带有2个日期选择器的对话框 - 空指针错误

Question

这是我用来创建自定义日期选择器的代码：

public class ShoppingListDatePicker extends Activity{

    // These variables will hold the date values later
    private int startYear, startMonth, startDay, endYear, endMonth, endDay;
    DatePicker dpStartDate, dpEndDate;

public void showDatePicker() {
    // Inflate your custom layout containing 2 DatePickers
    LayoutInflater inflater = (LayoutInflater) getLayoutInflater();
    View customView = inflater.inflate(R.layout.custom_date_picker, null);

    // Define your date pickers
   dpStartDate = (DatePicker) customView.findViewById(R.id.dpStartDate);
   dpEndDate = (DatePicker) customView.findViewById (R.id.dpEndDate);

    // Build the dialog
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setView(customView); // Set the view of the dialog to your custom layout
    builder.setTitle("Select start and end date");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener(){
        @Override
        public void onClick(DialogInterface dialog, int which) {
            startYear = dpStartDate.getYear();
            startMonth = dpStartDate.getMonth();
            startDay = dpStartDate.getDayOfMonth();
            endYear = dpEndDate.getYear();
            endMonth = dpEndDate.getMonth();
            endDay = dpEndDate.getDayOfMonth();
            dialog.dismiss();
        }});

    // Create and show the dialog
    builder.create().show();
}


}

每当我从其他活动调用该方法时，我都会收到空指针错误：

抱怨Lauyout Inflater。我不知道为什么..... 我通过选择菜单上的按钮来调用方法：

case R.id.bShop:

            ShoppingListDatePicker shopListDatePick = new ShoppingListDatePicker();
            shopListDatePick.showDatePicker();
            break;

FullActivity：

public class ShoppingListDatePicker extends Activity{

    // These variables will hold the date values later
    private int startYear, startMonth, startDay, endYear, endMonth, endDay;
    DatePicker dpStartDate, dpEndDate;

    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);
        setContentView(R.layout.custom_date_picker);
    }
/**
 * Displays the start and end date picker dialog
 */
public void showDatePicker() {
    // Inflate your custom layout containing 2 DatePickers
   // LayoutInflater inflater = (LayoutInflater) getLayoutInflater();
    //View customView = inflater.inflate(R.layout.custom_date_picker, null);
   LayoutInflater inflater = (LayoutInflater) getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
   // LayoutInflater inflater = (LayoutInflater) getApplicationContext().getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
    View customView = inflater.inflate(R.layout.custom_date_picker, null);
    // Define your date pickers
   dpStartDate = (DatePicker) customView.findViewById(R.id.dpStartDate);
   dpEndDate = (DatePicker) customView.findViewById (R.id.dpEndDate);

    // Build the dialog
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setView(customView); // Set the view of the dialog to your custom layout
    builder.setTitle("Select start and end date");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener(){
        @Override
        public void onClick(DialogInterface dialog, int which) {
            startYear = dpStartDate.getYear();
            startMonth = dpStartDate.getMonth();
            startDay = dpStartDate.getDayOfMonth();
            endYear = dpEndDate.getYear();
            endMonth = dpEndDate.getMonth();
            endDay = dpEndDate.getDayOfMonth();
            dialog.dismiss();
        }});

    // Create and show the dialog
    builder.create().show();
}


}