我正在开发用于显示大量RSS提要的Android应用程序(是的,我知道已经有很多这样的应用程序).内容提供者支持要显示的数据,我想与API级别4向后兼容.
我正在使用ExpandableListVIEw来显示三个不同的RSS Feed的内容. ExpandableListVIEw的适配器被实现为SimpleCursorTreeAdapter的子类:
private class RSSFeedLatestlistadapter extends SimpleCursorTreeAdapter { public static final String Feed_name_ColUMN = "Feedname"; public RSSFeedLatestlistadapter(Context ctx, Cursor groupCursor, int groupLayout, String[] groupFrom, int[] groupTo, int childLayout, String[] childFrom, int[] childTo) { super(ctx, groupCursor, groupLayout, groupLayout, groupFrom, groupTo, childLayout, childFrom, childTo); } @OverrIDe protected Cursor getChildrenCursor(final Cursor groupCursor) { final String Feedname = groupCursor.getString(groupCursor.getColumnIndex(Feed_name_ColUMN)); return managed@R_502_5962@(LATEST_URI, null, FeedItemColumns.category + " = ? AND " + FeedItemColumns.Feed + " = ?", new String[] { mcategory.getID(), Feedname }, null); } @OverrIDe protected voID bindGroupVIEw(VIEw vIEw, Context context, Cursor cursor, boolean isExpanded) { super.bindGroupVIEw(vIEw, context, cursor, isExpanded); // Bind group vIEw (impl details not important) ... } @OverrIDe protected voID bindChildVIEw(VIEw vIEw, Context context, Cursor cursor, boolean isLastChild) { super.bindChildVIEw(vIEw, context, cursor, isLastChild); // Bind child vIEw (impl details not important) ... }}
使用此设置,所有内容均按预期加载.但是,UI在列表内容加载期间随机挂起/结结.通常不足以获取ANR,但仍然很引人注目且非常烦人!
为了调试此问题,我启用了androID.os.StrictMode(很棒的新功能/工具btw!),并启动了模拟器(在AndroID 2.3上).加载列表内容时,将获得以下StrictMode输出:
D/StrictMode( 395): StrictMode policy violation; ~duration=1522 ms: androID.os.StrictMode$StrictModediskReadViolation: policy=23 violation=2D/StrictMode( 395): at androID.os.StrictMode$AndroIDBlockGuardPolicy.onReadFromdisk(StrictMode.java:745)D/StrictMode( 395): at androID.database.sqlite.sqliteDatabase.raw@R_502_5962@WithFactory(sqliteDatabase.java:1345)D/StrictMode( 395): at androID.database.sqlite.sqlite@R_502_5962@Builder.@R_502_5962@(sqlite@[email protected]:330)D/StrictMode( 395): at com.mycompany.myapp.provIDer.RSSFeedProvIDer.@R_502_5962@(RSSFeedProvIDer.java:128)D/StrictMode( 395): at androID.content.ContentProvIDer$Transport.@R_502_5962@(ContentProvIDer.java:187)D/StrictMode( 395): at androID.content.ContentResolver.@R_502_5962@(ContentResolver.java:262)D/StrictMode( 395): at androID.app.Activity.managed@R_502_5962@(Activity.java:1550)D/StrictMode( 395): at com.mycompany.myapp.activity.MultipleFeedsActivity$RSSFeedLatestlistadapter.getChildrenCursor(MultipleFeedsActivity.java:388)D/StrictMode( 395): at androID.Widget.CursorTreeAdapter.getChildrenCursorHelper(CursorTreeAdapter.java:106)D/StrictMode( 395): at androID.Widget.CursorTreeAdapter.getChildrenCount(CursorTreeAdapter.java:178)D/StrictMode( 395): at androID.Widget.ExpandableListConnector.refreshExpGroupMetadataList(ExpandableListConnector.java:561)D/StrictMode( 395): at androID.Widget.ExpandableListConnector.expandGroup(ExpandableListConnector.java:682)D/StrictMode( 395): at androID.Widget.ExpandableListConnector.expandGroup(ExpandableListConnector.java:636)D/StrictMode( 395): at androID.Widget.ExpandableListVIEw.expandGroup(ExpandableListVIEw.java:608)D/StrictMode( 395): at com.mycompany.myapp.activity.MultipleFeedsActivity.onReceiveResult(MultipleFeedsActivity.java:335)D/StrictMode( 395): at com.mycompany.myapp.service.FeedResultReceiver.onReceiveResult(FeedResultReceiver.java:40)D/StrictMode( 395): at androID.os.ResultReceiver$MyRunnable.run(ResultReceiver.java:43)D/StrictMode( 395): at androID.os.Handler.handleCallback(Handler.java:587)D/StrictMode( 395): at androID.os.Handler.dispatchMessage(Handler.java:92)D/StrictMode( 395): at androID.os.Looper.loop(Looper.java:123)D/StrictMode( 395): at androID.app.ActivityThread.main(ActivityThread.java:3647)D/StrictMode( 395): at java.lang.reflect.Method.invokeNative(Native Method)D/StrictMode( 395): at java.lang.reflect.Method.invoke(Method.java:507)D/StrictMode( 395): at com.androID.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)D/StrictMode( 395): at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:597)D/StrictMode( 395): at dalvik.system.NativeStart.main(Native Method)
这似乎是合理的!在SimpleCursorTreeAdapter.getChildrenCursor()中,将在UI线程上查询内容提供者,这当然是一个坏主意,它肯定会挂断UI!
我看了一下CursorTreeAdapter(SimpleCursorTreeAdapter的超类)的JavaDoc(API级别4),对于getChildrenCursor()它说:
“如果要异步查询提供程序以防止阻塞UI,则可以返回null,并在以后调用setChildrenCursor(int,Cursor).”
大!让我们开始吧!我更改了getChildrenCursor()的实现,以启动一个新任务,该任务负责执行查询并在适配器上设置子级光标.开始任务后,我只是在getChildrenCursor()中返回null:
@OverrIDeprotected Cursor getChildrenCursor(final Cursor groupCursor) { final String Feedname = groupCursor.getString(groupCursor.getColumnIndex(Feed_name_ColUMN)); new RefreshChildrenCursorTask(groupCursor.getposition()).execute(Feedname); return null;}
,其中RefreshChildrenCursorTask实现为:
private class RefreshChildrenCursorTask extends AsyncTask<String, VoID, Cursor> { private int mGroupposition; public RefreshChildrenCursorTask(int groupposition) { this.mGroupposition = groupposition; } @OverrIDe protected Cursor doInBackground(String... params) { String Feedname = params[0]; return managed@R_502_5962@(LATEST_URI, null, FeedItemColumns.category + " = ? AND " + FeedItemColumns.Feed + " = ?", new String[] { mcategory.getID(), Feedname }, null); } @OverrIDe protected voID onPostExecute(Cursor childrenCursor) { mLatestlistadapter.setChildrenCursor(mGroupposition, childrenCursor); } }}
我在2.3模拟器上重新安装了该应用程序并启动了它.它像魅力一样,再见了无响应的用户界面!但是这种欢乐并没有持续很长时间……接下来要做的是在目标设备上运行相同的代码(在本例中为运行AndroID 2.2的三星galaxy S).然后,我在加载列表供稿内容期间遇到了以下异常:
E/AndroIDRuntime(23191): FATAL EXCEPTION: mainE/AndroIDRuntime(23191): java.lang.NullPointerExceptionE/AndroIDRuntime(23191): at androID.Widget.SimpleCursorTreeAdapter.initFromColumns(SimpleCursorTreeAdapter.java:194)E/AndroIDRuntime(23191): at androID.Widget.SimpleCursorTreeAdapter.initChildrenFromColumns(SimpleCursorTreeAdapter.java:205)E/AndroIDRuntime(23191): at androID.Widget.SimpleCursorTreeAdapter.init(SimpleCursorTreeAdapter.java:186)E/AndroIDRuntime(23191): at androID.Widget.SimpleCursorTreeAdapter.(SimpleCursorTreeAdapter.java:136)E/AndroIDRuntime(23191): at com.mycompany.myapp.activity.MultipleFeedsActivity$RSSFeedLatestlistadapter.(MultipleFeedsActivity.java:378)E/AndroIDRuntime(23191): at com.mycompany.myapp.activity.MultipleFeedsActivity.run(MultipleFeedsActivity.java:150)E/AndroIDRuntime(23191): at androID.os.Handler.handleCallback(Handler.java:587)E/AndroIDRuntime(23191): at androID.os.Handler.dispatchMessage(Handler.java:92)E/AndroIDRuntime(23191): at androID.os.Looper.loop(Looper.java:123)E/AndroIDRuntime(23191): at androID.app.ActivityThread.main(ActivityThread.java:4627)E/AndroIDRuntime(23191): at java.lang.reflect.Method.invokeNative(Native Method)E/AndroIDRuntime(23191): at java.lang.reflect.Method.invoke(Method.java:521)E/AndroIDRuntime(23191): at com.androID.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:871)E/AndroIDRuntime(23191): at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:629)E/AndroIDRuntime(23191): at dalvik.system.NativeStart.main(Native Method)
快速浏览一下SimpleCursorTreeAdapter的源代码可知,它无法应付从getChildrenCursor()异步返回的null.他们似乎已经在AndroID 2.3中解决了这个问题,但是您应该如何在AndroID的早期版本中解决它呢?我是否真的必须编写自己的CursorTreeAdapter实现才能异步刷新子游标?
是否有人遇到过同样的问题,甚至找到了(可行的)解决方法?如果没有,有人可以提示我如何进行!!我会很感激我能得到的任何帮助!
提前致谢!
问候,
雅各布
解决方法:
如果他们在2.3 SimpleCursorTreeAdapter中进行了修复,为什么不下载Java文件并将其包含在项目中并使用该版本而不是电话上的版本呢?
我没有看过代码,但是只要他们没有进行任何新的2.3 API调用,它就应该起作用.
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