Question

我的程序包含一个名为date的按钮，用于显示日历视图。但应用程序在单击时结束。请给我一个解决方案。我的程序包含一个名为date的按钮来显示日历视图。但应用程序在单击时结束。请给我一个解决方案。

FirstActivity.java

package example.showevent1;

import java.text.SimpleDateFormat;
import java.util.Calendar;

import android.os.Bundle;
import android.app.DatePickerDialog.OnDateSetListener;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.support.v4.app.*;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.AdapterView.OnItemSelectedListener;

public class FirstActivity extends FragmentActivity implements OnItemSelectedListener, OnDateSetListener {
    /** Called when the activity is first created. */
    private static final String DATE_FORMAT = "yyyy-MM-dd";
    classdbOpenHelper eventsData;
    TextView userSelection;
    Button okButton;
    Button date1;
    public EditText date;
    private Calendar mCalendar;
    private static final String[] items = { "Yalahanka", "Rajai nagar", "Sivaji Nagar", "Koramangala", "RT Nagar", "Banashankari", "Yashwanthpura", "Hebbal" };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_first);
        okButton = (Button) findViewById(R.id.button2);
        date1 = (Button) findViewById(R.id.button1);

        userSelection = (TextView) findViewById(R.id.textView1);
        Spinner my_spin = (Spinner) findViewById(R.id.spinner1);// data1
        my_spin.setOnItemSelectedListener(this);
        ArrayAdapter aa = new ArrayAdapter(this, android.R.layout.simple_spinner_item, items);
        aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        my_spin.setAdapter(aa);
        okButton.setOnClickListener(new clicker());
        eventsData = new classdbOpenHelper(this);
        date1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showDatePicker();
            }
        });

    }

    static final String YEAR = "year";
    static final String MONTH = "month";
    static final String DAY = "day";
    static final String HOUR = "hour";
    static final String MINS = "mins";
    static final String CALENDAR = "calendar";

    private void showDatePicker() {
        Object ft = getFragmentManager().beginTransaction();
        DatePickerDialogFragment newFragment = new DatePickerDialogFragment();
        Bundle args = new Bundle();
        args.putInt(YEAR, mCalendar.get(Calendar.YEAR));
        args.putInt(MONTH, mCalendar.get(Calendar.MONTH));
        args.putInt(DAY, mCalendar.get(Calendar.DAY_OF_MONTH));
        newFragment.setArguments(args);
        newFragment.show((FragmentManager) ft, "datePicker");
    }

    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int pos, long arg3) {
        userSelection.setText(items[pos]);
    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub
        userSelection.setText("");
    }

    class clicker implements Button.OnClickListener {
        public void onClick(View v) {
            String datevalue = date1.getText().toString();
            String Userselectvalue = userSelection.getText().toString();
            SQLiteDatabase db = eventsData.getWritableDatabase();

            ContentValues cv = new ContentValues();
            // cv.put(classdbOpenHelper.KEY_COUNTED,
            // metersave.getText().toString());
            cv.put(classdbOpenHelper.KEY_DESC, Userselectvalue);
            cv.put(classdbOpenHelper.KEY_DATE, datevalue);
            db.insert(classdbOpenHelper.DATABASE_TABLE, null, cv);
        }

        public void onDestroy() {
            eventsData.close();
        }

    }

    @Override
    public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
        mCalendar.set(Calendar.YEAR, year);
        mCalendar.set(Calendar.MONTH, monthOfYear);
        mCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
        updateButtons();
    }

    private void updateButtons() {

        // Set the date button text
        SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT);
        String dateForButton = dateFormat.format(mCalendar.getTime());
        date1.setText(dateForButton);
    }
}

DatePickerDialogFragment.java

import android.app.DatePickerDialog;
import android.app.DatePickerDialog.OnDateSetListener;
import android.app.Dialog;
import android.os.Bundle;
import android.support.v4.app.*;
public class DatePickerDialogFragment extends DialogFragment {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) { 
        Bundle args = getArguments(); 
        Fragment editFragment = getFragmentManager().findFragmentByTag(FirstActivity.ACCESSIBILITY_SERVICE);
        OnDateSetListener listener = (OnDateSetListener) editFragment; 
        return new DatePickerDialog(getActivity(), listener, 
        args.getInt(FirstActivity.YEAR),
        args.getInt(FirstActivity.MONTH),
        args.getInt(FirstActivity.DAY));
    }
}

Answer 1

您正在获取Nullpointer，因为您从未实际初始化Calendar对象：

    mCalendar

应用程序在单击datepicker按钮时结束

1 个答案: