在正式開始實例演示之前,我們先來了解以下兩個知識點:
授權:
在Android中,每一個ContentProvider都會用類似於域名的字符串來註冊自己,我們成爲授權(authority)。這個唯一標識的字符串是此ContentProvider可提供的一組URI的基礎,有了這個基礎,才能夠向外界提供信息的共享服務。
授權是在AndroidManifest.xml中完成的,每一個ContentProvider必須在此聲明並授權,方式如下:
- <provider android:name=".SomeProvider"
- android:authorities="com.your-company.SomeProvider"/>
MIME類型:
就像網站返回給定URL的MIME(Multipurpose Internet Mail Extensions,多用途Internet郵件擴展)類型一樣(這使瀏覽器能夠用正確的程序來查看內容),ContentProvider還負責返回給定URI的MIME類型。根據MIME類型規範,MIME類型包含兩部分:類型和子類型。例如:text/html,text/css,text/xml等等。
Android也遵循類似的約定來定義MIME類型。
對於單條記錄,MIME類型類似於:
vnd.android.cursor.item/vnd.your-company.content-type
而對於記錄的集合,MIME類型類似於:
vnd.android.cursor.dir/vnd.your-company.comtent-type
其中的vnd表示這些類型和子類型具有非標準的、供應商特定的形式;content-type可以根據ContentProvider的功能來定,比如日記的ContentProvider可以爲note,日程安排的ContentProvider可以爲schedule,等等。
瞭解了以上兩個知識點之後,我們就結合實例來演示一下具體的過程。
我們將會創建一個記錄person信息的ContentProvider,實現對person的CRUD操作,訪問者可以通過下面路徑操作我們的ContentProvider:
訪問者可以通過“[BASE_URI]/persons”來操作person集合,也可以通過“[BASE_URI]/persons/#”的形式操作單個person。
我們創建一個person的ContentProvider需要兩個步驟:
1.創建PersonProvider類:
我們需要繼承ContentProvider類,實現onCreate、query、insert、update、delete和getType這幾個方法。具體代碼如下:
- package com.scott.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;
- public class PersonProvider extends ContentProvider {
- private static final UriMatcher matcher;
- private DBHelper helper;
- private SQLiteDatabase db;
- private static final String AUTHORITY = "com.scott.provider.PersonProvider";
- private static final int PERSON_ALL = 0;
- private static final int PERSON_ONE = 1;
- public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.scott.person";
- public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.scott.person";
- //數據改變後立即重新查詢
- private static final Uri NOTIFY_URI = Uri.parse("content://" + AUTHORITY + "/persons");
- static {
- matcher = new UriMatcher(UriMatcher.NO_MATCH);
- matcher.addURI(AUTHORITY, "persons", PERSON_ALL); //匹配記錄集合
- matcher.addURI(AUTHORITY, "persons/#", PERSON_ONE); //匹配單條記錄
- }
- @Override
- public boolean onCreate() {
- helper = new DBHelper(getContext());
- return true;
- }
- @Override
- public String getType(Uri uri) {
- int match = matcher.match(uri);
- switch (match) {
- case PERSON_ALL:
- return CONTENT_TYPE;
- case PERSON_ONE:
- return CONTENT_ITEM_TYPE;
- default:
- throw new IllegalArgumentException("Unknown URI: " + uri);
- }
- }
- @Override
- public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
- db = helper.getReadableDatabase();
- int match = matcher.match(uri);
- switch (match) {
- case PERSON_ALL:
- //doesn't need any code in my provider.
- break;
- case PERSON_ONE:
- long _id = ContentUris.parseId(uri);
- selection = "_id = ?";
- selectionArgs = new String[]{String.valueOf(_id)};
- break;
- default:
- throw new IllegalArgumentException("Unknown URI: " + uri);
- }
- return db.query("person", projection, selection, selectionArgs, null, null, sortOrder);
- }
- @Override
- public Uri insert(Uri uri, ContentValues values) {
- int match = matcher.match(uri);
- if (match != PERSON_ALL) {
- throw new IllegalArgumentException("Wrong URI: " + uri);
- }
- db = helper.getWritableDatabase();
- if (values == null) {
- values = new ContentValues();
- values.put("name", "no name");
- values.put("age", "1");
- values.put("info", "no info.");
- }
- long rowId = db.insert("person", null, values);
- if (rowId > 0) {
- notifyDataChanged();
- return ContentUris.withAppendedId(uri, rowId);
- }
- return null;
- }
- @Override
- public int delete(Uri uri, String selection, String[] selectionArgs) {
- db = helper.getWritableDatabase();
- int match = matcher.match(uri);
- switch (match) {
- case PERSON_ALL:
- //doesn't need any code in my provider.
- break;
- case PERSON_ONE:
- long _id = ContentUris.parseId(uri);
- selection = "_id = ?";
- selectionArgs = new String[]{String.valueOf(_id)};
- }
- int count = db.delete("person", selection, selectionArgs);
- if (count > 0) {
- notifyDataChanged();
- }
- return count;
- }
- @Override
- public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
- db = helper.getWritableDatabase();
- int match = matcher.match(uri);
- switch (match) {
- case PERSON_ALL:
- //doesn't need any code in my provider.
- break;
- case PERSON_ONE:
- long _id = ContentUris.parseId(uri);
- selection = "_id = ?";
- selectionArgs = new String[]{String.valueOf(_id)};
- break;
- default:
- throw new IllegalArgumentException("Unknown URI: " + uri);
- }
- int count = db.update("person", values, selection, selectionArgs);
- if (count > 0) {
- notifyDataChanged();
- }
- return count;
- }
- //通知指定URI數據已改變
- private void notifyDataChanged() {
- getContext().getContentResolver().notifyChange(NOTIFY_URI, null);
- }
- }
在我們的PersonProvider中,我們用到了Person、DBHelper類,代碼如下:
- package com.scott.provider;
- public class Person {
- public int _id;
- public String name;
- public int age;
- public String info;
- public Person() {
- }
- public Person(String name, int age, String info) {
- this.name = name;
- this.age = age;
- this.info = info;
- }
- }
- package com.scott.provider;
- import android.content.Context;
- import android.database.sqlite.SQLiteDatabase;
- import android.database.sqlite.SQLiteOpenHelper;
- public class DBHelper extends SQLiteOpenHelper {
- private static final String DATABASE_NAME = "provider.db";
- private static final int DATABASE_VERSION = 1;
- public DBHelper(Context context) {
- super(context, DATABASE_NAME, null, DATABASE_VERSION);
- }
- @Override
- public void onCreate(SQLiteDatabase db) {
- String sql = "CREATE TABLE IF NOT EXISTS person" +
- "(_id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, age INTEGER, info TEXT)";
- db.execSQL(sql);
- }
- @Override
- public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
- db.execSQL("DROP TABLE IF EXISTS person");
- onCreate(db);
- }
- }
最後,要想讓這個ContentProvider生效,我們需要在AndroidManifest.xml中聲明併爲其授權,如下所示:
- <provider android:name=".PersonProvider"
- android:authorities="com.scott.provider.PersonProvider"
- android:multiprocess="true"/>
其中,android:multiprocess代表是否允許多進程操作。另外我們也可以爲其聲明相應的權限,對應的屬性是:android:permission。
2.調用PersonProvider類:
完成了person的ContentProvider後,下面我們來看一下如何訪問它。這一步我們在MainActivity中完成,看下面代碼:
- package com.scott.provider;
- import java.util.ArrayList;
- import android.app.Activity;
- import android.content.ContentResolver;
- import android.content.ContentUris;
- import android.content.ContentValues;
- import android.database.Cursor;
- import android.database.CursorWrapper;
- import android.net.Uri;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.Message;
- import android.view.View;
- import android.widget.ListView;
- import android.widget.SimpleCursorAdapter;
- public class MainActivity extends Activity {
- private ContentResolver resolver;
- private ListView listView;
- private static final String AUTHORITY = "com.scott.provider.PersonProvider";
- private static final Uri PERSON_ALL_URI = Uri.parse("content://" + AUTHORITY + "/persons");
- private Handler handler = new Handler() {
- public void handleMessage(Message msg) {
- //update records.
- requery();
- };
- };
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- resolver = getContentResolver();
- listView = (ListView) findViewById(R.id.listView);
- //爲PERSON_ALL_URI註冊變化通知
- getContentResolver().registerContentObserver(PERSON_ALL_URI, true, new PersonObserver(handler));
- }
- /**
- * 初始化
- * @param view
- */
- public void init(View view) {
- ArrayList<Person> persons = new ArrayList<Person>();
- Person person1 = new Person("Ella", 22, "lively girl");
- Person person2 = new Person("Jenny", 22, "beautiful girl");
- Person person3 = new Person("Jessica", 23, "sexy girl");
- Person person4 = new Person("Kelly", 23, "hot baby");
- Person person5 = new Person("Jane", 25, "pretty woman");
- persons.add(person1);
- persons.add(person2);
- persons.add(person3);
- persons.add(person4);
- persons.add(person5);
- for (Person person : persons) {
- ContentValues values = new ContentValues();
- values.put("name", person.name);
- values.put("age", person.age);
- values.put("info", person.info);
- resolver.insert(PERSON_ALL_URI, values);
- }
- }
- /**
- * 查詢所有記錄
- * @param view
- */
- public void query(View view) {
- // Uri personOneUri = ContentUris.withAppendedId(PERSON_ALL_URI, 1);查詢_id爲1的記錄
- Cursor c = resolver.query(PERSON_ALL_URI, null, null, null, null);
- CursorWrapper cursorWrapper = new CursorWrapper(c) {
- @Override
- public String getString(int columnIndex) {
- //將簡介前加上年齡
- if (getColumnName(columnIndex).equals("info")) {
- int age = getInt(getColumnIndex("age"));
- return age + " years old, " + super.getString(columnIndex);
- }
- return super.getString(columnIndex);
- }
- };
- //Cursor須含有"_id"字段
- SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2,
- cursorWrapper, new String[]{"name", "info"}, new int[]{android.R.id.text1, android.R.id.text2});
- listView.setAdapter(adapter);
- startManagingCursor(cursorWrapper); //管理Cursor
- }
- /**
- * 插入一條記錄
- * @param view
- */
- public void insert(View view) {
- Person person = new Person("Alina", 26, "attractive lady");
- ContentValues values = new ContentValues();
- values.put("name", person.name);
- values.put("age", person.age);
- values.put("info", person.info);
- resolver.insert(PERSON_ALL_URI, values);
- }
- /**
- * 更新一條記錄
- * @param view
- */
- public void update(View view) {
- Person person = new Person();
- person.name = "Jane";
- person.age = 30;
- //將指定name的記錄age字段更新爲30
- ContentValues values = new ContentValues();
- values.put("age", person.age);
- resolver.update(PERSON_ALL_URI, values, "name = ?", new String[]{person.name});
- //將_id爲1的age更新爲30
- // Uri updateUri = ContentUris.withAppendedId(PERSON_ALL_URI, 1);
- // resolver.update(updateUri, values, null, null);
- }
- /**
- * 刪除一條記錄
- * @param view
- */
- public void delete(View view) {
- //刪除_id爲1的記錄
- Uri delUri = ContentUris.withAppendedId(PERSON_ALL_URI, 1);
- resolver.delete(delUri, null, null);
- //刪除所有記錄
- // resolver.delete(PERSON_ALL_URI, null, null);
- }
- /**
- * 重新查詢
- */
- private void requery() {
- //實際操作中可以查詢集合信息後Adapter.notifyDataSetChanged();
- query(null);
- }
- }
在前面的PersonProvider我們也提到,在數據更改後,會向指定的URI訪問者發出通知,以便於更新查詢記錄。大家注意,僅僅是ContentProvider出力還不夠,我們還需要在訪問者中註冊一個ContentObserver,才能夠接收到這個通知。下面我們創建一個PersonObserver:
- package com.scott.provider;
- import android.database.ContentObserver;
- import android.os.Handler;
- import android.os.Message;
- import android.util.Log;
- public class PersonObserver extends ContentObserver {
- public static final String TAG = "PersonObserver";
- private Handler handler;
- public PersonObserver(Handler handler) {
- super(handler);
- this.handler = handler;
- }
- @Override
- public void onChange(boolean selfChange) {
- super.onChange(selfChange);
- Log.i(TAG, "data changed, try to requery.");
- //向handler發送消息,更新查詢記錄
- Message msg = new Message();
- handler.sendMessage(msg);
- }
- }
最後,我們要在AndroidManifest.xml中爲MainActivity添加MIME類型過濾器,告訴系統MainActivity可以處理的信息類型:
- <!-- MIME類型 -->
- <intent-filter>
- <data android:mimeType="vnd.android.cursor.dir/vnd.scott.person"/>
- </intent-filter>
- <intent-filter>
- <data android:mimeType="vnd.android.cursor.item/vnd.scott.person"/>
- </intent-filter>
鑑於操作類型太多,我在這裏就不再展示了,大家可以自己試一試。