Java 删除listView中的项时出错

我在这行中出错：

alert.setPositiveButton("YES", new DialogInterface.OnClickListener()

Logcat给出了这个错误

java.lang.NullPointerException

有人能帮我吗

//method to remove list item
private void removeItemFromList(int position) {

    final int deletePosition = position;

    AlertDialog.Builder alert = new AlertDialog.Builder(MainActivity.this);

    alert.setTitle("Delete");
    alert.setMessage("Do you want delete this item?");

    alert.setPositiveButton("YES", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            // TOD O Auto-generated method stub

            // main code on after clicking yes
            arr.remove(deletePosition);
            adapter.notifyDataSetChanged();
            adapter.notifyDataSetInvalidated();

        }
    });
    alert.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
        }
    });
    alert.show();

}

单击Yes（是），调用removeAt（deletePosition）

public void removeAt(int deletePosition) {
            arr.remove(deletePosition);
            notifyItemRemoved(deletePosition);
            notifyItemRangeChanged(deletePosition, arr.size());
        }

---

显示完整崩溃日志Slogcat在com.example.ina.medicalclock.MainActivity$3.onClick（MainActivity.java:122）@ρ∑ρk显示java.lang.NullPointerException，这是

MainActivity.java

中的行号122？arr.remove（deletePosition）；意味着

arr

为

null

，而且您的操作方式也不正确