http://blog.csdn.net/oney139/article/details/7932654
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, mySortOrder);
//Cursor ContentResolver Uri 之间的关系是什么
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
long rowId = db.insert(NOTES_TABLE_NAME, null, contentValues);
if(rowId > 0) {
Uri newUri = ContentUris.withAppendedId(NotePad.Notes.CONTENT_URI, rowId);
//这里的 ContentResolver.notifyChange(Uri,null)做了什么工作?
//和 Cursor.setNotificationUri()有什么关系
getContext().getContentResolver().notifyChange(newUri, null);
return newUri;
} else {
// android.database.SQLException
throw new SQLException("Failed to insert row into " + uri);
}
在实现 ContentProvider 的query 时,一般都有下面几行代码:
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, mySortOrder);
//这一行的代码的作用?
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
下面具体说下注释的那行的作用?
public void setNotificationUri(ContentResolver cr, Uri notifyUri) {
mContentResolver = cr;
mNotifyUri = notifyUri;
mSelfObserver = new SelfContentObserver(this);
//cr.registerContentObserver(notifyUri, mSelfObserver)
mContentResolver.registerContentObserver(mNotifyUri, true, mSelfObserver);
}
这个方法的作用就是在 ContentResolver上注册一个 Observer,
总体上的过程为:
//这个 Cursor 会被 Context.getContentResolver().query() 返回
Cursor c = SQLiteDatabase.query();
// 在 ContentResolver上注册一个 ContentObserver
c.setNotificationUri(ContentResolver,Uri)
//如果ContentObserver参数为null, 则ContentResolver会通知上一步注册的ContentObserver
getContentResolver().notifyChange(Uri,ContentObserver)
//Abstract Cursor 源码中的 setNotificationUri方法下的
new SelfContentObserver(this) //会获得ContentResolver发出的通知
SelfContentObserver会通知和其关联的Cursor(初始化SelfContentObserver时进行关联)
//在这个构造数内会设置 Cursor 的观察者为 CursorAdapter,具体可以查看源代码跟踪一下
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.notes_list_item,
c/* 指Cursor */, new String[]{NotePad.Notes.TITLE}, new int[]{R.id.text1});
另外Uri参数的用处没有搞太清楚,但总体上是:
content://com.example.notepad/notes/5 这种Uri也会引起 content://com.example.notepad/notes 这种Uri的改变
http://aijiawang-126-com.iteye.com/blog/812004
/**
* Receives notifications when the data in the content provider changes
*/
private class DownloadManagerContentObserver extends ContentObserver {
public DownloadManagerContentObserver() {
super(new Handler());
}
/**
* Receives notification when the data in the observed content
* provider changes.
*/
public void onChange(final boolean selfChange) {
if (Constants.LOGVV) {
Log.v(Constants.TAG, "Service ContentObserver received notification");
}
updateFromProvider();
}
}
public void onCreate() {
super.onCreate();
if (Constants.LOGVV) {
Log.v(Constants.TAG, "Service onCreate");
}
mDownloads = Lists.newArrayList();
mObserver = new DownloadManagerContentObserver();
getContentResolver().registerContentObserver(Downloads.CONTENT_URI,
true, mObserver);
......}
/**
* Cleans up when the service is destroyed
*/
public void onDestroy() {
getContentResolver().unregisterContentObserver(mObserver);
if (Constants.LOGVV) {
Log.v(Constants.TAG, "Service onDestroy");
}
super.onDestroy();
}