我的android 第21天 - ?使用ContentProvider共享数据
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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。以前我们学习过文件的操作模式，通过指定文件的操作模式为Context.MODE_WORLD_READABLE 或Context.MODE_WORLD_WRITEABLE同样可以对外共享数据，但数据的访问方式会因数据存储的方式而不同，如：采用xml文件对外共享数据，需要进行xml解析来读写数据；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。
当应用需要通过ContentProvider对外共享数据时，第一步需要继承ContentProvider并重写下面方法：
publicclass?PersonContentProviderextends?ContentProvider{
?? public?booleanonCreate()
?? public Uri insert(Uri?uri,?ContentValuesvalues)
?? public?intdelete(Uri?uri,String selection, String[]?selectionArgs)
?? public?intupdate(Uri?uri,?ContentValuesvalues, String selection, String[]?selectionArgs)
?? public Cursor query(Uri?uri,String[] projection, String selection, String[]?selectionArgs,String?sortOrder)
?? public String?getType(Uriuri)}
第二步需要在AndroidManifest.xml使用<provider>对该ContentProvider进行配置，为了能让其他应用找到该ContentProvider ， ContentProvider 采用了authorities（主机名/域名）对它进行唯一标识，你可以把 ContentProvider看作是一个网站（想想，网站也是提供数据者），authorities 就是他的域名：
<manifest .... >
???<application android:icon="@drawable/icon" android:label="@string/app_name">
????????<provider?android:name=".PersonContentProvider"?android:authorities="cn.itcast.providers.personprovider"/>
???</application>
</manifest>
注意：一旦应用继承了ContentProvider类，后面我们就会把这个应用称为ContentProvider（内容提供者）。
package cn.itcast.db;import cn.itcast.service.DBOpenHelper;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 PersonContentProvider extends ContentProvider { private static UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH); private static final int PERSONS = 1; private static final int PERSON = 2; private DBOpenHelper dbOpenHelper; static{ matcher.addURI("cn.itcast.providers.personprovider", "person", PERSONS); matcher.addURI("cn.itcast.providers.personprovider", "person/#", PERSON); } @Override public boolean onCreate() { dbOpenHelper = new DBOpenHelper(this.getContext()); return true; } @Override public int delete(Uri uri, String selection, String[] selectionArgs) { SQLiteDatabase db = dbOpenHelper.getWritableDatabase(); int num = 0 ;//已经删除的记录数量 switch (matcher.match(uri)) { case PERSONS: num = db.delete("person", selection, selectionArgs); break; case PERSON: long id = ContentUris.parseId(uri); String where = "personid="+ id; if(selection!=null && !"".equals(selection)){ // personid=12 and name=? where = where + " and "+ selection; } num = db.delete("person", where, selectionArgs); break; default: throw new IllegalArgumentException("Unkown Uri:"+ uri); } getContext().getContentResolver().notifyChange(uri, null); return num; } @Override public String getType(Uri uri) {//返回当前操作的数据类型 switch (matcher.match(uri)) { case PERSONS://操作的是集合类型数据 return "vnd.android.cursor.dir/person"; case PERSON: return "vnd.android.cursor.item/person"; default: throw new IllegalArgumentException("Unkown Uri:"+ uri); } } @Override public Uri insert(Uri uri, ContentValues values) { SQLiteDatabase db = dbOpenHelper.getWritableDatabase(); long id = 0 ; switch (matcher.match(uri)) { case PERSONS: id = db.insert("person", "personid", values);//得到记录的id getContext().getContentResolver().notifyChange(uri, null); return ContentUris.withAppendedId(uri, id);//返回代表新增记录的Uri case PERSON: id = db.insert("person", "personid", values);//得到记录的id String strUri = uri.toString(); Uri personUri = Uri.parse(strUri.substring(0, strUri.lastIndexOf("/"))); getContext().getContentResolver().notifyChange(personUri, null); return ContentUris.withAppendedId(personUri, id); default: throw new IllegalArgumentException("Unkown Uri:"+ uri); } } @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteDatabase db = dbOpenHelper.getReadableDatabase(); switch (matcher.match(uri)) { case PERSONS: return db.query("person", projection, selection, selectionArgs, null, null, sortOrder); case PERSON: long id = ContentUris.parseId(uri); String where = "personid="+ id; if(selection!=null && !"".equals(selection)){ // personid=12 and name=? where = where + " and "+ selection; } return db.query("person", projection, where, selectionArgs, null, null, sortOrder); default: throw new IllegalArgumentException("Unkown Uri:"+ uri); } } @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { SQLiteDatabase db = dbOpenHelper.getWritableDatabase(); int num = 0 ;//已经修改的记录数量 switch (matcher.match(uri)) { case PERSONS: num = db.update("person", values, selection, selectionArgs); break; case PERSON: long id = ContentUris.parseId(uri); String where = "personid="+ id; if(selection!=null && !"".equals(selection)){ where = where + " and "+ selection; } num = db.update("person", values, where, selectionArgs); break; default: throw new IllegalArgumentException("Unkown Uri:"+ uri); } getContext().getContentResolver().notifyChange(uri, null);//通知数据发生变化 return num; }}?
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