实施AsyncTask的最有效解决方案是什么。
我有一个工作应用，我的主要活动使用listView来显示数据库的结果。所有处理都在UI线程上执行。
但我当前的代码使用SQLiteDatabase和Cursor对象多种方法。最初填充listview时和使用CAB删除行时。
我到目前为止所做的尝试都失败了，因为我正在访问仍在UI线程上的对象。我不确定我应采取什么方法
以下是我的代码：
/** * A placeholder fragment containing a simple view. */
public static class PlaceholderFragment extends Fragment {
/** The fragment argument representing the section number for this fragment. */
private static final String ARG_SECTION_NUMBER = "section_number";
// TO and FROM arrays are used to map database columns to the corresponding elements on an XML layout file. The layout file is used by the adapter to populate the listView in the main fragment.
static final String[] FROM = { */Colums to query /*}; //end
static final int[] TO = { */destination colums /* }; // end
/** Returns a new instance of this fragment for the given section number. */
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
ListView layoutListView;
DatabaseHelper DbHelper;
SQLiteDatabase db;
Cursor cursor;
SimpleCursorAdapter adapter;
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// Find your views
layoutListView = (ListView) getView().findViewById(R.id.listView);
// Create a new helper to control db access and get a readable copy.
DbHelper = new DatabaseHelper(getActivity());
db = DbHelper.getReadableDatabase();
}
private void updateList(){
//requery and update cursor
querydb();
//tells the adapter the cursor/data has changed
adapter.notifyDataSetChanged();
}
private void querydb() {
//specify the columns to be used in the db query
String[] queryColumnList = { */ list of colums to query /* };
// Perform a db query and store a table of results in the cursor object
cursor = db.query(
DatabaseHelper.dBContract.TABLE_NAME, //table to be queried
queryColumnList, //The columns to return
null, //The column for the where clause
null, //The values for the where clause
null, //row grouping
null, //filter row groups
null //sort order
);
//find the layout that will be used for each item in the listview
int listItemLayoutID = R.layout.row;
//create a new adapter to deal with the implementation of building a listview
adapter = new SimpleCursorAdapter(getActivity(), listItemLayoutID, cursor, FROM, TO,2); //Arguments = context, layout for each row, From variable details data source, To variable details the id values of elements in the row layout file.
//show the adapter which listview it needs to populate
layoutListView.setAdapter(adapter);
}
}
}
到目前为止我尝试过：
private class getListData extends AsyncTask<Void, Void, Void> {
@Override // Do the long-running work in here
protected Void doInBackground(Void... Parms) {
final String[] FROM = { */ source list /*}; //end
final int[] TO = { */ destination list /* }; // end
//specify the columns to be used in the db query
String[] queryColumnList = {
dBHelper.dBContract.clutches._ID,
dBHelper.dBContract.clutches.C_NAME,
dBHelper.dBContract.clutches.C_EGG_COUNT,
dBHelper.dBContract.clutches.C_HATCH_START,
dBHelper.dBContract.clutches.C_HATCH_END,
};
// Perform a db query and store a table of results in the cursor object
cursor = db.query(
TABLE_NAME, //table to be queried
queryColumnList, //The columns to return
null, //The column for the where clause
null, //The values for the where clause
null, //row grouping
null, //filter row groups
null //sort order
);
}
// This is called each time you call publishProgress()
protected void onProgressUpdate() {
//setProgressPercent(progress[0]);
}
@Override // This is called when doInBackground() is finished
protected void onPostExecute(Void result) {
int listItemLayoutID = R.layout.row;
adapter = new SimpleCursorAdapter(getActivity(), listItemLayoutID, cursor, FROM, TO,2);
return null;
layoutListView.setAdapter(adapter);
}
}
编辑：LogCat
05-21 08：04：44.203 1639-1653 / co.uk.tickingClock.app E / AndroidRuntime：FATAL EXCEPTION：AsyncTask＃1 过程：co.uk.tickingClock.app，PID：1639 java.lang.RuntimeException：执行doInBackground（）时发生错误 在android.os.AsyncTask $ 3.done（AsyncTask.java:300） 在java.util.concurrent.FutureTask.finishCompletion（FutureTask.java:355） at java.util.concurrent.FutureTask.setException（FutureTask.java:222） 在java.util.concurrent.FutureTask.run（FutureTask.java:242） 在android.os.AsyncTask $ SerialExecutor $ 1.run（AsyncTask.java:231） at java.util.concurrent.ThreadPoolExecutor.runWorker（ThreadPoolExecutor.java:1112） at java.util.concurrent.ThreadPoolExecutor $ Worker.run（ThreadPoolExecutor.java:587） 在java.lang.Thread.run（Thread.java:841） 引起：java.lang.RuntimeException：无法在未调用Looper.prepare（）的线程内创建处理程序 在android.os.Handler。（Handler.java:200） 在android.os.Handler。（Handler.java:114） 在android.widget.CursorAdapter $ ChangeObserver。（CursorAdapter.java:453） 在android.widget.CursorAdapter.init（CursorAdapter.java:174） 在android.widget.CursorAdapter。（CursorAdapter.java:149） 在android.widget.ResourceCursorAdapter。（ResourceCursorAdapter.java:91） 在android.widget.SimpleCursorAdapter。（SimpleCursorAdapter.java:104） at co.uk.tickingClock.app.view_clutches $ PlaceholderFragment $ getListOfClutches.doInBackground（view_clutches.java:282） at co.uk.tickingClock.app.view_clutches $ PlaceholderFragment $ getListOfClutches.doInBackground（view_clutches.java:256） 在android.os.AsyncTask $ 2.call（AsyncTask.java:288） 在java.util.concurrent.FutureTask.run（FutureTask.java:237） 在android.os.AsyncTask $ SerialExecutor $ 1.run（AsyncTask.java:231） at java.util.concurrent.ThreadPoolExecutor.runWorker（ThreadPoolExecutor.java:1112） at java.util.concurrent.ThreadPoolExecutor $ Worker.run（ThreadPoolExecutor.java:587） 在java.lang.Thread.run（Thread.java:841）
答案 0 :(得分：1)
您正在初始化SimpleCursorAdapter中的doInBackground()。
在onPostExecute()。