Android学习---通过内容提供者(ContentProvider)操作另外一个应用私有数据库的内容...

一.什么是ContentProvider?

ContentProvider直译过来就是内容提供者,主要作用就是A应用提供接口给B应用调用数据,和之前介绍的sharedPreference和直接开放文件访问类似,都是共享应用程序数据,不同的是之前的两种文件格式可能完全不同,如可能为xml,txt,sql等等,这里ContentProvider返回的数据格式是统一的,因此应用的更为广泛一点.

二.实例

这里使用的是A应用通过ContentProvider共享数据给B应用.这里A应用用的是前文中的android_db里的person表.B应用是新建的android_content_provider程序.

１.新创建android_content_provider应用程序

2.访问android_db共享的数据

创建好了应用程序以后,

/android_content_provider/src/com/example/android_content_provider/ContentProvider.java

package com.example.android_content_provider;import android.app.Activity;
import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;public class ContentProvider extends Activity {private static String tag = "ContentProvider.class";/*** Called when the activity is first created.*/@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);//内容解析者ContentResolver contentResolver = getContentResolver();Uri uri = Uri.parse("content://com.amos.android_db.provider.PersonProvider/persons");Cursor cursor = contentResolver.query(uri, null, null, null, null);while(cursor.moveToNext()){String name = cursor.getString(cursor.getColumnIndex("name"));int age = cursor.getInt(cursor.getColumnIndex("age"));System.out.println("name:"+name+" age:"+age);Log.d(tag,"用户名:"+name+" 年龄:"+age);}}
}

3.android_db开放共享数据接口

1)开放一个uri

/android_db/AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.amos.android_db"android:versionCode="1"android:versionName="1.0"><instrumentation android:name="android.test.InstrumentationTestRunner"android:targetPackage="com.amos.android_db"></instrumentation><uses-sdk android:minSdkVersion="7"/><application android:label="@string/app_name"><uses-library android:name="android.test.runner"/><activity android:name="MyActivity"android:label="@string/app_name"><intent-filter><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></intent-filter></activity>  <!--给内容提供者提供定义一个uri,一般建议使用包名+类名,以供其它程序调用 --><provider android:authorities="com.amos.android_db.provider.PersonProvider" android:name=".provider.PersonProvider">
</provider></application>
</manifest>

2).定义路径匹配(继承ContentProvider类)

/android_db/src/com/amos/android_db/provider/PersonProvider.java

package com.amos.android_db.provider;import android.content.ContentProvider;
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.util.Log;
import com.amos.android_db.MyDBHelper;
import com.amos.android_db.dao.Person;
import com.amos.android_db.dao.PersonDao;import java.util.List;/*** Created by amosli on 14-6-17.*/
public class PersonProvider extends ContentProvider {//创建一个路径识别器//常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码,也就是说如果找不到匹配的类型,返回-1private static final UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);private static final int ALL_PERSON = 1;private static final int PERSON = 2;private static final int OTHER = 3;private static String tag="PersonProvider.class";static{//1.指定一个路径的匹配规则//如果路径满足content://com.amos.android_db.provider.PersonProvider/persons,返回值就是(ALL_PERSON)=1uriMatcher.addURI("com.amos.android_db.provider.PersonProvider","persons",ALL_PERSON);//2.如果路径满足content://com.amos.android_db.provider.PersonProvider/person/3,返回值就是(PERSON)=2//#号为通配符uriMatcher.addURI("com.amos.android_db.provider.PersonProvider","person/#",PERSON);//3.如果路径满足content://com.amos.android_db.provider.PersonProvider/other,返回值就是(OTHER)=3uriMatcher.addURI("com.amos.android_db.provider.PersonProvider","other",OTHER);}/*** 一般是对象第一次被创建时调用的方法** @return*/@Overridepublic boolean onCreate() {return false;}/*** 让别人去调用返回结果** @param uri* @param projection    选择的列* @param selection     查询条件* @param selectionArgs 查询条件的value* @param sortOrder     排序* @return*/@Overridepublic Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {int result = uriMatcher.match(uri);switch(result){//如果路径满足content://com.amos.android_db.provider.PersonProvider/persons,返回值就是(ALL_PERSON)=1case ALL_PERSON:PersonDao dao = new PersonDao(this.getContext());return dao.findAllByCursor();//2.如果路径满足content://com.amos.android_db.provider.PersonProvider/person/3,返回值就是(PERSON)=2case PERSON:long id = ContentUris.parseId(uri);SQLiteDatabase database = new MyDBHelper(this.getContext()).getReadableDatabase();if(database.isOpen()){database.execSQL("select * person where personid = "+id);return database.query("person", null, "personid", new String[]{id + ""}, null, null, null);//不要关闭数据库,否则就没有数据了.
                }case OTHER:Log.d(tag,"我是其他匹配规则!");break;default:throw new RuntimeException("出错了!!");}return null;}@Overridepublic String getType(Uri uri) {return null;}@Overridepublic Uri insert(Uri uri, ContentValues values) {return null;}@Overridepublic int delete(Uri uri, String selection, String[] selectionArgs) {return 0;}@Overridepublic int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {return 0;}
}

４.效果图

首先,将android_db部署到avd上,其次,运行android_content_provider项目,最后,查看log输出.

5.出现的问题

1).报空指针错误

.....at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.android_content_provider.ContentProvider.onCreate(ContentProvider.java:21)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
.....

这种问题很有可能是路径名称不对,注意提供的接口名称保持一致;并且保证获取数据的接口是正常的,即android_db里获取person表的内容是正常的.

2).intelij中的logcat中看不到log

注意选择Android--->选择要查看Log的进程--->点击上面的双向箭头进行切换日志展示信息.

6.扩展

1),查询,增加,删除,修改的接口全部实现

上面已经实现了查询的接口,这里将实现另外三个接口:

        //4.插入数据,如果路径满足content://com.amos.android_db.provider.PersonProvider/insert,返回值就是(INSERT)=4uriMatcher.addURI("com.amos.android_db.provider.PersonProvider", "insert", INSERT);//5.删除数据,如果路径满足content://com.amos.android_db.provider.PersonProvider/delete,返回值就是(DELETE)=5uriMatcher.addURI("com.amos.android_db.provider.PersonProvider", "delete", DELETE);//6.更新数据,如果路径满足content://com.amos.android_db.provider.PersonProvider/update,返回值就是(UPDATE)=6uriMatcher.addURI("com.amos.android_db.provider.PersonProvider", "update", UPDATE);

对应的实现:

 @Overridepublic Uri insert(Uri uri, ContentValues values) {//content://com.amos.android_db.provider.PersonProvider/insertint result = uriMatcher.match(uri);switch (result) {case INSERT:SQLiteDatabase database = myDBHelper.getWritableDatabase();if (database.isOpen()) {database.insert("person", null, values);}return uri;default:throw new RuntimeException("无法识别该URI,出错了!!");}}@Overridepublic int delete(Uri uri, String selection, String[] selectionArgs) {//删除操作//content://com.amos.android_db.provider.PersonProvider/deleteint result = uriMatcher.match(uri);switch (result) {case DELETE:SQLiteDatabase database = myDBHelper.getWritableDatabase();return database.delete("person", selection, selectionArgs);default:throw new RuntimeException("无法识别该URI,出错了!!");}}@Overridepublic int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {//更新操作//content://com.amos.android_db.provider.PersonProvider/updateint result = uriMatcher.match(uri);switch (result) {case UPDATE:SQLiteDatabase database = myDBHelper.getWritableDatabase();return database.update("person", values, selection, selectionArgs);default:throw new RuntimeException("无法识别该URI,出错了!!");}}

//返回值的类型

   @Overridepublic String getType(Uri uri) {int result = uriMatcher.match(uri);switch (result){case ALL_PERSON:return "List<Person>";case PERSON:return "Person";default:return null;}}

2)测试

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.ContentProviderTest"android:versionCode="1"android:versionName="1.0"><uses-sdk android:minSdkVersion="7"/><instrumentation android:name="android.test.InstrumentationTestRunner" android:targetPackage="com.example.ContentProviderTest"/><application android:label="@string/app_name">  <uses-library android:name="android.test.runner"/><activity android:name="MyActivity"android:label="@string/app_name"><intent-filter><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></intent-filter></activity></application>
</manifest>

加入加粗的两行,配置好测试的环境.

/ContentProviderTest/src/com/example/ContentProviderTest/test/TestCase.java

package com.example.ContentProviderTest.test;import android.content.ContentResolver;
import android.content.ContentValues;
import android.net.Uri;
import android.test.AndroidTestCase;/*** Created by amosli on 14-6-19.*/
public class TestCase extends AndroidTestCase {public void testInsert(){ContentResolver contentResolver = getContext().getContentResolver();Uri uri = Uri.parse("content://com.amos.android_db.provider.PersonProvider/insert");ContentValues values = new ContentValues();values.put("name", "bill");values.put("age", 18);contentResolver.insert(uri, values);}public void testDelete(){ContentResolver contentResolver = getContext().getContentResolver();Uri uri = Uri.parse("content://com.amos.android_db.provider.PersonProvider/delete");contentResolver.delete(uri,"name=?",new String[]{"amos96"});}public void testUpdate(){ContentResolver contentResolver = getContext().getContentResolver();Uri uri = Uri.parse("content://com.amos.android_db.provider.PersonProvider/update");ContentValues contentValues = new ContentValues();contentValues.put("name","jack");contentValues.put("age",30);contentResolver.update(uri,contentValues,"name=?",new String[]{"amos97"});}}

3)效果图:

插入数据(insert方法),bill

删除数据(delete方法),amos96

更新数据(update方法 ),amos97

本文源码:

https://github.com/amosli/android_basic/tree/android_db

https://github.com/amosli/android_basic/tree/content_provoider

https://github.com/amosli/android_basic/tree/android_contentProviderTest