!! Warning: This hanjie is a linea, it is only logical with the constraint that the picture consists of a single curved line, thus each black cell has exactly two of its four nearby cell blacks (except the two ends) !!

Baiubadu, baiubadu, baiubadu, baiubadu...
Here is the character who inspires me the name of this kind of grid.

Regarding the technics, here are the main things to know for now:
We can't have any 2x2 square nor any "T". Then, edge-logic can be used easier.
Moreover, when we have a turn, we can place cross in the angle. When we have a segment, we can place cross along the line (except in the extremities).
I add that any area which is isolated from the rest by cross is necessarily empty.
Let's go a little further, if both the ends are found, we must extend the curve "everywhere that is necessary".

Difficulty : ****

Tested, logical (as a linea).
Edge-logic can be usefull.
Once the 9 is in place, we can notice that the first cells blaken of R2 can't match with a 1. Else we would have a third end (what is not possible).
Good blackenage.