Android四大组件之ContentProvider

Android四大组件之一Contentprovider的两大功能

1.进程间通信

2.数据有变化及时通知使用者

这篇文章讲解数据变化时通知使用者的功能，对于及时需要知道数据变化的场景有很大帮助。

文件下载过程， 使用该监听很好实现对ListView列表进行刷新。

这里贴出来刷新UI相关的代码，下载模块，自己实现就ok了，只要数据表中的数据发生变化，就会回调ContentObserver的onChange(...)方法。

初始化BaseAdapter时,注册监听数据表变化的观察者。

public class ListDownloadDocHandler extends BaseAdapter {
private DownloadObserver localObserver;

private ListDownloadDocHandler listDownloadDocHandler;

public ListDocDownloadAdapter(Context context) {
localObserver = new DownloadObserver(null, listNonDownloadDocHandler);
//注册数据观察者
mContext.getContentResolver().registerContentObserver(ICorporateDocDao.COLUMNS.CONTENT_URI,
true, localObserver);
}
/**
*文档全部下载完，取消数据观察者
*
*/
public void unregisterContentObserver() {
mContext.getContentResolver().unregisterContentObserver(localObserver);
}
static class ListDownloadDocHandler extends Handler {
WeakReference<ListDocDownloadAdapter> listDocAdapter;
ListDocDownloadAdapter locallistDocAdapter;

public ListNonDownloadDocHandler(ListDocNondownloadAdapter listDocAdapter) {
this.listDocAdapter = new WeakReference<ListDocDownloadAdapter>(listDocAdapter);
}

...
...

public void handleMessage(Message msg) {
if (listDocAdapter == null) {
Logger.d(loggerName, "listDocAdapter is null");
return;
}
locallistDocAdapter = listDocAdapter.get();
switch (msg.what) {
case DownloadKeys.DOWNLOADING_TASK:
locallistDocAdapter.uiRefresh();
break;
default:
break;
}
}
}
/**
* 实现子类DownloadObserver继承 ContentObserver接口
*
*/class DownloadObserver extends ContentObserver {
private Handler handler;

public DownloadObserver(Uri mediaUri, Handler paramHandler) {
super(paramHandler);
handler = paramHandler;
}

/**
*ICorporateDocDao.COLUMNS.CONTENT_URI数据变化时，回调onChange(...)
*/
@Override
public void onChange(boolean paramBoolean) {
super.onChange(paramBoolean);
if (dataList == null || dataList.isEmpty()) {
Logger.d(loggerName, "dataList is null");
return;
}
handler.sendEmptyMessage(DownloadKeys.DOWNLOADING_TASK);
}
}

public class CorporateDocProvider extends ContentProvider {
private final String TAG = "CorporateDocProvider";

private static final UriMatcher URI_MATCHER = new UriMatcher(UriMatcher.NO_MATCH);

private static final int MEDIA = 1000;

private static final int MEDIA_ID = 1001;

static {
URI_MATCHER.addURI("com.demo.emm", "media_doc", 1000);
URI_MATCHER.addURI("com.demo.emm", "media_doc/#", 1001);
}

@Override
public boolean onCreate() {
return false;
}

@Override
public Cursor query(Uri paramUri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder localSQLiteQueryBuilder = new SQLiteQueryBuilder();
int i = URI_MATCHER.match(paramUri);
switch (i) {
case MEDIA:
localSQLiteQueryBuilder.setTables("media_doc");
break;
case MEDIA_ID:
localSQLiteQueryBuilder.setTables("media_doc");
localSQLiteQueryBuilder.appendWhere("content_id = "
+ (String)paramUri.getPathSegments().get(1));
break;

default:
break;
}
Cursor localCursor = localSQLiteQueryBuilder.query(
MDMDatabaseUtils.getInstance(getContext()).openDatabase(), projection, selection,
selectionArgs, null, null, sortOrder);
if (localCursor != null) {
localCursor.setNotificationUri(getContext().getContentResolver(), paramUri);
} else {
Logger.d(TAG, "localCursor == null");
}
return localCursor;
}

@Override
public String getType(Uri uri) {
return null;
}

@Override
public Uri insert(Uri paramUri, ContentValues values) {
SQLiteDatabase localSQLiteDatabase = MDMDatabaseUtils.getInstance(getContext())
.openDatabase();
Uri localUri = null;
int i = URI_MATCHER.match(paramUri);
try {
localSQLiteDatabase.beginTransaction();
switch (i) {
case MEDIA:
case MEDIA_ID:
long l1 = localSQLiteDatabase.insert("media_doc", null, ensureFile(values));
if (l1 > 0) {
localSQLiteDatabase.setTransactionSuccessful();
} else {
Logger.d(TAG, "insert media_doc data failure" + values.toString());
}
if (paramUri != null) {
getContext().getContentResolver().notifyChange(paramUri, null);
localUri = paramUri;
}
break;
default:
throw new UnsupportedOperationException("Invalid URI " + paramUri);
}

} catch (Exception e) {
Logger.d(TAG, e.getMessage());
} finally {
if (null != localSQLiteDatabase) {
localSQLiteDatabase.endTransaction();
}
}

return localUri;
}

@Override
public int delete(Uri paramUri, String whereClause, String[] whereArgs) {
SQLiteDatabase localSQLiteDatabase = MDMDatabaseUtils.getInstance(getContext())
.openDatabase();
int flag = 0;
int i = URI_MATCHER.match(paramUri);
try {
localSQLiteDatabase.beginTransaction();
switch (i) {
case MEDIA_ID:
String id = (String)paramUri.getPathSegments().get(1);
if (!TextUtils.isEmpty(id)) {
String str3 = COLUMNS.CONTENT_ID + " = "
+ (String)paramUri.getPathSegments().get(1);
if (whereClause == null) {
whereClause = str3;
} else {
whereClause = str3 + " AND (" + whereClause + ")";
}
}
int l1 = localSQLiteDatabase.delete("media_doc", whereClause, whereArgs);

if (l1 > 0) {
localSQLiteDatabase.setTransactionSuccessful();
} else {
Logger.d(TAG, "media_doc delete fail=" + whereClause + "="
+ whereArgs.length);
}
if (paramUri != null)
getContext().getContentResolver().notifyChange(paramUri, null);
break;
case MEDIA:
int l2 = localSQLiteDatabase.delete("media_doc", whereClause, whereArgs);
if (l2 > 0) {
localSQLiteDatabase.setTransactionSuccessful();
} else {
Logger.d(TAG, "media_doc delete fail=" + whereClause + "="
+ whereArgs.length);
}
if (paramUri != null)
getContext().getContentResolver().notifyChange(paramUri, null);
break;

default:
break;
}

} catch (Exception e) {
Logger.d(TAG, e.getMessage());
} finally {
if (null != localSQLiteDatabase) {
localSQLiteDatabase.endTransaction();
}
}
return flag;
}

@Override
public int update(Uri paramUri, ContentValues values, String selection, String[] selectionArgs) {
SQLiteDatabase localSQLiteDatabase = MDMDatabaseUtils.getInstance(getContext())
.openDatabase();
int i = URI_MATCHER.match(paramUri);
localSQLiteDatabase.beginTransaction();
int index = -1;
Uri localUri = null;
try {
switch (i) {
case MEDIA:
case MEDIA_ID:
int l1 = localSQLiteDatabase.update("media_doc", values, selection,
selectionArgs);
if (l1 > 0) {
localSQLiteDatabase.setTransactionSuccessful();
} else {
Logger.d(TAG, "update fail=" + values);
}
if (paramUri != null)
getContext().getContentResolver().notifyChange(paramUri, null);
break;

default:
break;
}

} catch (Exception e) {
Logger.d(TAG, e.getMessage());
} finally {
if (null != localSQLiteDatabase) {
localSQLiteDatabase.endTransaction();
}
}
return index;
}

private ContentValues ensureFile(ContentValues paramContentValues) {
return paramContentValues;
}
}

AndroidManifest.xml配置文件中设置：

<provider
android:name="com.polysaas.mdm.dao.impl.CorporateDocProvider"
android:authorities="com.demo.emm" >
</provider>