider和ContentResolver中用到的Uri

在ContentProvider和 ContentResolver其中用到了Uri的形式通常有两种。一种是指定所有数据。还有一种是指定某个ID的数据。
我们看以下的样例。

content://contacts/people/ 这个Uri指定的就是所有的联系人数据。

· content://contacts/people/1 这个Uri指定的是ID为1的联系人的数据。
在上边两个类中用到的Uri一般由3部分组成。

·  第一部分是方案："content://" 这部分永远不变
·  第二部分是授权："contacts"
·  第二部分是路径："people/","people/1"（假设没有指定ID。那么表示返回所有）。
因为URI通常比較长，并且有时候easy出错，且难以理解。所以，在Android其中定义了一些辅助类，并且定义了一些常量来取代这些长字符串的使用。比例如以下边的代码：
·  Contacts.People.CONTENT_URI （联系人的URI）。

在我们的实例MyProvider中是例如以下定义的：

public static final String AUTHORITY="com.teleca.PeopleProvider";
public static final String PATH_SINGLE="people/#";
public static final String PATH_MULTIPLE="people";
public static final Uri content_URI=Uri.parse("content://"+AUTHORITY+"/"+PATH_MULTIPLE);

实例1：

文件MyProvider.java

package com.teleca.provider;

import java.util.HashMap;

import android.content.ContentProvider;

import android.content.ContentUris;

import android.content.ContentValues;

import android.content.Context;

import android.content.UriMatcher;

import android.database.Cursor;

import android.database.SQLException;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

import android.database.sqlite.SQLiteQueryBuilder;

import android.net.Uri;

import android.text.TextUtils;

import android.util.Log;

public class

MyProvider

extends

ContentProvider {

public static final String MIME_DIR_PREFIX="vnd.android.cursor.dir";

public static final String MIME_ITEM_PREFIX="vnd.android.cursor.item";

public static final String MIME_ITEM="vnd.msi.people";

public static final String MIME_TYPE_SINGLE=MIME_ITEM_PREFIX+"/"+MIME_ITEM;

public static final String MIME_TYPE_MULTIPLE=MIME_DIR_PREFIX+"/"+MIME_ITEM;

public static final String AUTHORITY="com.teleca.PeopleProvider";

public static final String

PATH_SINGLE

="people/#";

public static final String

PATH_MULTIPLE

="people";

public static final Uri content_URI=Uri.parse("content://"+AUTHORITY+"/"+PATH_MULTIPLE);

public static final String DEFAULT_SORT_ORDER="name DESC";

public static final String _ID="_id";

public static final String NAME="name";

public static final String PHONE="phone";

public static final String AGE="age";

public static final int PEOPLE=1;

public static final int PEOPLES=2;

private static UriMatcher URI_MATCHER;

private static HashMap<String,String> PROJECTION_MAP;

public static String DB_NAME="peopledb";

public static String DB_TABLE_NAME="people";

SQLiteDatabase db;

DBOpenHelper dbOpenHelper;

static

{

URI_MATCHER=new UriMatcher(UriMatcher.NO_MATCH);

URI_MATCHER.addURI(AUTHORITY, PATH_MULTIPLE, PEOPLES);

URI_MATCHER.addURI(AUTHORITY, PATH_SINGLE, PEOPLE);

PROJECTION_MAP=new HashMap<String,String>();

PROJECTION_MAP.put(_ID, "_id");

PROJECTION_MAP.put(NAME, "name");

PROJECTION_MAP.put(PHONE, "phone");

PROJECTION_MAP.put(AGE, "age");

}

@Override

public int

delete

(Uri uri, String selection, String[] selectionArgs) {

// TODO Auto-generated method stub

int

count=0;

switch

(URI_MATCHER.match(uri))

{

case

PEOPLES:

count=db.delete(DB_TABLE_NAME, selection, selectionArgs);

break;

case

PEOPLE:

String segment =uri.getPathSegments().get(1);

String where="";

(!TextUtils.isEmpty(selection))

{

where=" AND ("+selection+")";

}

count=db.delete(DB_TABLE_NAME, "_id="+segment+where, selectionArgs);

break

;

default

throw

new IllegalArgumentException("Unkonw URI"+uri);

}

getContext().getContentResolver().notifyChange(uri, null);//@2

return

count;

}

@Override

public

String getType(Uri uri) {

// TODO Auto-generated method stub

switch

(URI_MATCHER.match(uri))

{

case

PEOPLES:

return

MIME_TYPE_MULTIPLE;

case

PEOPLE:

return

MIME_TYPE_SINGLE;

default

throw

new IllegalArgumentException("Unkown URI "+uri);

}

@Override

public Uri insert(Uri uri, ContentValues values) {

// TODO Auto-generated method stub

long rowId=0L;

(URI_MATCHER.match(uri)!=PEOPLES)

{

throw

new IllegalArgumentException("Unkown URI"+uri);

}

rowId=db.insert(DB_TABLE_NAME, null, values);

(rowId>0)

{

Uri result=ContentUris.withAppendedId(content_URI, rowId);

getContext().getContentResolver().notifyChange(result, null);//@2

return

result;

}

else

throw new SQLException("Failed to insert row into "+uri);

}

@Override

public boolean onCreate() {

// TODO Auto-generated method stub

dbOpenHelper=new DBOpenHelper(this.getContext(),DB_NAME,1);

db=dbOpenHelper.getWritableDatabase();

return

false;

}

@Override

public Cursor

query

(Uri uri, String[] projection, String selection,

String[] selectionArgs, String sortOrder) {

// TODO Auto-generated method stub

SQLiteQueryBuilder queryBuilder=new SQLiteQueryBuilder();

queryBuilder.setTables(DBInfo.DB_TABLE_NAME);

queryBuilder.setProjectionMap(PROJECTION_MAP);

switch

(URI_MATCHER.match(uri))
{

case

PEOPLES:
break;

case

  PEOPLE:
   queryBuilder.appendWhere("_id="+uri.getPathSegments().get(1));
   break;

default

:
   throw new IllegalArgumentException("Unkonw URI"+uri);
  }
  String orderBy=null;

(TextUtils.isEmpty(sortOrder))
{

   orderBy=DEFAULT_SORT_ORDER;
  }

else

orderBy=sortOrder;

Cursor c=queryBuilder.query(db, projection, selection, selectionArgs, null, null, orderBy);

c.setNotificationUri(getContext().getContentResolver(), uri);

//@1

return

}

@Override

public int

update

(Uri uri, ContentValues values, String selection,

String[] selectionArgs) {

// TODO Auto-generated method stub

int count=0;

switch

(URI_MATCHER.match(uri))

{

case

PEOPLES:

count=db.update(DB_TABLE_NAME, values, selection, selectionArgs);

break;

case

PEOPLE:

String segment =uri.getPathSegments().get(1);

String where="";

(!TextUtils.isEmpty(selection))

{

where=" AND ("+selection+")";

}

count=db.update(DB_TABLE_NAME, values, "_id="+segment+where, selectionArgs);

break

;

default

throw

new IllegalArgumentException("Unkonw URI"+uri);

}

getContext().getContentResolver().notifyChange(uri, null);//@2

return

count;

}

class

DBOpenHelper

extends SQLiteOpenHelper

{

private static final String

DB_CREATE="CREATE TABLE "

+DBInfo.DB_TABLE_NAME

+" (

_id INTEGER PRIMARY KEY,name TEXT UNIQUE NOT NULL,"

phone TEXT,age INTEGER);";

final static String tag="hubin";

public

DBOpenHelper(Context context,String dbName,int version)

{

super(context,dbName,null,version);

}

public void

onCreate(SQLiteDatabase db)

{

try{

db.execSQL(DB_CREATE);

}

catch(SQLException e )

{

Log.e(tag,"",e);

}

public void onOpen(SQLiteDatabase db)

{

super.onOpen(db);

}

public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion)

{

db.execSQL("DROP TABLE IF EXISTS "+DBInfo.DB_TABLE_NAME);

this.onCreate(db);

}

class DBInfo

{

public static String DB_NAME="peopledb";

public static String DB_TABLE_NAME="people";

}

注意1：c.setNotificationUri(getContext().getContentResolver(), uri);

这里是把Cursor C加入到ContentResolver的监督对象组中去。

一旦有与uri相关的变化。ContentResolver就回通知Cursor C.

可能Cursor有个私有的内部类ContentObserver的实现。ContentResolver是通过该类来通知Cursor的。

public abstract void

setNotificationUri

(ContentResolver cr, Uri uri)
Register to watch a content URI for changes. This can be the URI of a specific data row (for example, "content://my_provider_type/23"),
or a a generic URI for a content type.

Parameters

cr The content resolver from the caller's context. The listener attached to this resolver will be notified.

uri The content URI to watch.

注意2：

getContext().getContentResolver().notifyChange(uri, null)

通知数据发生了变化。

public void notifyChange (Uri uri, ContentObserver observer)
Notify registered observers that a row was updated. To register, call registerContentObserver(). By default, CursorAdapter objects will get this notification.
Parameters
observer The observer that originated the change, may be null
这里为null的意思可能就是调用在ContentResolver中注冊的ContentObserver，反之则是调用參数指定的
文件People.java
package com.teleca.provider;
public class People {

public long id;
public String name;
public String phone;
public int age;
}
文件
Hello.java
package com.teleca.provider;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class Hello extends Activity {

    /** Called when the activity is first created. */
final static String tag="hubin";
    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
  Button button = (Button) findViewById(R.id.Button01);
  OnClickListener listener = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_ADD;
    doAction();
   }
  };
  button.setOnClickListener(listener);
  Button button2 = (Button) findViewById(R.id.Button02);
  OnClickListener listener2 = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_UPDATE;
    doAction();
   }
  };
  button2.setOnClickListener(listener2);
  Button button3 = (Button) findViewById(R.id.Button03);
  OnClickListener listener3 = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_QUERY;
    doAction();
   }
  };
  button3.setOnClickListener(listener3);
  Button button4 = (Button) findViewById(R.id.Button04);
  OnClickListener listener4 = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_QUERY_ALL;
    doAction();
   }
  };
  button4.setOnClickListener(listener4);
  Button button5 = (Button) findViewById(R.id.Button05);
  OnClickListener listener5 = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_DELETE;
    doAction();
   }
  };
  button5.setOnClickListener(listener5);
  Button button6 = (Button) findViewById(R.id.Button06);
  OnClickListener listener6 = new OnClickListener() {

@Override
public void onClick(View v) {

    cmd = CMD_DELETE_ALL;
    doAction();
   }
  };
  button6.setOnClickListener(listener6);
  mHandler = new Handler();
    }
int cnt = 0;
private Handler mHandler;
int cmd = 0;
final int CMD_ADD = 1;
final int CMD_UPDATE = 2;
final int  CMD_QUERY= 3;
final int CMD_QUERY_ALL = 4;
final int CMD_DELETE = 5;
final int CMD_DELETE_ALL = 6;
People people=new People();
final static String projection[]=new String[]
                                       {"_id","name","phone","age"};
class DatabaseThread implements Runnable {

public void run() {

if (cmd == CMD_ADD) {

    people.name="robin"+System.currentTimeMillis()%100;
    people.phone=""+System.currentTimeMillis();
    people.age=1;
    ContentValues values=new ContentValues();
    values.put("name", people.name);
    values.put("phone", people.phone);
    values.put("age", people.age);
    Uri uri=getContentResolver().insert(MyProvider.content_URI, values);
    people.id=ContentUris.parseId(uri);
    Log.i("hubin",uri.toString());
   } else if (cmd == CMD_UPDATE) {

    ContentValues values=new ContentValues();
    people.phone=""+System.currentTimeMillis();
    values.put("phone", people.phone);
    Uri uri=ContentUris.withAppendedId(MyProvider.content_URI, people.id);
    getContentResolver().update(uri,values,null,null);
   } else if (cmd == CMD_QUERY) {

    Uri uri=ContentUris.withAppendedId(MyProvider.content_URI, people.id);
    Cursor c=getContentResolver().query(uri, projection, null, null, null);
    People p=get(c);
    printPeople(p);
   } else if (cmd == CMD_QUERY_ALL) {

    Uri uri=MyProvider.content_URI;
    Cursor c=getContentResolver().query(uri, projection, null, null, null);
    List<People> list=getAll(c);
    int total=list.size();
    for(int i=0;i<total;i++)
    {

     printPeople(list.get(i));
    }
   }
   else if (cmd==CMD_DELETE)
   {

    Uri uri=ContentUris.withAppendedId(MyProvider.content_URI, people.id);
    getContentResolver().delete(uri, null, null);
   }
   else if (cmd==CMD_DELETE_ALL)
   {

    Uri uri=MyProvider.content_URI;
    getContentResolver().delete(uri, null, null);
   }
   cnt++;
  }
}
void printPeople(People p)
{

Log.i(tag, "id:"+p.id);
Log.i(tag, "name:"+p.name);
Log.i(tag,"phone:"+p.phone);
Log.i(tag,"age:"+p.age);
}
DatabaseThread dataDealer=new DatabaseThread();
void doAction() {

mHandler.post(dataDealer);
}
public People get(Cursor c)
{

People people=new People();
try{

   Log.i(tag,"count:"+c.getCount());
   if(c.getCount()>0)
   {

    c.moveToFirst();
    people=new People();
    people.id=c.getLong(0);
    people.name=c.getString(1);
    people.phone=c.getString(2);
    people.age=c.getInt(3);
   }
  }catch(SQLException e)
  {

   Log.i(tag,"",e);
  }
  finally
  {

if(c!=null&&!c.isClosed())
{

    c.close();
   }
  }
  return people;
}
public List<People> getAll(Cursor c)
{

  ArrayList<People> ret=new ArrayList<People>();
  try
  {

   int count=c.getCount();
   c.moveToFirst();
   People people;
   for(int i=0;i<count;i++)
   {

    people=new People();
    people.id=c.getLong(0);
    people.name=c.getString(1);
    people.phone=c.getString(2);
    people.age=c.getInt(3);
    ret.add(people);
    c.moveToNext();
   }

  }catch(SQLException e)
  {

   Log.i(tag,"",e);
  }
  finally
  {

if(c!=null&&!c.isClosed())
{

    c.close();
   }
  }
  return ret;
}
}
注意：Cursor c不用时要关掉。
文件AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android=""
      package="com.teleca.provider"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".Hello"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    <provider android:syncable="true" android:name="MyProvider" android:authorities="com.teleca.PeopleProvider"></provider>
</application>
    <uses-sdk android:minSdkVersion="7" />
</manifest>

list_row.xml文件

<?xml version="1.0" encoding="utf-8"?>

main.xml文件

xml version="1.0" encoding="utf-8"?>