why does R does not exist error come in android?

问题:

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);

回答1:

Check if there are any errors in your resource files or any missing dependencies. Either of these will cause the R.java class to not be code-generated and thus a lot of errors like the ones you have shown.

回答2:

In my case, this error occurred because I had changed the package name of the app (before publishing to Google Play, of course), but I forgot to update the package attribute of the manifest element in my AndroidManifest.xml file. Once the package attribute agreed with the new package name, the error went away.

回答3:

Make sure you have: package 'YOUR PACKAGE NAME' in java file that calls R class

回答4:

1. Try Clean-> Build (If not just restart eclipse, it just worked!)
2. In case you are importing project, make sure you choose proper Level.

回答5:

If you are building from an ant script, you must run aapt. See the "-resource-src" target in $SDK_DIR/tools/ant/main_rules.xml.

回答6:

Also make sure to include your current Activity in the AndroidManifest.xml, inside the application tags. So if MyFile is your Activity subclass, you should have something like this in it:

<application 
    android:label="@string/app_name" 
    ... >

        <activity android:name=".MyFile"
            android:configChanges="orientation|keyboardHidden"
            android:label="@string/app_name">
            <intent-filter> 
                <action android:name="android.intent.action.VIEW" /> 
            </intent-filter> 
        </activity>
        ..


</application>

Although what's actually in there depends on your activity. More information about this at: http://developer.android.com/guide/topics/manifest/manifest-intro.html

回答7:

You can try import packagename.R;