ModuleNotFoundError: No module named 'mmcv._ext'

[2000LuoLuo]

I have tried all the methods in the issue, but still get an error. Does anyone know how to solve this?

python=3.7
pytorch=1.6.0 torchvision cudatoolkit=10.1
mmcv-full==1.2.2

Traceback (most recent call last):
File "./tools/test.py", line 11, in
from mmseg.apis import multi_gpu_test, single_gpu_test
File "c:\users\lht\desktop\edter-main\mmseg\apis_init_.py", line 1, in
from .inference import inference_segmentor, init_segmentor, show_result_pyplot
File "c:\users\lht\desktop\edter-main\mmseg\apis\inference.py", line 8, in
from mmseg.models import build_segmentor
File "c:\users\lht\desktop\edter-main\mmseg\models_init_.py", line 1, in
from .backbones import * # noqa: F401,F403
File "c:\users\lht\desktop\edter-main\mmseg\models\backbones_init_.py", line 1, in
from .fast_scnn import FastSCNN
File "c:\users\lht\desktop\edter-main\mmseg\models\backbones\fast_scnn.py", line 7, in
from mmseg.models.decode_heads.psp_head import PPM
File "c:\users\lht\desktop\edter-main\mmseg\models\decode_heads_init_.py", line 13, in
from .point_head import PointHead
File "c:\users\lht\desktop\edter-main\mmseg\models\decode_heads\point_head.py", line 6, in
from mmcv.ops import point_sample
File "C:\Users\LHT.conda\envs\open-mmlab\lib\site-packages\mmcv\ops_init_.py", line 1, in
from .bbox import bbox_overlaps
File "C:\Users\LHT.conda\envs\open-mmlab\lib\site-packages\mmcv\ops\bbox.py", line 3, in
ext_module = ext_loader.load_ext('ext', ['bbox_overlaps'])
File "C:\Users\LHT.conda\envs\open-mmlab\lib\site-packages\mmcv\utils\ext_loader.py", line 11, in load_ext
ext = importlib.import_module('mmcv.' + name)
File "C:\Users\LHT.conda\envs\open-mmlab\lib\importlib_init.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named 'mmcv._ext'