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  • ContentProvider

    工作中遇到了contentprovider数据共享机制，下面来总结一下：

    一、ContentProvider简介
           当应用继承ContentProvider类，并重写该类用于提供数据和存储数据的方法，就可以向其他应用共享其数据。虽然使用其他方法也可以对外共享数据，但数据访问方式会因数据存储的方式而不同，如：采用文件方式对外共享数据，需要进行文件操作读写数据；采用sharedpreferences共享数据，需要使用sharedpreferences API读写数据。而使用ContentProvider共享数据的好处是统一了数据访问方式。
    二、Uri类简介
           Uri代表了要操作的数据，Uri主要包含了两部分信息：1.需要操作的ContentProvider ，2.对ContentProvider中的什么数据进行操作，一个Uri由以下几部分组成：

           1.scheme：ContentProvider（内容提供者）的scheme已经由Android所规定为：content://。
           2.主机名（或Authority）：用于唯一标识这个ContentProvider，外部调用者可以根据这个标识来找到它。
           3.路径（path）：可以用来表示我们要操作的数据，路径的构建应根据业务而定，如下：
    •         要操作contact表中id为10的记录，可以构建这样的路径:/contact/10
    •         要操作contact表中id为10的记录的name字段， contact/10/name
    •         要操作contact表中的所有记录，可以构建这样的路径:/contact
    要操作的数据不一定来自数据库，也可以是文件等他存储方式，如下:
    要操作xml文件中contact节点下的name节点，可以构建这样的路径：/contact/name
    如果要把一个字符串转换成Uri，可以使用Uri类中的parse()方法，如下：
    Uri uri = Uri.parse("content://com.changcheng.provider.contactprovider/contact")
    三、UriMatcher、ContentUrist和ContentResolver简介
           因为Uri代表了要操作的数据，所以我们很经常需要解析Uri，并从Uri中获取数据。Android系统提供了两个用于操作Uri的工具类，分别为UriMatcher 和ContentUris 。掌握它们的使用，会便于我们的开发工作。

           UriMatcher：用于匹配Uri，它的用法如下：
           1.首先把你需要匹配Uri路径全部给注册上，如下：
           //常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码(-1)。
           UriMatcher  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
           //如果match()方法匹配content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回匹配码为1
           uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact”, 1);//添加需要匹配uri，如果匹配就会返回匹配码
           //如果match()方法匹配   content://com.changcheng.sqlite.provider.contactprovider/contact/230路径，返回匹配码为2
           uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact/#”, 2);//#号为通配符
          
           2.注册完需要匹配的Uri后，就可以使用uriMatcher.match(uri)方法对输入的Uri进行匹配，如果匹配就返回匹配码，匹配码是调用addURI()方法传入的第三个参数，假设匹配content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回的匹配码为1。

           ContentUris：用于获取Uri路径后面的ID部分，它有两个比较实用的方法：
    •         withAppendedId(uri, id)用于为路径加上ID部分
    •         parseId(uri)方法用于从路径中获取ID部分

           ContentResolver：当外部应用需要对ContentProvider中的数据进行添加、删除、修改和查询操作时，可以使用ContentResolver 类来完成，要获取ContentResolver 对象，可以使用Activity提供的getContentResolver()方法。 ContentResolver使用insert、delete、update、query方法，来操作数据。
    四、ContentProvider示例程序
    Manifest.xml中的代码：
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    <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>中为provider进行注册！！！！
    首先定义一个数据库的工具类：

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    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"); 
    }
    1. 然后创建一个数据库：
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      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);
              }
      }
    1. 接着创建一个Myprovider.java对数据库的接口进行包装：
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      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;
              }
      }


      最后创建测试类：
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      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);
                      //先对数据库进行添加数据
                  dBlite1.add(email,username,date,sex);
                  //通过contentResolver进行查找
                   contentResolver = TestWebviewDemo.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(
                          TestWebviewDemo.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);  //查找后关闭游标
                  }
              }

      注：上面是在一个程序中进行的测试，也可以再新建一个工程来模拟一个新的程序，然后将上面查询的代码加到新的程序当中！这样就模拟了contentprovider的数据共享功能了！
      新建个工程：TestProvider
      创建一个测试的activity
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      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);
                      
                  //通过contentResolver进行查找
                    contentResolver = TestWebviewDemo.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(TestWebviewDemo.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);  //查找后关闭游标
                  }
              }
      运行此程序就能实现共享数据查询了！

      注：新建的程序中的manifest.xml中不需要对provider进行注册，直接运行就行，否则会报错！
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  • 原文地址：https://www.cnblogs.com/it-tomorrow/p/3342636.html
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