Errors running builder 'android pre compiler' on

Today, this error always occurs when exporting a project. This is the case after repeated import and refresh operations...

The reference Android. jar file cannot be found in the project file, and the ADT and SDK are normal again, and the existing project is normal, that is, the exported project is faulty,

Later, I checked the. classpath file, which is a hidden file.

Compare the exported project and existing project files and find the following: <classpathentry kind = "con" Path = "com. android. IDE. eclipse. ADT. android_framework "/> is modified to JRE.

Modify again, OK. Done.

It should have been due to accidental deletion of the file from the project file.