Android Development problem R file missing

Problem Resolution:
1. Sometimes when we open the Android project, we will find that the R file under the Gen folder is missing, which usually occurs after importing other Android projects because of the SDK version issue;
2. If the project is already in the Eclipse software, it may be caused by an XML file error.

Workaround:
1. Locate the "clean" button under the Project option in the menu bar and select the project you want to clean up in the popup dialog box;
2. If there is no effect, you can select the project name, right-click to select "Source code", "clean" to determine completion. Although the two are clean operation, but the feeling effect is not the same;
3. If the missing R file still does not appear, then you only need to restart Eclipse, you can see the auto-generated R file.