private void showCoverDialog(){
    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle("提示");
    builder.setMessage("已經存在了今天的資料，確定覆蓋嗎？");
    builder.setPositiveButton("確定", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
        }
    });
    builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int i) {
        }
    });
    builder.show();
}