Question

尝试将日期选择器/时间选择器中的选定日期和时间插入SQLite。发生错误NewMeetingActivity.AddData（NewMeetingActivity.java:156）-布尔型insertData = myDB.addData（newDate，newTime）;

我目前将选择的日期和时间保存到文本视图中。然后如何将它们添加到数据库中？我尝试过将它们转换为字符串，但是我认为在应用崩溃时即时通讯功能无法正常运行

public class NewMeetingActivity extends AppCompatActivity implements DatePickerDialog.OnDateSetListener, TimePickerDialog.OnTimeSetListener {

    private Button btn_date, btn_time, btn_confirm_meeting, btn_back_to_meetings, btn_location;
    private CalendarView calendarView;
    private TextView myDate, myTime;
    DataBaseHelper myDB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_meetings);

        myDate = findViewById(R.id.myDate);
        myTime = findViewById(R.id.myTime);
        btn_date = findViewById(R.id.button_add_Date);
        btn_time = findViewById(R.id.button_add_Time);
        btn_confirm_meeting = findViewById(R.id.button_confirm_meeting);
        btn_back_to_meetings = findViewById(R.id.button_back_to_meetings);

        btn_back_to_meetings.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(NewMeetingActivity.this,
                                               MeetingActivity.class);
                    startActivity(intent);
                }
            });

        btn_date.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    DialogFragment datePicker = new DateFragment();
                    datePicker.show(getSupportFragmentManager(), "date picker");
                }
            });
        btn_time.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    DialogFragment timePicker = new TimeFragment();
                    timePicker.show(getSupportFragmentManager(), "time picker");
                }
            });

        btn_confirm_meeting.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    String newDate = myDate.getText().toString();
                    String newTime = myTime.getText().toString();
                    if (myDate.length() == 0) {
                        Toast.makeText(NewMeetingActivity.this, "Enter a date for your meeting", Toast.LENGTH_LONG).show();
                    }
                    if (myTime.length() == 0) {
                        Toast.makeText(NewMeetingActivity.this, "Enter a time for your meeting", Toast.LENGTH_LONG).show();
                    } else if (myDate.length() != 0 && myTime.length() != 0) {
                        AddData(newDate, newTime);
                        myDate.setText("");
                        myTime.setText("");

                    }


                }


            });


    }

    public void AddData(String newDate, String newTime) {
        boolean insertData = myDB.addData(newDate, newTime);

        if (insertData == true) {
            Toast.makeText(NewMeetingActivity.this, "New Meeting Created!", Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(NewMeetingActivity.this, "Something went wrong, Try again", Toast.LENGTH_LONG).show();

        }
    }


    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
        Calendar c = Calendar.getInstance();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, month);
        c.set(Calendar.DAY_OF_MONTH, dayOfMonth);
        String currentDateString =
            DateFormat.getDateInstance(DateFormat.FULL).format(c.getTime());
        TextView textView = findViewById(R.id.myDate);
        textView.setText(currentDateString);

    }


    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
        TextView textView1 = findViewById(R.id.myTime);
        textView1.setText("Hour: " + hourOfDay + "Minute:  " + minute);
    }

}

这是addData在我的数据库类中

public boolean addData(String item1, String item2) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put(COL2, item1);
    contentValues.put(COL3, item2);

    long result = db.insert(TABLE_NAME, null, contentValues);

    //if date as inserted incorrectly it will return -1
    if (result == -1) {
        return false;
    } else {
        return true;
    }
}
  database creation


public static final String DATABASE_NAME = "mylist.db";
public static final String TABLE_NAME = "mylist_data";
public static final String COL1 = "ID";
public static final String COL2 = "ITEM1";
public static final String COL3 = "ITEM2";

public DataBaseHelper(Context context) {
    super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createTable = "CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY 
KEY 
AUTOINCREMENT, " +
            " ITEM1 TEXT, " + "ITEM2 TEXT)";
    db.execSQL(create)}

Answer 1

读取错误：

Attempt to invoke virtual method 'boolean C/.myapplication.DataBaseHelper.addData(java.lang.String, java.lang.String)' on a null object reference

这意味着您正在尝试对一个为null的对象调用方法addData。在这种情况下，它是以下行：

boolean insertData = myDB.addData(newDate, newTime);

myDb永远不会在您的代码中实例化，因此尝试在其上调用方法肯定是行不通的。

尝试将日期选择器/时间选择器中的选定日期和时间插入SQLite

1 个答案: