adapter = new ListLeaderBoardAdapter(this, mLeaderboardlist);

adapter = new ListLeaderBoardAdapter(this, mLeaderboardlist);

what shall i do to this one?

This is my list adapter

你不能从片段中调用它。将其替换为 getActivity()。

像这样更改您的代码

adapter = new ListLeaderBoardAdapter(getActivity(), mLeaderboardlist);

试试这个

adapter = new ListLeaderBoradAdapter(getActivity(),yourArraylist);