我一直在尝试使用AsyncTask从sqlite表中检索数据的应用程序。它偶尔可以在没有太多问题的情况下工作。但是当它失败时,Logcat看起来像这样
07-24 16:06:20.477:E / AndroidRuntime(950):致命异常:AsyncTask#1
07-24 16:06:20.477:E / AndroidRuntime(950):java.lang.RuntimeException:执行doInBackground()时发生错误
07-24 16:06:20.477:E / AndroidRuntime(950):在android.os.AsyncTask $ 3.done(AsyncTask.java:278)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.FutureTask $ Sync.innerSetException(FutureTask.java:273)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.FutureTask $ Sync.innerRun(FutureTask.java:307)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-24 16:06:20.477:E / AndroidRuntime(950):在android.os.AsyncTask $ SerialExecutor $ 1.run(AsyncTask.java:208)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.ThreadPoolExecutor $ Worker.run(ThreadPoolExecutor.java:569)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.lang.Thread.run(Thread.java:856)
07-24 16:06:20.477:E / AndroidRuntime(950):引起:java.lang.NullPointerException
07-24 16:06:20.477:E / AndroidRuntime(950):在com.brionsoftwares.android.pilgrimhelper.test.PilgrimDao.getPilgrim(PilgrimDao.java:21)
07-24 16:06:20.477:E / AndroidRuntime(950):在com.brionsoftwares.android.pilgrimhelper.PilgrimSearchActivity $ DataQuery.doInBackground(PilgrimSearchActivity.java:45)
07-24 16:06:20.477:E / AndroidRuntime(950):在com.brionsoftwares.android.pilgrimhelper.PilgrimSearchActivity $ DataQuery.doInBackground(PilgrimSearchActivity.java:1)
07-24 16:06:20.477:E / AndroidRuntime(950):在android.os.AsyncTask $ 2.call(AsyncTask.java:264)
07-24 16:06:20.477:E / AndroidRuntime(950):at java.util.concurrent.FutureTask $ Sync.innerRun(FutureTask.java:305)
07-24 16:06:20.477:E / AndroidRuntime(950):... 5更多
的AsyncTask
protected Void doInBackground(String... params) {
List<Pilgrim> pilgrimList=PilgrimDao.getPilgrim(pilgrimDatabase.getSqlLiteDatabase(), params);
ArrayList<Map<String, String>> list = buildData(pilgrimList);
String[] from={"Name","District"};
int[] to={android.R.id.text1, android.R.id.text2};
simpleAdapter= new SimpleAdapter(getApplicationContext(), list, R.layout.simple_list_item_2, from, to);
return null;
}
@Override
protected void onPostExecute(Void result) {
mProgressBar.setVisibility(View.GONE);
mListView.setAdapter(simpleAdapter);
mListView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
Toast.makeText(PilgrimSearchActivity.this, "Select", Toast.LENGTH_LONG).show();
}
});
super.onPostExecute(result);
}
}
PilgrimDao.getPilgrim方法
public static List<Pilgrim> getPilgrim(SQLiteDatabase database, String[] params) {
List<Pilgrim> shippers = new LinkedList<Pilgrim>();
String selection="Name = ?";
Cursor cursor = database.query(TABLE, COLUMNS, selection, params, null,null, null); //line 21
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
Pilgrim pilgrim= new Pilgrim();
pilgrim.setName(cursor.getString(0));
pilgrim.setDistrict(cursor.getString(1));
shippers.add(pilgrim);
cursor.moveToNext();
}
cursor.close();
Log.v(PilgrimSearchActivity.TAG,"PilgrimDao returning " + shippers.size() + " shippers");
return shippers;
}
为什么线程退出?我可以做些什么改变来使这段代码顺利运行?
答案 0 :(得分:2)
正如您在注释中看到的那样,您将获得空指针异常,可能是您传递的URI错误,或者任何参数,请确保正确。试试这个:
public static List<Pilgrim> getPilgrim(SQLiteDatabase database, String[] params) {
List<Pilgrim> shippers = new LinkedList<Pilgrim>();
String selection="Name = ?";
try{
Cursor cursor = database.query(TABLE, COLUMNS, selection, params, null,null,null); //line 21
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
Pilgrim pilgrim= new Pilgrim();
pilgrim.setName(cursor.getString(0));
pilgrim.setDistrict(cursor.getString(1));
shippers.add(pilgrim);
cursor.moveToNext();
}
}catch (Exception e)
{
e.printStackTrace();//this will print in your logcat any possible exception.
}
cursor.close();
Log.v(PilgrimSearchActivity.TAG,"PilgrimDao returning " + shippers.size() + " shippers");
return shippers;
};