使用SQLite的Android ListView
我试图在片段类中填充listview。我试图质疑的是,每一个学生都有很多要做的事情。当用户登录时,我想检索他唯一添加的所有ToDo,并且只显示属于他的数据 这是我的notes控件,用于检索所有notes使用SQLite的Android ListView,android,android-fragments,android-listview,android-sqlite,Android,Android Fragments,Android Listview,Android Sqlite,我试图在片段类中填充listview。我试图质疑的是,每一个学生都有很多要做的事情。当用户登录时,我想检索他唯一添加的所有ToDo,并且只显示属于他的数据 这是我的notes控件,用于检索所有notes private DatabaseHelper help; private SQLiteDatabase db; public Cursor listNotes() { Cursor c = db.query(help.NOTE_TABLE, new String[]{h
private DatabaseHelper help;
private SQLiteDatabase db;
public Cursor listNotes() {
Cursor c = db.query(help.NOTE_TABLE, new String[]{help.COLUMN_TITLE,help.COLUMN_BODY, help.COLUMN_DATE}, help.COLUMN_ID + " = ?", new String[]{String.valueOf(help.NOTES_ID)} , null, null, null);
if(c != null) {
c.moveToFirst();
}
return c;
}
我的databasehelper是只创建表的类。为什么当我试图获取数据时它是一个空指针,这是我的populateList方法
public void populateList(){
Cursor cursor = execute.listNotes();
//Mapping the fields cursor to text views
String[] fields = new String[]{help.COLUMN_TITLE,help.COLUMN_BODY, help.COLUMN_DATE};
int [] text = new int[] {R.id.item_title,R.id.item_body, R.id.item_date};
adapter = new SimpleCursorAdapter(getActivity(),R.layout.list_layout,cursor, fields, text,0);
//Calling list object instance
listView = (ListView) getView().findViewById(android.R.id.list);
listView.setAdapter(adapter);
}
LogCat
java.lang.NullPointerException
at com.example.app.Notes.populateList(Notes.java:49)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
at android.support.v4.view.ViewPager$3.run(ViewPager.java:249)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
at android.view.Choreographer.doCallbacks(Choreographer.java:555)
at android.view.Choreographer.doFrame(Choreographer.java:524)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
在访问任何数据之前,您将关闭光标。您需要将要查找的数据放入对象中,然后返回该对象。不要返回光标
public MyObject listNotes() {
Cursor c = db.query("YOUR_QUERY");
MyObject obj = new MyObject();
if (c != null && c.moveToFirst()) {
obj.setParameter(c.getInt(c.getColumnIndex("column_name")));
}
c.close();
return obj;
}
当然,这是假设光标的第一个元素是您要查找的项目。您对
列表注释
函数的引用有错误execute
没有名为listNotes的函数,因此返回的是null
您需要引用listNotes出现的实际类,例如
Controls.listNotes()代码>请发布完整的adb日志跟踪。为什么在返回c
之前调用c.close()
?如果关闭光标
,它将不再可用(也可能被设置为null
)。我已删除了c.close(),仍然没有将光标传递到我的填充列表不会,而(c!=null)
会创建一个无限循环吗?@yuttadhammo会吗,我如何将光标传递到我的列表视图?