Add image to Android project, error cannot be resolved or was not a field

SDK and ADT are version 22.6.2

Works for 4.4.2

Today, when writing Android code, adding a few pictures to the project, and then using the r.drawable call in the code, has been an error cannot be resolved or was not a field

Then I looked at the Gen directory of the R.java file, found that I have added to the image of the resource ID, it is very strange, is generally unable to generate R.java files when this phenomenon will appear ah

On the internet did not see the information can solve my problem, and then I took my code from start to finish again, and did not find anything unusual, suddenly, when I look at the file header code, found a suspicious code import Android. R; I try to delete this line of code, unexpectedly good, now for a moment do not want to understand why, but my problem solved, if there is any gaoren know, trouble tell Ah!