title: why does R does not exist error come in android?
body: <pre><code>packages/apps/Myfolder/src/com/android/myfolder/MyFile.java:196: package R does not exist
                    addPreferencesFromResource(R.xml.myfile);
                                                ^
  packages/apps/Myfolder/src/com/android/myfolder/MyFile.java:344: package R does not exist
          menu.add(0, MENU_SAVE, 0, R.string.menu_save)
                                     ^
  packages/apps/Myfolder/src/com/android/myfolder/MyFile.java:346: package R does not exist
          menu.add(0, MENU_CANCEL, 0, R.string.menu_cancel)
                                       ^
  packages/apps/Myfolder/src/com/android/myfolder/MyFile.java:454: package R does not exist
                       errorMsg = mRes.getString(R.string.error_empty);
                                                  ^
  packages/apps/Myfolder/src/com/android/myfolder/MyFile.java:458: package R does not exist
                       errorMsg = mRes.getString(R.string.error_empty);
  </code></pre>