我正在使用sqlitedatabase，我能够正确插入数据，但问题是当我试图显示插入的数据时，我的应用程序崩溃并给出nullpointer异常，任何人都可以告诉我的代码有什么问题，以下是我的代码段，
此行中的错误
if (c1 != null & c1.getCount() != 0) {
MAinActivity.java
public class MainActivity extends Activity {
private ListView upcominglist;
private ListView todays;
private ListView eventhistory;
private ImageView addnewevent;
public ArrayList<ContactListItems> contactList;
public ContactListItems contactListItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
upcominglist=(ListView)findViewById(R.id.listview_upcoming);
todays=(ListView)findViewById(R.id.listview_todays);
eventhistory=(ListView)findViewById(R.id.listview_eventhistory);
addnewevent=(ImageView)findViewById(R.id.addneweventbutton);
addnewevent.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, AddNewEvent.class);
startActivity(intent);
}
});
contactList = new ArrayList<ContactListItems>();
contactList.clear();
String query = "SELECT * FROM PHONE_CONTACTS ";
Cursor c1 = SqlHandler.selectQuery(query);
if (c1 != null & c1.getCount() != 0) {
if (c1.moveToNext()) {
do {
contactListItems = new ContactListItems();
contactListItems.setSlno(c1.getString(c1.getColumnIndex("slno")));
contactListItems.setNameofevent(c1.getString(c1.getColumnIndex("nameofevent")));
contactListItems.setDtofevent(c1.getString(c1.getColumnIndex("dtofevent")));
contactListItems.setTimeofevent(c1.getString(c1.getColumnIndex("timeofevent")));
contactListItems.setDuration(c1.getString(c1.getColumnIndex("duration")));
contactList.add(contactListItems);
} while (c1.moveToNext());
}
}
else
{
c1.close();
}
c1.close();
String first=contactListItems.getSlno();
System.out.println("First" + first);
String second=contactListItems.getNameofevent();
System.out.println("SEcond"+second);
String third=contactListItems.getDtofevent();
System.out.println("Third"+third);
String fourth=contactListItems.getTimeofevent();
System.out.println("Fourth"+fourth);
String fifth=contactListItems.getDuration();
System.out.println("Fifth"+fifth);
}
Addnewevent.java
public class AddNewEvent extends Activity {
private int year;
private int month;
private int day;
static final int DATE_PICKER_ID = 1111;
static final int TIME_PICKER_ID = 11111;
int flag = 0;
private ImageView addnewdata;
private LinearLayout lnr;
private Button submit;
private EditText edtnmofevent;
private EditText edtdtofevent;
private EditText edttmofevent;
private EditText edtdurationofevent;
SqlHandler sqlHandler;
private ImageView datepicks;
private ImageView timepicks;
private Calendar cal;
private int hour;
private int min;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_new_event);
sqlHandler = new SqlHandler(getApplicationContext());
addnewdata = (ImageView) findViewById(R.id.addnewdata);
submit = (Button) findViewById(R.id.btnsubmit);
edtnmofevent = (EditText) findViewById(R.id.edtnameofevent);
edtdtofevent = (EditText) findViewById(R.id.edtdateofevent);
edttmofevent = (EditText) findViewById(R.id.edttimeofevent);
edtdurationofevent = (EditText) findViewById(R.id.edtdurationofevent);
datepicks = (ImageView) findViewById(R.id.calndrdat);
timepicks = (ImageView) findViewById(R.id.timepickrs);
cal = Calendar.getInstance();
hour = cal.get(Calendar.HOUR_OF_DAY);
min = cal.get(Calendar.MINUTE);
timepicks.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
showDialog(TIME_PICKER_ID);
}
});
final Calendar c = Calendar.getInstance();
year = c.get(Calendar.YEAR);
month = c.get(Calendar.MONTH);
day = c.get(Calendar.DAY_OF_MONTH);
StringBuilder dateValue1 = new StringBuilder().append(day).append("-").append(month + 1).append("-")
.append(year).append(" ");
// for Converting Correct Date format Save into Database
SimpleDateFormat sdf123 = new SimpleDateFormat("dd-MM-yyyy");
String abs1 = dateValue1.toString();
Date testDate1 = null;
try {
try {
testDate1 = sdf123.parse(abs1);
} catch (java.text.ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (ParseException e) {
e.printStackTrace();
}
SimpleDateFormat formatter1 = new SimpleDateFormat("dd-MM-yyyy");
String DateFormat = formatter1.format(testDate1);
edtdtofevent.setText(DateFormat);
edtdtofevent.setFocusable(false);
edtdtofevent.setInputType(InputType.TYPE_NULL);
datepicks.setOnClickListener(new View.OnClickListener() {
@SuppressWarnings("deprecation")
@Override
public void onClick(View v) {
showDialog(DATE_PICKER_ID);
}
});
addnewdata.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
LayoutInflater li = LayoutInflater.from(AddNewEvent.this);
View promptsView = li.inflate(R.layout.prompts, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
AddNewEvent.this);
// set prompts.xml to alertdialog builder
alertDialogBuilder.setView(promptsView);
final EditText userInput = (EditText) promptsView
.findViewById(R.id.editTextDialogUserInput);
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
lnr = (LinearLayout) findViewById(R.id.addnewlinear);
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
lp.setMargins(25, 0, 0, 0);
TextView valueTV = new TextView(AddNewEvent.this);
// valueTV.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
valueTV.setText(userInput.getText());
valueTV.setLayoutParams(lp);
valueTV.setTextSize(18);
valueTV.setTextColor(Color.parseColor("#2d6cae"));
LinearLayout.LayoutParams lp1 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
lp1.setMargins(25, 0, 25, 0);
lp1.height = 50;
EditText edtvalues = new EditText(AddNewEvent.this);
edtvalues.setBackgroundResource(R.drawable.rect_edt);
edtvalues.setLayoutParams(lp1);
lnr.addView(valueTV);
lnr.addView(edtvalues);
}
})
.setNegativeButton("Cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alertDialog = alertDialogBuilder.create();
alertDialog.show();
}
});
submit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(AddNewEvent.this, EventDetails.class);
startActivity(intent);
String nameofevent = edtnmofevent.getText().toString();
String dtofevent = edtdtofevent.getText().toString();
String timeofevent = edttmofevent.getText().toString();
String duration = edtdurationofevent.getText().toString();
String query = "INSERT INTO PHONE_CONTACTS(nameofevent,dtofevent,timeofevent,duration) values ('"
+ nameofevent + "','" + dtofevent + "','" + timeofevent + "','" + duration + "')";
sqlHandler.executeQuery(query);
System.out.println("Querys" + query);
}
});
}
SQL
public class SqlDbHelper extends SQLiteOpenHelper {
public static final String DATABASE_TABLE = "PHONE_CONTACTS";
public static final String COLUMN1 = "slno";
public static final String COLUMN2 = "nameofevent";
public static final String COLUMN3 = "dtofevent";
public static final String COLUMN4 = "timeofevent";
public static final String COLUMN5 = "duration";
/* public static final String COLUMN6 = "dlabl";
public static final String COLUMN7 = "dedt";*/
private static final String SCRIPT_CREATE_DATABASE = "create table "
+ DATABASE_TABLE + " (" + COLUMN1
+ " integer primary key autoincrement, " + COLUMN2
+ " text not null, " + COLUMN3 + " text not null, " + COLUMN4 + " text not null, " + COLUMN5 + " text not null);";
public SqlDbHelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(SCRIPT_CREATE_DATABASE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
答案 0 :(得分：2)
问题在于您的SqlHandler.selectQuery()返回null，另一个问题是检查结果：
if (c1 != null & c1.getCount() != 0)
您正在使用按位和&而不是短路逻辑和&&。在没有短路的情况下，评估c1.getCount()引用上包括null的完整表达式。
答案 1 :(得分：1)
这里有太多解释，所以我会给你一些导致空指针异常的缺陷。 我可以看到你的编程方法来自过于担心关闭事物和清理 资源到一定程度，它会造成问题。
contactList = new ArrayList<ContactListItems>();
// You are clearing your list, it should be empty, you have just created it.
contactList.clear();
String query = "SELECT * FROM PHONE_CONTACTS ";
Cursor c1 = SqlHandler.selectQuery(query);
// As mentioned by the other answer. You need && not &
// if (c1 != null & c1.getCount() != 0) {
if (c1 != null && c1.getCount() != 0) {
// Move to the first entry.
c1.moveToFirst();
//if (c1.moveToNext()) {
// do {
// Continue while it has not passed the last entry.
while (!cursor.isAfterLast())
contactListItems = new ContactListItems();
contactListItems.setSlno(c1.getString(c1.getColumnIndex("slno")));
contactListItems.setNameofevent(c1.getString(c1.getColumnIndex("nameofevent")));
contactListItems.setDtofevent(c1.getString(c1.getColumnIndex("dtofevent")));
contactListItems.setTimeofevent(c1.getString(c1.getColumnIndex("timeofevent")));
contactListItems.setDuration(c1.getString(c1.getColumnIndex("duration")));
contactList.add(contactListItems);
// Move the cursor along to the next entry.
cursor.moveToNext();
}
}
// Close cursor after while and within if (so you know it is not null).
c1.close();
}
else
{
// You can't close c1 if it is Null. This will throw and error. Lose the else.
c1.close();
}
// Move this to within your if statment.
c1.close();
来自您在聊天中提供的代码。 不要连续打开和关闭数据库，只需关闭完成后使用的每个光标。只需在程序运行的开始和结束时打开它。
public static Cursor selectQuery(String query) {
Cursor c1 = null;
try {
if (sqlDatabase.isOpen()) {
// You are closing the database.
sqlDatabase.close();
}
sqlDatabase = dbHelper.getWritableDatabase();
c1 = sqlDatabase.rawQuery(query, null);
} catch (Exception e) {
System.out.println("DATABASE ERROR " + e);
}
return c1;
}
您的项目还有许多其他缺陷。就像结构以及如何以及何时召唤事物一样。您需要将其模块化，为特定任务创建方法并调用这些方法，而不是在oncreate中使用大量代码。
我相信你会对此有很多疑问。但是目前这个问题正在解决你的空指针异常，这就是我将在这里讨论的内容。有关与此例外无关的问题，请提出新问题。希望这会有所帮助。