这是我从 getbeat 方法调用 getquery 结果的代码，但我总是收到错误，因为"尝试在空对象引用上调用虚拟方法'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery（java.lang.String， java.lang.String[]）'
public class report extends Fragment {
private ImageButton BtnImgCal;
private Spinner spinbt;
private Spinner spindr;
private Calendar cal;
private FragmentActivity myContext;
Button btnsun;
int day;
int month;
int year;
private EditText et;
static final int DATE_PICKER_ID = 1111;
private int Year;
private int Month ;
private int Day ;
String[] MonthNames = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
GetLocation loc;
double lati,longi;
DBAdapter db;
String[] beat;
String[] Beat;
public report(){}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState)
{
String[] strtext = getArguments().getStringArray("beatarray");
beat=strtext.clone();
View rootView = inflater.inflate(R.layout.call_report, container, false);
return rootView;
}
@Override
public void onViewCreated(final View view,Bundle savedInstanceState)
{
super.onViewCreated(view, savedInstanceState);
db=new DBAdapter(getActivity());
GetBeat();
}
BtnImgCal = (ImageButton) getActivity().findViewById(R.id.ImgCalBtn);
cal = Calendar.getInstance();
day = cal.get(Calendar.DAY_OF_MONTH);
month = cal.get(Calendar.MONTH);
year = cal.get(Calendar.YEAR);
et = (EditText) getActivity().findViewById(R.id.etdate);
et.setText(day+"-"+ MonthNames[month] +"-"+year);
spinbt=(Spinner) this.getActivity().findViewById(R.id.spinBeat);
spinbt.setPrompt("Select Beat");
btnsun = (Button)this.getActivity().findViewById(R.id.btn_submit);
final ToggleButton toggleButton = (ToggleButton) getActivity().findViewById(R.id.tglbtn);
toggleButton.setOnCheckedChangeListener(new OnCheckedChangeListener()
BtnImgCal.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
//Toast.makeText(getActivity(),"Daily Call Summary",Toast.LENGTH_SHORT).show();
DialogFragment newFragment = new SelectDateFragment();
newFragment.show(getFragmentManager(), "DatePicker");
}
});
}
private void GetBeat() {
Cursor gb=db.getQueryResult("Select beatid,beat_name from beat_mas");
if(gb.getCount()>0)
{
Beat = new String[gb.getCount()+1];
int i=0;
Beat[0]="Select Beat";
if (gb.moveToFirst())
{
if (gb.moveToFirst())
{
do
{
Beat[i+1] =gb.getString(1) + " :ID-" + gb.getInt(0); //Town Id
i+=1;
} while (gb.moveToNext());
}
gb.close(); //close db
}
}
}
我的DBAdapter是
public class DBAdapter
{
public static final String KEY_ROWID = "_id"; //Table Fields ....
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "bioderma"; //Database Name
private static final int DATABASE_VERSION =41;
public static String DateTime = null;
private static final String DATABASE_CREATE_app_req =
"create table app_req (_id integer primary key autoincrement, "
+ "req_no integer not null);";
//Login Master
private static final String DATABASE_CREATE_login_mas =
"create table login_mas (_id integer primary key autoincrement, userid integer not null, name text not null, "
+ "login_id text not null, password text not null, auth_key text not null, login_flag integer not null, "
+ "port_day integer null , port_month integer null, port_year integer null, "
+ "user_type integer not null,sms_mode integer not null,dc_type integer not null);";
//Beat Master
private static final String DATABASE_CREATE_beat_mas =
"create table beat_mas (_id integer primary key autoincrement, beatid integer not null, "
+ "beat_name text not null);";
//import log
private static final String DATABASE_CREATE_import_log =
"create table import_log (_id integer primary key autoincrement, "
+ "port_flag integer not null);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
System.out.println("this.context>>>>>>>>>>>>>>>>>"+ this.context);
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(DATABASE_CREATE_app_req);
db.execSQL(DATABASE_CREATE_login_mas);
db.execSQL(DATABASE_CREATE_beat_mas);
db.execSQL(DATABASE_CREATE_import_log);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS app_req");
db.execSQL("DROP TABLE IF EXISTS login_mas");
db.execSQL("DROP TABLE IF EXISTS beat_mas");
db.execSQL("DROP TABLE IF EXISTS import_log");
onCreate(db);
}
}
//-------------------------- Insert ------------------------------------------------------------------------------
public long insertBeat(int beatid, String beat_name)
{
ContentValues initialValues = new ContentValues();
initialValues.put("beatid", beatid);
initialValues.put("beat_name", beat_name);
return db.insert("beat_mas", null, initialValues);
}
public long insertimport(int imp_log)
{
ContentValues initialValues = new ContentValues();
initialValues.put("port_flag", imp_log);
return db.insert("import_log", null, initialValues);
}
//-------------------------- Insert Ends Here------------------------------------------------------------------------------
//-------------------------- Update ------------------------------------------------------------------------------
//executing query and it returns fields which are specified in the query ..........
public Cursor getQueryResult(String MY_QUERY) throws SQLException
{
try {
return db.rawQuery(MY_QUERY, null);
} catch (Exception e) {
System.out.println("getQueryResult error>>>>>>>>>>>>> :" + e.toString());
}
return null;
}
}
我只有在处理片段时才会遇到这个问题......
注意。。。我在我的应用程序中使用Hamburger_menu....我有片段 A，B，C，D所有片段都是 MainActivity 的子片段。在主活动中，我可以执行 sqlite 操作，但在片段中我收到错误为"尝试在空对象引用上调用虚拟方法'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery（java.lang.String， java.lang.String[]）'
"这是我的日志
02-03 12:56:43.482: I/art(17996): Debugger is active
02-03 12:56:43.672: I/System.out(17996): Debugger has connected
02-03 12:56:43.672: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:43.872: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:44.073: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:44.276: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:44.476: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:44.676: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:44.876: I/System.out(17996): waiting for debugger to settle...
02-03 12:56:45.077: I/System.out(17996): debugger has settled (1462)
02-03 12:56:45.123: V/Monotype(17996): SetAppTypeFace- try to flip, app = com.example.bioderma
02-03 12:56:45.131: V/Monotype(17996): Typeface getFontPathFlipFont - systemFont = default#default
02-03 12:56:45.149: I/System.out(17996): this.context>>>>>>>>>>>>>>>>>com.example.bioderma.Login@3d712f6f
02-03 12:56:45.160: V/Monotype(17996): SetAppTypeFace- try to flip, app = com.example.bioderma
02-03 12:56:45.160: V/Monotype(17996): Typeface getFontPathFlipFont - systemFont = default#default
02-03 12:56:48.119: I/System.out(17996): intent>>>>>>>>Intent { cmp=com.example.bioderma/.MainActivity }
02-03 12:56:48.140: I/System.out(17996): this.context>>>>>>>>>>>>>>>>>com.example.bioderma.MainActivity@181d2119
02-03 12:56:48.143: V/Monotype(17996): SetAppTypeFace- try to flip, app = com.example.bioderma
02-03 12:56:48.143: V/Monotype(17996): Typeface getFontPathFlipFont - systemFont = default#default
02-03 12:56:48.876: I/System.out(17996): activity>>>>>>>>>>>>>>>>>android.app.Application@1a9dd12a
02-03 12:56:49.392: D/Network(17996): Network
02-03 12:56:49.392: I/System.out(17996): this.context>>>>>>>>>>>>>>>>>com.example.bioderma.MainActivity@181d2119
02-03 12:56:49.759: I/System.out(17996): getQueryResult error>>>>>>>>>>>>> :java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference
02-03 12:56:55.398: D/AndroidRuntime(17996): Shutting down VM
02-03 12:56:55.402: E/AndroidRuntime(17996): FATAL EXCEPTION: main
02-03 12:56:55.402: E/AndroidRuntime(17996): Process: com.example.bioderma, PID: 17996
02-03 12:56:55.402: E/AndroidRuntime(17996): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bioderma/com.example.bioderma.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2316)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2376)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread.access$800(ActivityThread.java:147)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1281)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.os.Handler.dispatchMessage(Handler.java:102)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.os.Looper.loop(Looper.java:135)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread.main(ActivityThread.java:5253)
02-03 12:56:55.402: E/AndroidRuntime(17996): at java.lang.reflect.Method.invoke(Native Method)
02-03 12:56:55.402: E/AndroidRuntime(17996): at java.lang.reflect.Method.invoke(Method.java:372)
02-03 12:56:55.402: E/AndroidRuntime(17996): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900)
02-03 12:56:55.402: E/AndroidRuntime(17996): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:695)
02-03 12:56:55.402: E/AndroidRuntime(17996): Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference
02-03 12:56:55.402: E/AndroidRuntime(17996): at com.example.bioderma.report.GetBeat(report.java:171)
02-03 12:56:55.402: E/AndroidRuntime(17996): at com.example.bioderma.report.onViewCreated(report.java:71)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:908)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.BackStackRecord.run(BackStackRecord.java:833)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.Activity.performStart(Activity.java:5990)
02-03 12:56:55.402: E/AndroidRuntime(17996): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2279)
02-03 12:56:55.402: E/AndroidRuntime(17996): ... 10 more
02-03 12:56:57.830: I/Process(17996): Sending signal. PID: 17996 SIG: 9
请查看以下教程，这可能会对您有所帮助。
http://www.androidhive.info/2011/11/android-sqlite-database-tutorial/
此外，在类内执行查询时db初始化变量DatabaseHelper。
db = this.getWritableDatabase();