Android的ContentProvider之二 实现自己的ContentProvider

开发只需两步：

1. 开发一个ContentProvider的子类，该子类需要实现query()、insert()、update()和delete()
2. 在AndroidManifest.xml文件中注册该ContentProvider，指定android:authorities属性

<provider
            android:name=".FirstProvider"
            android:authorities="com.example.providers.firstprovider"
            android:exported="true"

            />

示例代码：

first_provider

publicclassFirstProvider extends ContentProvider
{
// 第一次创建该ContentProvider时调用该方法
@Override
publicbooleanonCreate()
{
System.out.println("===onCreate方法被调用===");
returntrue;
}

// 该方法的返回值代表了该ContentProvider所提供数据的MIME类型
@Override
publicString getType(Uri uri)
{
System.out.println("~~getType方法被调用~~");
returnnull;
}

// 实现查询方法，该方法应该返回查询得到的Cursor
@Override
publicCursor query(Uri uri, String[] projection, String where,
String[] whereArgs, String sortOrder)
{
System.out.println(uri +"===query方法被调用===");
System.out.println("where参数为："+ where);
returnnull;
}

// 实现插入的方法，该方法应该新插入的记录的Uri
@Override
publicUri insert(Uri uri, ContentValues values)
{
System.out.println(uri +"===insert方法被调用===");
System.out.println("values参数为："+ values);
returnnull;
}

// 实现删除方法，该方法应该返回被删除的记录条数
@Override
publicintdelete(Uri uri, String where, String[] whereArgs)
{
System.out.println(uri +"===delete方法被调用===");
System.out.println("where参数为："+ where);
return0;
}

// 实现删除方法，该方法应该返回被更新的记录条数
@Override
publicintupdate(Uri uri, ContentValues values, String where,
String[] whereArgs)
{
System.out.println(uri +"===update方法被调用===");
System.out.println("where参数为："
+ where + ",values参数为：" + values);
return0;
}

}

FirstResolver.java

publicclassFirstResolver extends ActionBarActivity {


ContentResolver contentResolver;
Uri uri = Uri.parse("content://com.example.providers.firstprovider/");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        contentResolver = getContentResolver();
    }
    public void query(View source)
    {
    Cursor c = contentResolver.query(
    uri,null,"query_where",null,null);
    Toast.makeText(this,"CP return Cursor :"+ c
    , Toast.LENGTH_SHORT).show();
    }
    public void insert(View source)
    {
    ContentValues values = new ContentValues();
    values.put("name","fkjava");
    Uri newUri = contentResolver.insert(uri, values);
    Toast.makeText(this,"CP insert Uri :"+ newUri
    , Toast.LENGTH_SHORT).show();
    }
    public void update(View source)
    {
    ContentValues values = new ContentValues();
    values.put("name","fkjava");
    intcount = contentResolver.update(uri, values
    ,"update_where",null);
    Toast.makeText(this,"CP update log :"+ count
    , Toast.LENGTH_SHORT).show();
    }
    public void delete(View source)
    {
    intcount = contentResolver.delete(uri
    ,"delete_where",null);
    Toast.makeText(this,"CP delte log :"+ count
    , Toast.LENGTH_SHORT).show();

    }

}

---

android提供了UriMatcher工具类

• void addURI(String authority, String path, int code)：该方法用于向UriMatcher对象注册Uri；（authority与path组合成一个Uri，code则代表Uri对应的标识码）
• int match(Uri uri)：根据前面注册的Uri来判断指定Uri对应的标识码。如果找不到标识码则返回-1

android还提供了ContentUris工具类

• withAppendedId(uri, id)用于为路径加上ID部分
• parseId(uri)：用于从指定Uri中解析出包含的ID值

常常提供工具类，方便维护（在类中定义常用字符串常量）

示例代码如下：

public class DictProvider extends ContentProvider {

     private static UriMathcer matcher = new UriMatcher(UriMaather.NO_MATCH);

     private static final int WORDS = 1;

     private static final int WORD = 2;

     private MyDatabaseHelper dbOpenHelper;

     static {

          matcher.addURI(Words.AUTHORITY, "words", WORDS);

          matcher.addURI(Words.AUTHORITY, "word/#", WORD);

     }

     @Override

     public boolean OnCreate() {

          dbOpenHelper = new MyDatabaseHelper(this.getContext(), "myDict.db3", 1);

          return true;

     }

     @Override

     public String getType(Uri uri) {

          switch (matcher.match(uri)) {

          case WORDS:

               return "vnd.android.cursor.dir/com.example.dict";

          case WORD:

               return "vnd.android.cursor.item/com.example.dict";

          default:

               throw new IllegalArgumentException("unknown Uri:" + uri);

          }

     }

     @Override

     public Cursor query(Uri uri, String[] projection, String where,

               String[] whereArgs, String sortOrder) {

          SQLiteDatabase db = dbOpenHelper.getReadableDatabase();

          switch (matcher.match(uri)) {

          case WORDS:

               return db.query("dict", projection, where, whereArgs, null, null,

                         sortOrder);

          case WORD:

               long id = ContentUris.parseId(uri);

               String whereClause = Words.Word._ID + "=" + id;

               if (where != null && !"".equals(where)) {

                    whereClause = whereClause + " and " + where;

               }

               return db.query("dict", projection, whereClause, whereArgs, null,

                         null, sortOrder);

          default:

               throw new IllegalArgumentException("unknown Uri:" + uri);

          }

     }

     @Override

     public Uri insert(Uri uri, ContentValues values) {

          SQLiteDatabase db = dbOpenHelper.getReadableDatabase();

          switch (matcher.match(uri)) {

          case WORDS:

               long rowId = db.insert("dict", Words.WORD._ID, values);

               if (rowId > 0) {

                    Uri wordUri = ContentUris.withAppendedId(uri, rowId);

                    getContext().getContentResolver().notifyChange(wordUri, null);

                    return wordUri;

               }

               break;

          default:

               throw new IllegalArgumentException("unknown Uri:" + uri);

          }

     }

     @Override

     public int update(Uri uri, ContentValues values, String where,

               String[] whereArgs) {

          SQLiteDatabase db = dbOpenHelper.getReadableDatabase();

          int num = 0;

          switch (matcher.match(uri)) {

          case WORDS:

               num = db.update("dict", values, where, whereArgs);

               break;

          case WORD:

               long id = ContentUris.parseId(uri);

               String whereClause = Words.Word._ID + "=" + id;

               if (where != null && !"".equals(where)) {

                    whereClause = whereClause + " and " + where;

               }

               num = db.update("dict", values, whereClause, whereArgs);

               break;

          default:

               throw new IllegalArgumentException("unknown Uri:" + uri);

               return num;

          }

     }

     @Override

     public int update(Uri uri, ContentValues values, String where,

               String[] whereArgs) {

          SQLiteDatabase db = dbOpenHelper.getReadableDatabase();

          int num = 0;

          switch (matcher.match(uri)) {

          case WORDS:

               num = db.delete("dict", values, where, whereArgs);

               break;

          case WORD:

               long id = ContentUris.parseId(uri);

               String whereClause = Words.Word._ID + "=" + id;

               if (where != null && !"".equals(where)) {

                    whereClause = whereClause + " and " + where;

               }

               num = db.delete("dict", values, whereClause, whereArgs);

               break;

          default:

               throw new IllegalArgumentException("unknown Uri:" + uri);

          }

          getContext().getContentResolver().notifyChange(uri, null);               return num;

          return num;

     }

}

---

系统CP

android对联系人管理ContentProvider的几个Uri如下

• ContactsContract.Contacts.CONTENT_URI
• ContactsContract.CommonDataKinds.Phone.CONTENT_URI
• ContactsContract.CommonDataKinds.Email.CONTENT_URI

Android为多媒体提供的ContentProvider的Uri如下：

MediaStore.Audio.Media.EXTERNAL_CONTENT_URI

MediaStore.Audio.Media.INTERNAL_CONTENT_URI

MediaStore.Images.Media.EXTERNAL_CONTENT_URI

MediaStore.Images.Media.INTERNAL_CONTENT_URI

MediaStore.Video.Media.EXTERNAL_CONTENT_URI

MediaStore.Video.Media.INTERNAL_CONTENT_URI

Android图片浏览器并不需要程序员去遍历SD卡的图片文件，直接查询系统多媒体ContentProvider即可获取系统中所有的图片信息