contentprovider的學習實例總結

一、ContentProvider簡介
   當應用繼承ContentProvider類，並重寫該類用於提供數據和存儲數據的方法，就可以向其他應用共享其數據。雖然使用其他方法也可以對外共享數據，但數據訪問方式會因數據存儲的方式而不同，如：採用文件方式對外共享數據，需要進行文件操作讀寫數據；採用sharedpreferences共享數據，需要使用sharedpreferences API讀寫數據。而使用ContentProvider共享數據的好處是統一了數據訪問方式。
二、Uri類簡介
   Uri代表了要操作的數據，Uri主要包含了兩部分信息：1.需要操作的ContentProvider ，2.對ContentProvider中的什麼數據進行操作，一個Uri由以下幾部分組成：

   1.scheme：ContentProvider（內容提供者）的scheme已經由Android所規定爲：content://。
   2.主機名（或Authority）：用於唯一標識這個ContentProvider，外部調用者可以根據這個標識來找到它。
   3.路徑（path）：可以用來表示我們要操作的數據，路徑的構建應根據業務而定，如下：
•       要操作contact表中id爲10的記錄，可以構建這樣的路徑:/contact/10
•       要操作contact表中id爲10的記錄的name字段， contact/10/name
•       要操作contact表中的所有記錄，可以構建這樣的路徑:/contact
要操作的數據不一定來自數據庫，也可以是文件等他存儲方式，如下:
要操作xml文件中contact節點下的name節點，可以構建這樣的路徑：/contact/name
如果要把一個字符串轉換成Uri，可以使用Uri類中的parse()方法，如下：
Uri uri = Uri.parse("content://com.changcheng.provider.contactprovider/contact")
三、UriMatcher、ContentUrist和ContentResolver簡介
   因爲Uri代表了要操作的數據，所以我們很經常需要解析Uri，並從Uri中獲取數據。Android系統提供了兩個用於操作Uri的工具類，分別爲UriMatcher 和ContentUris 。掌握它們的使用，會便於我們的開發工作。

   UriMatcher：用於匹配Uri，它的用法如下：
   1.首先把你需要匹配Uri路徑全部給註冊上，如下：
   //常量UriMatcher.NO_MATCH表示不匹配任何路徑的返回碼(-1)。
   UriMatcher  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
   //如果match()方法匹配content://com.changcheng.sqlite.provider.contactprovider/contact路徑，返回匹配碼爲1
   uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact”, 1);//添加需要匹配uri，如果匹配就會返回匹配碼
   //如果match()方法匹配 content://com.changcheng.sqlite.provider.contactprovider/contact/230路徑，返回匹配碼爲2
   uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact/#”, 2);//#號爲通配符

   2.註冊完需要匹配的Uri後，就可以使用uriMatcher.match(uri)方法對輸入的Uri進行匹配，如果匹配就返回匹配碼，匹配碼是調用addURI()方法傳入的第三個參數，假設匹配content://com.changcheng.sqlite.provider.contactprovider/contact路徑，返回的匹配碼爲1。

   ContentUris：用於獲取Uri路徑後面的ID部分，它有兩個比較實用的方法：
•       withAppendedId(uri, id)用於爲路徑加上ID部分
•       parseId(uri)方法用於從路徑中獲取ID部分

   ContentResolver：當外部應用需要對ContentProvider中的數據進行添加、刪除、修改和查詢操作時，可以使用ContentResolver 類來完成，要獲取ContentResolver 對象，可以使用Activity提供的getContentResolver()方法。 ContentResolver使用insert、delete、update、query方法，來操作數據。
四、ContentProvider示例程序
Manifest.xml中的代碼：

<application android:icon="@drawable/icon" android:label="@string/app_name">
                <activity android:name=".TestWebviewDemo" android:label="@string/app_name">
                        <intent-filter>
                                <action android:name="android.intent.action.MAIN" />
                                <category android:name="android.intent.category.LAUNCHER" />
                        </intent-filter>
                        <intent-filter>
                                <data android:mimeType="vnd.android.cursor.dir/vnd.ruixin.login" />
                        </intent-filter>
                        <intent-filter>
                                <data android:mimeType="vnd.android.cursor.item/vnd.ruixin.login" />
                        </intent-filter>
                         
                </activity>
                <provider android:name="MyProvider" android:authorities="com.ruixin.login" />
        </application>

需要在<application></application>中爲provider進行註冊！！！！
首先定義一個數據庫的工具類：

public class RuiXin {
 
        public static final String DBNAME = "ruixinonlinedb"; 
        public static final String TNAME = "ruixinonline";
        public static final int VERSION = 3;
         
        public static String TID = "tid";
        public static final String EMAIL = "email";
        public static final String USERNAME = "username";
        public static final String DATE = "date";
        public static final String SEX = "sex";
         
         
        public static final String AUTOHORITY = "com.ruixin.login";
        public static final int ITEM = 1;
        public static final int ITEM_ID = 2;
         
        public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.ruixin.login";
        public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.ruixin.login";
         
        public static final Uri CONTENT_URI = Uri.parse("content://" + AUTOHORITY + "/ruixinonline");
}

然後創建一個數據庫：

public class DBlite extends SQLiteOpenHelper {
        public DBlite(Context context) {
                super(context, RuiXin.DBNAME, null, RuiXin.VERSION);
                // TODO Auto-generated constructor stub
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
                // TODO Auto-generated method stub
                        db.execSQL("create table "+RuiXin.TNAME+"(" +
                                RuiXin.TID+" integer primary key autoincrement not null,"+
                                RuiXin.EMAIL+" text not null," +
                                RuiXin.USERNAME+" text not null," +
                                RuiXin.DATE+" interger not null,"+
                                RuiXin.SEX+" text not null);");
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
                // TODO Auto-generated method stub
        }
        public void add(String email,String username,String date,String sex){
                SQLiteDatabase db = getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put(RuiXin.EMAIL, email);
                values.put(RuiXin.USERNAME, username);
                values.put(RuiXin.DATE, date);
                values.put(RuiXin.SEX, sex);
                db.insert(RuiXin.TNAME,"",values);
        }
}

接着創建一個Myprovider.java對數據庫的接口進行包裝：

public class MyProvider extends ContentProvider{
 
        DBlite dBlite;
        SQLiteDatabase db;
         
        private static final UriMatcher sMatcher;
        static{
                sMatcher = new UriMatcher(UriMatcher.NO_MATCH);
                sMatcher.addURI(RuiXin.AUTOHORITY,RuiXin.TNAME, RuiXin.ITEM);
                sMatcher.addURI(RuiXin.AUTOHORITY, RuiXin.TNAME+"/#", RuiXin.ITEM_ID);
 
        }
        @Override
        public int delete(Uri uri, String selection, String[] selectionArgs) {
                // TODO Auto-generated method stub
                db = dBlite.getWritableDatabase();
                int count = 0;
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        count = db.delete(RuiXin.TNAME,selection, selectionArgs);
                        break;
                case RuiXin.ITEM_ID:
                        String id = uri.getPathSegments().get(1);
                        count = db.delete(RuiXin.TID, RuiXin.TID+"="+id+(!TextUtils.isEmpty(RuiXin.TID="?")?"AND("+selection+')':""), selectionArgs);
                    break;
                default:
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                getContext().getContentResolver().notifyChange(uri, null);
                return count;
        }
 
        @Override
        public String getType(Uri uri) {
                // TODO Auto-generated method stub
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        return RuiXin.CONTENT_TYPE;
                case RuiXin.ITEM_ID:
                    return RuiXin.CONTENT_ITEM_TYPE;
                default:
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
        }
 
        @Override
        public Uri insert(Uri uri, ContentValues values) {
                // TODO Auto-generated method stub
                 
                db = dBlite.getWritableDatabase();
                long rowId;
                if(sMatcher.match(uri)!=RuiXin.ITEM){
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                rowId = db.insert(RuiXin.TNAME,RuiXin.TID,values);
                   if(rowId>0){
                           Uri noteUri=ContentUris.withAppendedId(RuiXin.CONTENT_URI, rowId);
                           getContext().getContentResolver().notifyChange(noteUri, null);
                           return noteUri;
                   }
                   throw new IllegalArgumentException("Unknown URI"+uri);
        }
 
        @Override
        public boolean onCreate() {
                // TODO Auto-generated method stub
                this.dBlite = new DBlite(this.getContext());
//                db = dBlite.getWritableDatabase();
//                return (db == null)?false:true;
                return true;
        }
 
        @Override
        public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
                // TODO Auto-generated method stub
                db = dBlite.getWritableDatabase();                
                Cursor c;
                Log.d("-------", String.valueOf(sMatcher.match(uri)));
                switch (sMatcher.match(uri)) {
                case RuiXin.ITEM:
                        c = db.query(RuiXin.TNAME, projection, selection, selectionArgs, null, null, null);
                 
                        break;
                case RuiXin.ITEM_ID:
                        String id = uri.getPathSegments().get(1);
                        c = db.query(RuiXin.TNAME, projection, RuiXin.TID+"="+id+(!TextUtils.isEmpty(selection)?"AND("+selection+')':""),selectionArgs, null, null, sortOrder);
                    break;
                default:
                        Log.d("!!!!!!", "Unknown URI"+uri);
                        throw new IllegalArgumentException("Unknown URI"+uri);
                }
                c.setNotificationUri(getContext().getContentResolver(), uri);
                return c;
        }
        @Override
        public int update(Uri uri, ContentValues values, String selection,
                        String[] selectionArgs) {
                // TODO Auto-generated method stub
                return 0;
        }
}

最後創建測試類：

public class Test extends Activity {
    /** Called when the activity is first created. */
   private DBlite dBlite1 = new DBlite(this);;
        private ContentResolver contentResolver;
                    public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
                //先對數據庫進行添加數據
            dBlite1.add(email,username,date,sex);
            //通過contentResolver進行查找
             contentResolver = Test.this.getContentResolver();
            Cursor cursor = contentResolver.query(
                  RuiXin.CONTENT_URI, new String[] {
                  RuiXin.EMAIL, RuiXin.USERNAME,
                  RuiXin.DATE,RuiXin.SEX }, null, null, null);
                while (cursor.moveToNext()) {
                     Toast.makeText(
                    Test.this,
                    cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))
                            + " "
                            + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),
                           Toast.LENGTH_SHORT).show();
                     }
                   startManagingCursor(cursor);  //查找後關閉遊標
            }
        }

注：上面是在一個程序中進行的測試，也可以再新建一個工程來模擬一個新的程序，然後將上面查詢的代碼加到新的程序當中！這樣就模擬了contentprovider的數據共享功能了！
新建個工程：TestProvider

需要把RuiXin類複製進來

創建一個測試的activity

public class Test extends Activity {
    /** Called when the activity is first created. */
        private ContentResolver contentResolver;
                    public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
               
            //通過contentResolver進行查找
              contentResolver = Test.this.getContentResolver();                     
             Cursor cursor = contentResolver.query(
                RuiXin.CONTENT_URI, new String[] {
                RuiXin.EMAIL, RuiXin.USERNAME,
                RuiXin.DATE,RuiXin.SEX }, null, null, null);
            while (cursor.moveToNext()) {
               Toast.makeText(Test.this,
                       cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))
                       + " "
                       + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),
                       Toast.LENGTH_SHORT).show();
                   }
                   startManagingCursor(cursor);  //查找後關閉遊標
            }
        }

運行此程序就能實現共享數據查詢了！

注：新建的程序中的manifest.xml中不需要對provider進行註冊，直接運行就行，否則會報錯！

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