1. Error message
The error report shows that the SDK platform of android-28 cannot be found, that is to say, we have not installed the SDK platform of 28.
Two, the solution
1. Tools——>SDK Manager, open the SDK management page, check Android 9.0, and click Apply.
2. A prompt dialog box pops up, click OK.
3. Wait for the SDK to be downloaded and decompressed, and click Finish after completion.
4. Click the Sync button on the upper right again to build the project.
5. You can see that the build is successful.
Mapping new ns http://schemas.android.com/sdk/android/repo/sys-img2/03
to old ns http://schemas.android.com/sdk/android/repo/sys-img2/01 is Android The official told us that the system maps the new ns to the old ns because the latest gradle version is not used, and this problem can be ignored.