小编Tan*_*ndy的帖子

我是Android新手,我目前正在研究闹钟应用.但是当我运行它时,我得到了一个NullPointerException.任何人都可以帮助我吗？这是我的代码:

public class MainActivity extends ActionBarActivity {
    private Calendar c;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TextView textView=(TextView)findViewById(R.id.textview1);
        final Button setbtn=(Button)findViewById(R.id.setclock);
        final Button unsetbtn=(Button)findViewById(R.id.unsetclock);
        setbtn.setOnClickListener(new OnClickListener(){
            @Override
            public void onClick(View v){
                long current=System.currentTimeMillis();
                c.setTimeInMillis(current);
                int mHour=c.get(Calendar.HOUR_OF_DAY);
                int mMinute=c.get(Calendar.MINUTE);
                new TimePickerDialog(MainActivity.this, new TimePickerDialog.OnTimeSetListener() {

                    @Override
                    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
                        c.setTimeInMillis(System.currentTimeMillis());
                        c.set(Calendar.HOUR_OF_DAY,hourOfDay);
                        c.set(Calendar.MINUTE, minute);
                        c.set(Calendar.SECOND,0);
                        c.set(Calendar.MILLISECOND,0);
                        Intent intent=new Intent(MainActivity.this, CallAlarm.class);
                        PendingIntent sender= PendingIntent.getBroadcast(MainActivity.this,
                                1, intent, PendingIntent.FLAG_UPDATE_CURRENT);
                        AlarmManager am=(AlarmManager)getSystemService(ALARM_SERVICE);
                        am.set(AlarmManager.RTC_WAKEUP,c.getTimeInMillis(),sender);
                        String tmpS= format(hourOfDay)+""+format(minute); …