private void showCoverDialog(){
    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle("提示");
    builder.setMessage("已经存在了今天的数据，确定覆盖吗？");
    builder.setPositiveButton("确定", 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();
}