안드로이드 앱개발 중 문제가 생겼습니다.. 런타임오류인데요..타임피커 문제입니다..

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.Toast;
 
public class Cleaninfo extends Activity {
 private ArrayList<Custom_List_Data_clean> Array_Data = new ArrayList<Custom_List_Data_clean>();
 private Custom_List_Data_clean data;
 private Custom_List_Adapter_clean adapter;
 ListView listview;
 DatePicker mDate;
 String date;
 
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.cleaninfo);
  // DatePicker
 
  // TODO Auto-generated method stub
 }
 
 public void onClickButton(View v) {
  Log.i("Cleaninfo", "onClickButton");
  int id = v.getId();
  Intent intent1;
  switch (id) {
  case R.id.button1:
 
   final LinearLayout linear = (LinearLayout) View.inflate(this,
     R.layout.dial_cleaninfo, null);
   mDate = (DatePicker) findViewById(R.id.datePicker1);
   mDate.init(mDate.getYear(), mDate.getMonth(),
     mDate.getDayOfMonth(),
     new DatePicker.OnDateChangedListener() {
      public void onDateChanged(DatePicker view, int year,
        int monthOfYear, int dayOfMonth) {
       date = String.format("%d-%d-%d", year,
         monthOfYear + 1, dayOfMonth);
      }
     });
   new AlertDialog.Builder(this)
     .setTitle("청소 정보를 입력하시오.")
     .setIcon(R.drawable.icon)
     .setView(linear)
     .setPositiveButton("확인",
       new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog,
          int whichButton) {
         EditText content = (EditText) linear
           .findViewById(R.id.clean_content);
         data = new Custom_List_Data_clean(
           R.drawable.icon_lv, date, content
             .getText().toString());
         Array_Data.add(data);
         custom_adapter();
         adapter.notifyDataSetChanged();
        }
       })
     .setNegativeButton("취소",
       new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog,
          int whichButton) {
        }
       }).show();
 
   break;
  case R.id.button2:
   Toast.makeText(this, "삭제하려는 청소정보를 2초간 터치해주세요!", Toast.LENGTH_SHORT)
     .show();
   break;
  }
 }
 
 public void custom_adapter() {
  listview = (ListView) findViewById(R.id.listView1);
  adapter = new Custom_List_Adapter_clean(this,
    android.R.layout.simple_list_item_1, Array_Data);
  listview.setAdapter(adapter);
 }
}