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R.java disappeared

I recently downloaded the Android Support Package and have been using it trying to get my application, running at SDK 10, to use a GridLayout.
Anyway, I cleaned my project a few times working on this error in my XML files, and then when I went back to my classes in /src, every single reference to R.* was an error.
This has happened to me before, but it usually fixes itself, and it has not yet. Does anyone know what to do?
The R.java file is no longer in my /gen folder.

It sometimes happens when you import another project First i suggest you to build it, it will create automatically .
If it's not working then try to create new project from existing source and specify the downloaded project . It worked for me
Hope this works for you let me know..

Sometimes if there is an error in your XML files R.java won't build. Go through your XML files to make sure that everything is in order (typo, forgetting to close a bracket, etc). When you fix that it should build itself again.

You can also try Adnroid Tools>Fix Project. That may help you to create gen/R.java file

Follow following steps :
In Eclipse,
=> Right Click on Project > Android Tools > Fix Project
By this way, you can fix many common problems which can help generate R.java in gen/R.java file.

There can be several reasons why this occurs. The following I have found happen to me and I have included the steps I took to resolve them.
First step is to try and clean the project (from the Project menu option I believe)
Check there are no errors with your XML files. Sometimes this is obvious from the red 'x' that appears next to an XML filename in the Project exlporer window and sometimes it is not. If it is not obvious check the 'Errors' window (whic is founf in the 'Windows' Menu option
Failing that I have found that by disabling the automatic build option, adding some arbitrary comment to an arbitrary source file, saving the source file, clean the project, remove the comment and then re-selcting automatic build can work too.
Apologies for the approximate locations for some of the Eclipse functions but I am not currently in front of Eclipse to check.

This happens when you have an error in the res folder.
Fix the error first, then do :
Project --> Clean --> Ok
Et voila !

"R cannot be resolved to a variable"? [duplicate]

This question already has answers here:
Developing for Android in Eclipse: R.java not regenerating
(64 answers)
Closed 9 years ago.
In Eclipse, I've created a project from a source and now it shows errors - "R cannot be resolved to a variable". From what I found here, I had cleared and rebuilt the project, but still the R file doesn't appear in the /gen folder.
Any ideas?

Dont worry. First you may clean the project, then run the project. If this does not work then follow the following links:
Here is the best way to solve this problem: [Android Development- Where is my R.Java file?][2]
R.java not regenerating
R cannot be resolved - Android error
R cannot be resolved to a variable
R cannot be resolved to a variable -- mailing list entry
Fixed: R cannot be resolved to a variable

If Clean/Rebuild Project doesn't work try to check our package name in AndroidManifest.xml.
The problem "R cannot be resolved" happens when you change your package name in the AndroidManifest.xml file. It uses your Android package name to create a subdirectory under the "gen" directory where it stores the R.java file.

For me the error got fixed by making some changes in Android SDK Manager.
Whatever be the latest API level available, install its "SDK Platform". For me latest API level available was 16, so I installed its's SDK Platform as shown in the image below. It works fine now.
Cheers, Mayank

Did you just update both sdk and adt(from 21 to 22), then you need to install a new item: Android SDK Build-tools
Refer to:
Eclipse giving error, missing R.java file after recent update

For me somehow the Project properties; Android; Project Build Target was not set. I chose a Android version there (e.g. 4.2) and it fixed it.

for me, the best solution to suggest to people that have problems with the "R" file would be to try the next steps (order doesn't matter) :
update ADT & SDK , Eclipse and Java.
remove gen folder , and create it again .
do a clean-project.
right click the project and choose android-tools -> fix-project-properties .
right click the project and choose properties -> java-build-path -> order-and-export. make sure the order is :
Android 4.3 (always the latest version)
Android private libraries
android dependencies
your library project/s if needed
yourAppProject/gen
yourAppProject/src
make sure all files in the res folder's subfolders have names that are ok : only lowercase letters, digits and underscore ("_") .
always make sure the targetSdk is pointed to the latest API (currently 18) , and set it in the project.properties file

For me, there was a missing slash at the end of my SDK. In Eclipse > Preferences > Android > SDK Location
For example, change
/home/matt/android-sdk-linux
to
/home/matt/android-sdk-linux/

your android manifest must start with correct package
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="HERE - Correct package NAME"
android:versionCode="1"
android:versionName="1.0" >`

I got similar problem and solution I found out was in resources any of
the file aka background, sound etc must not contain capital letters or
any special symbol other than _

What you really need to do it just install "build-tools" from sdk manager,
and r.java will be generated automatically.

I had the same error. Error was that, I had placed a file in res/raw folder with invalid filename.
As soon as I corrected the file name to a valid one, error was resolved!
Allowed characters for naming a file:-
1. a-z
2. . _
3. 0-9
4. no capital letters
Capital letters were the issue in my case!

Sometimes you can accidentially add an import to "R", so if at the top of your code you see some weird import about that that you did not add yourself, delete the reference, and everything should go back to normal

My problem was strange and took some time to find. Somehow the package of the src file changed so that the last entry in the package was deleted. So for example initially my class MyActivity.java was in package com.abc.client.test.app but after I added a user permission, the app got removed and the package was renamed to com.abc.client.test. I don't know how it happened. Renaming the package and putting the java file in the correct place fixed the problem.

I found this problem when trying to run the Notepadv3 programme from Googles 'first lesson'..
For me it was an issue with the xml file, due to the API level I was using. I renamed each case of Match_Parent to the older type of Fill_Parent. Oh and if you have already auto-built the project then you need to delete 'import android.R' on NoteEdit.java and Notepadv3.java, clean the project (click 'Project', then 'clean...') before saving.
Solved it for me. Came from this post Android NDK r4 san-angeles problem
Can't believe Google dosen't warn of this problem - I have been setting up another PC to start programming again and even with a bit of prior knowledge this was a pain.. How do you set the API when importing an existing project??? Can't see where there is any dialogue option when you 'File' 'Import' etc ..
Scamparelli

Check the androidmanifest.xml file and layoutfolder xml files. They should be created properly as the starting and ending clause in xml should be placed properly. Update the files, clean and build. And all set!

I had this problem and none of the other guides helped, and then I realized I didn't have the java jdk installed on my system. If you haven't done this either go download the version corresponding to the version of eclipse you installed (x86 or x64)

It is possible you have an error in your *.xml files: layouts and etc.

Try to modify AndroidManifest file.
For example add space and delete this space. After this OPERATION, save project. Resources will be refreshed. It can help.

I solved the problem with resolving R resource on fc19.x86_64 and ADT v22.0.5-757759 by installing additional libraries after Fedora and ADT upgrade.
yum install ld-linux.so.2
yum install libstdc++.so.6
yum install libz.so.1
Those libraries are required by adb (Android Debug Bridge version 1.0.31).
Then restart Eclipse and perform project clean Project->Clean check project you would like to clean.
Hope it helps :)

Project > Clean...
usually regenerates R.java file located in gen/com.mypackage

In my case, R.java wasn't getting generated because of a hierarchical parent error, which in turn was cured by updated one or more Eclipse plugins (Go Eclipse-->Help-->Check for Updates)

I got this error when I added a js file to the res folder.
An error indicator was set on the res folder icon. In all the classes where I used R I got this error.
I moved the js file to the assets folder and everything worked.

Problem was eclipse was not generating R.java.
To resolve this issue please go to project->clean... and select your project and select ok and then clean and build project and import your package name R file(Ex com.demo.R). It works.

This can happen when the android naming convention isn't followed. Check if you have placed a file/photo into one of the android folders and make sure that the file name contains only lower case letters

I know this is an old question but I just solved my own version of it and perhaps this might help someone.
After two days of tearing my hair out with this, I finally got around it by deleting the raw folder, then recreating it and dropping the file(s) back in.
After that, another Project > Clean and it at last compiled.

I got this when I renamed a project. Although the project is renamed, some references are not. Clearing lint, and then rerunning lint helped. (Right click project > Android Tools > Clear Lint Markers, then Run Lint)

My setup was broken after a recent update where the SDK build tools need to be installed separately after the SDK installation. So build tools update + Eclipse restart fixed this for me.
Credit goes to the Android reply here

When other solutions fail, select your project and delete it. MAKE SURE YOU DO NOT REMOVE FILES FROM DISK.
Then use file>import>existing android code into workspace, and select the location of your project.

I been having this and i did trace it back to the layout files.. It happend to me again however i could not find noting in the layout files. I looked in the string.xml and there was it.. one of the string names started with cap and that was causing the problem.

Fix any XML formatting errors in the XML Files in your /res/menu folder.
Might be a compile time error from the XML file being improperly formatted.

Your project contains error(s), please fix it before running it

I am developing a simple Android application. But when I run Eclipse, it shows the following error:
Your project contains error(s), please fix it before running it.
I can't find any error in my project or there is no error in my application.
There is a red cross under the application name but it is not under another file name.
Does anyone else have this issue?

That usually comes from errors in the build path.
If you're using eclipse, there is a view you can add that lists all the errors called "Problems":
Otherwise, you can try to clean the project, and that usually solves a few problems.
Finally, if you add or alter resources from outside your IDE, you'll want to reload the resources and clean.
EDIT (Comment by anonymous user)
This can also be caused by an out of date "Debug Certificate" fixed as follows:
IF ALL FAILS THEN THIS GOTTA BE THE SOLUTION:
Delete your debug certificate under ~/.android/debug.keystore (on Linux and Mac OS X); the directory is something like %USERPROFILE%/.androidon Windows.
The Eclipse plugin should then generate a new certificate when you next try to build a debug package. You may need to clean and then build to generate the certificate.
This is also another fix for the "setContentView(R.layout.main);" error that says it cannot find R.layout.main when it is actually generated. (R cannot be resolved to a variable).
This is also another fix for the error "Your project has errors..." and you cannot find any.
Clean and rebuild are still necessary after generating a new debug certificate.

First go to Window -> Show View -> Error Logs in menu. It will display error logs if you have any. Then try to clean the project and build it again.

Well, in my case some libraries were addressed twice in the:
Project >> Properties >> Java Build Path >> Libraries
I just had to remove the duplicate and it worked fine without any cleanings or refreshing.

I saw this with an existing project. I had made a few edits, but hadn't imported anything new. Restarting Eclipse didn't help.
Project->Clean did solve the problem.

I come across this error often when I import a new project in my workspace.
Reason: Some necessary files (Like R.Java) is not generated in its respective packages.
Cure: Clean and build projects, All the files that needs to be auto generated will be there on place after building the project.
Best Luck.

This is happened to me. After format of my system,
When i import project it shows same error
remove first debug.keystore file then goto -
Project -> Project properties -> select library -> remove -> add again libraries.
It's working for me......

Go to projects menu, click on clean menu item.
After that close the eclipse and reopen and try compiling..
It is software glitch you find some times.

it can also happen if you move required files. Simply check Problems View (menu window -> show view -> Problems) as told here

I had this exact same problem. One solution that would work would be to create a brand new project, but I don't think there's any need for that. For me the problem was that the debug certificate that gets auto-generated had expired. Deleting this file allowed Eclipse to rebuild that file, which solved the problem. You can't run an app with an invalid certificate, whether it be a debug or release certificate. Note that cleaning my project did not work. For more information, see:
"Debug certificate expired" error in Eclipse Android plugins

Recently I came across this error. I was really in a corner with no help, then I figured it out. This error can occur for the following reasons:
An error in the project code
Improper linking of external library files to the project
Most important: if your debug.keystore file is expired.
The first 2 cases are easily identifiable but the third one is like searching a black box in a dark room.
So in addition to Project -> Clean, remove your debug.keystore file also.
I am using Mac + Eclipse so to remove, I wrote the command rm ~/.android/.debug.keystore in a terminal.

Is there a way to ignore existing errors in project. Something similar what eclipse allows in case of java projects.
In my case the errors exist in jni directory. The errors are shown even though ndk-buid succeeds. So all i want to do is to ignore the errors reported by eclipse.
If the errors are indeed errors then i should get unresolved symbols during ndk-build.
I have ensured standard android includes are there in include path.
Also my project is of type android/c/c++.
I have two builders associated with the project
1. statndard android builder
2. custom ndk builder that ive explicitly created.

Simulate your self some error in class. Then save it and it would show more errors than you simulated. For me it was incorrect import and this helped.

I have had a similar problem.
Under "problems" tab I have found an error saying "Error generating final archive: Debug Certificate expired on 2/22/12 1:49 PM"
So my advice is to look in the problems tab to get some more info.
Bye

If none of the above solution work, you should check the READ ONLY property of the Project folder, if it is Read-Only, the compiler will not be able to overwrite the resources, R.java and other dex APK etc files and hence this will occur..
This happened to me and I fixed after a long struggle..
Happy Programming.

For some reason eclipse only showed a ! error on root and didn't specified what error it was.
Go in Windows -> Show Views -> Problems. You might find all previous errors there, delete them, do a clean build and build again. You'll see the exact errors.
Eclipse shows an error on android project but can find the error

I had this exact problem when trying to run the Doodlz app, from the book Android for Programmers, on Mac OS X with Eclipse Juno.
After downloading and unzipping the demos from the book, I forgot to change the permission of the files. They were read-only on my system so this was the first issue.
The second issue was solved by selecting a build target on Eclipse. This was fixed by going to: Project > Properties , and clicking the Android field on the left panel to be able to select one option as the Project Build Target, which in my case was:
Target Name Vendor Platform API Level
> Google APIs Google Inc. 4.0.3 15
Then cleaning and rebuilding the project showed no errors.
Finally, to run the app right-click the package (at the Package Explorer tab) and then select:
Run As > Android Application

Simply Deleted my debug certificate under ~/.android/debug.keystore and Project->Clean did solve the problem.

Delete the .android folder from your Documents&settings\User\ on XP and \User\ on Win7. Recreate the AVD again and create a new project.

What caused this problem for me was none of the above, but simply that I'd left the "debuggable" attribute to false in the manifest.xml file after doing a release. D'oh!
Of course neither the LogCat, Error log, Console, or Problems window alerted me to this..

I had the same error, when I copied a project to another computer.
I then checked all properties of the project on both machines, and the only thing that was different was the order of items in Java Build Path - tab Order and Export.
I moved the items Android X.X.X and Android Dependencies above the other 2 in the list (in my case, src and gen folders) and voila, it worked again!
I'm not really sure if the different order was actually the problem, but at least changing it (and saving the properties again) seemed to help...

I had the exact same problem after updating the SDK and ADT.
My issue was resolved by deleting the .android folder (hidden) under C:\Users\USERNAME\

This happened to me when I was experimenting with Maven.
Right click project -> Maven -> disable maven nature
corrected the problem for me.

Yes, this is a rather cryptic message. If you've got a faulty project (say one you've been working on in the past) then you'll get this message (and no messages in your current project's Problems / Error Log panes).
You may just want to run your current project. This may be perfectly fine. Just click on the down arrow to the right of the Run button to select your project.

Try changing your workspace. I am not sure this is the exact solution . I did face the same issue for sometime untill i changed my workspace.

In my case, it happens with ADT 22.
I choose not to create Activity.
After I remove the "appcompat_v7" as library project. I works.

I had similar problem where I couldn't run my project yet didn't see any problems in the code. In Error Log panel it said something like "Cannot add P/ to the list of segments P/ in as a parent".
Restarting Eclipse solved the problem.

How to generate R.java

I downloaded few source codes from Google source codes.
I executed them on Eclipse but R.java file is not created and therefore I got many errors saying that R cannot be resolved. There is no main.xml in layout too. Some other XML files are there. How can I execute these programs?

As long as you have a valid Android project, you can use aapt package to generate the R.java from resources. Here's example usage (all should be in one line):
aapt package --non-constant-id -f -m -M <abs_path_to_AndroidManifest.xml>
-S <abs_path_to_res_dir> -I <abs_path_to_platforms_android.jar>
-J <abs_path_to_dir_that_should_contain_gen_R_java)
--generate-dependencies
The above can be made scriptable using ANT by using the aapt target or by simply using an exec target.

Presume you have Android sdk. If you have.. just clean the project. R.java will be autogenerated.

Hi I just faced the same problem. The file R.java is deleted an regenerated each time you clean the project. In my case there were some errors in one of .xml files and no R.java was generated. If you did not have Main.xml that might be the reason. anyway if you fix .xml problems R.java should be generated.

Open Android SDK Manager
Tick Tools that there are 3 packages of Android SDK Tools , delete and install them again.
When they are finished, please refresh your project in Package Explorer.
You will see BuildConfig.java and R.java in /gen
I think you wanna need that I recommend this comment
Enjoy with your building app.

After few hours frustration finally I have decide to remove the red marks from the my file where it was not able to resolve the R.java as it was not actually available in my code. After removing the first red line from my activity file the project builds and generated the R.java automatically.
This is something really freaking thing for me as it goes without any reason and came back with the same thing.

If your build.xml includes the "-resource-src" target (which it will if you include $SDK_DIR/tools/main_rules.xml or lib_rules.xml) you can rebuild it with ant.

For future readers, restart adb then clean.

Correct all errors in the Xml layouts, if the errors is only in the id attribute, change to other name an save, then type the original values, this solution works for me.

I encountered this issue after adding a jpg file with a numeric file name into my drawable folder. I was getting a compilation error, " expected on line y" when trying to rebuild the project after cleaning it. You may want to check that you do not have a similar issue. Although I encountered this while using Android Studio, I am sure it would affect Eclipse as well.

Cleaning the project, delete the R.java and regenerate it.
If you have an error anywhere in your /res file (the resources) , the R will not be generated usually.
It could be an error in the name of a picture , or anything ...
fix your errors before.
good luck ;)

I have encountered similar problem and i changed the workspace folder and all errors disappeared. It's sort of simple solution but it works.

R.java disappears after project clean

After I added some .png files into my Project Workspace drawable folder I refreshed my drawable folders in Eclipse and the newly added files showed up. But when I tried to access those resources using R.drawable.xyzimage, xyzimage although in the folder could not be resolved.
So I did a Project Clean and guess what after this clean R.java is totally gone and all my classes accessing resources using R.java is showing all sorts of error and Eclipse won't let me run the code anymore.
I have backup of my source code but I want to explore if R.java can be regenerated and how?
Thanks for all the help.

Try Project->Clean in Eclipse. In my limited experience if R.java is not being automatically created then there is an error somewhere in your xml. Triple check everything.

You have to build the project to be able to use the newly added resources.
Cleaning a project removes all auto-generated files. Building the project it should automatically create them. When you Clean a project, there's an option to start a build immediately after clean up.
Here's a few things you can try (did the same procedure after manually deleting the "gen" directory.
After you have deleted the gen directory, go to Project > Clean ...
You should have errors indicating that R cannot be resolved to a variable. Right click on your project from the Package Explorer and select Build Project. Be sure Build Automatically option is turned off (uncheck in Project > Build Automatically).
Errors regarding R should have now disappeared. Now, perform a Project Clean once again. All errors should be gone.
Let me know if this works for you.

Here is what the problem was. I added those new png images to the project and android has rules as to what characters are allowed in the names of these images. Once I changed the uppercase letters in the image name, it was back on track again and Build Automatically generated the R.java file and all errors were gone. Eclipse console is the place where I found all the errors related to my resources.
Thanks Guys....I tried your solutions but my error was something specific which was due to my image naming convention so this is the way I fixed it.

I would agree this is usually a XML problem but moreover that it is something within your res folder that is the problem and may be highlighted with a red cross after the clean attempt.
I have just had this problem and it was because I had created my own folder called 'data' within res folder. After the clean it had a little red cross against it. I removed this folder and R built again.
Regards,
Mark

Several things you should check in your project:
Check the Problems tab in your Eclipse IDE. Are you sure that you did not introduced building problems while making changes with drawables? To check that you need to check xml source of affected layout and see if something is marked red.
In File explorer go to the directory where your Android project is. Check that you have file default.properties (.classpath, .project and AndroidManifest.xml should be there). If default.properties is missing it may be easily replaced by correct version.
Which is the Android version you are working with? If that is 1.5 or lower be sure that in the res directory you have directory named drawable, not drawable-hdpi, drawable-mdpi and drawable-ldpi. Last three are valid for version 1.6 and higher.
Right click on your project in Package explorer in Eclipse. You will get a number of options. Go to Android Tools-> Fix Project Properties so see if that helps.

I had an invalid jpg in my res/drawable folder. I removed the jpg and it worked.

I had this problem on my Mac too and I think it could be good to know for all Mac users how I managed to solve this error.
I had a .DSStore file automatically imported to my project inside the res directory and when I removed it and rebuilt the project all went well.

Everytime you clean the project and it rebuilds, it imports
import.android.R
so, delete this import and remove all errors from xml files. It will work.

This happens to me if I move my project to a new location. I have found that the answers above didn't fix my problem, but that creating a new project and importing the source did.

This may be simple but check to make sure you don't use
import android.R;

If you add an external resource file with capital letters for example
"Hello.png or WelcomeSound.mp3 etc etc" like if you add upper case letters and clean your project you'd surely loose your R.java file. So if you already lost it, either rename the file externally and then clean your project or else right click on the project Refractor->Rename and then rename your file with all letters in lower casing. Next, delete the 'gen' folder in the project explorer and now right click and "Build Project". If Build Project option is grayed out, go to Project-> Deselect "Build Automatically" option.
Regards,
Kshitij Thube

Check at the Console View If there in message Error, It will Help you to find out the source of the probleme.
I had i similar probleme and i find out that the probleme was from the pic name even if the name respect the Syntax so I change it to img1 and it worked fine.

Try editing one line of code in your project, then build the project once more.

Another thing: never try to run an application with the texteditor opened with a xml file. That will create a wierd run configuration that can only be fixed by project clean-up and sometimes can make the xml file to vanish (happened to me twice already).

All my R.* files stopped working after I did a Project->clean in Eclipse. The issue was that I backed up a XML file attached to one of my activities in the layout directory. This causes errors in every activity of my project.
After deleting the file I still had R errors in one of my Activities and it only was resolved after I tried importing different files and then deleting them. I actually made no change to the previous imports but for some reason deleting them all and re-pasting them fixed it.

I have got the same problem after lots of cleaning and building project again and again. I found that on console there is this error:
res/drawable-hdpi/Blue Blank.png: Invalid file name: must contain only [a-z0-9_.]
and this is not appearing as an error in xml. I changed the name and save the file, clean project and build. Now it's working. My suggestion check your res folder and name of files you use in it and name only [a-z0-9_.].
Delete related tag in xml, save xml, clean project, build project. Now again put that resource in xml and save!

Check your file in drawable folder ensure that all are resource file (image) remove unwanted file Like thumb.db. Remove those all files and check again

Make sure your png files have lowercase names. That is what kept throwing mine out, because I capitalized the first letter, or I used an unallowed non alpha numeric in the naming. Check that before destroying any of your code.

just check your image folder (usually created res > drawable files) and be sure dont use capital letters on .png files, every type must be in small letters then you can find again your R.java under the gen file folder

i removed 'import android.R;' then commented out the offending lines, then did a build, ok
then i removed the comment and it fixed it

I had the same problem when I cleaned my project. I got crazy to solve it, I searched and searched but solved it in my way.
First of all, delete all needless files in your /res folder. I had some notes in it, I took them to another project that I don't work on it and build the project manually. It worked! Try this I'm sure it will help.
Good developing!

Was there an XML file with the naming convention of "somthing.out.xml" generated? If so you should delete this file (an unwanted file of this name can cause major problems for your somthing.somthing.R file import).
In some versions of eclipse (I know eclipse javaEE does this for sure), running the project while viewing an XML file will create a file called filename.out.xml in your res->layout folder. You must delete this generated file if this has occurred otherwise you wont be able to get the java.R file to import.

Try Project -> check Build Automatically

If you are using 64-bit Ubuntu, try to install the 32-bit libraries (ia32-libs)
$ sudo apt-get install ia32-libs
it worked for me

This exact same thing happened to me. coincidentally I needed to update my adk that day, so i did so and after restarting eclipse it worked again. My recommendation would be to build the project and restart eclipse. It is not due to any error in your code.

I read and tried many of the above after simply doing a clean on one project. Eclipse would not build anything afterwards.
Fortunately I had last-nights backup of the workspace and my source is copied in from VS 2010.
No more cleaning!

Delete your project from workspace witout source deleting and then import it into workspace.
RightClick on your Project -> Delete /Don't select "Delete project content on disk (cannot be undone)"/ -> Ok
File -> Import -> General -> Existing Projects into Workspace -> Brouse -> /Look for your workspace(!) folder/ -> Ok -> /your cleaned project will be automatically checked/ -> Finish

I had the dreaded missing R problem yesterday with Eclipse Juno after a routine clean. StackExchange is full of suggestions and extensive googling revealed only the usual suspects (XML naming conventions problems, etc) none of which seemed to apply directly, although it is certainly possible I missed something.
The best summary comprehensive list of possible causes and fixes was here:
http://www.techrepublic.com/blog/software-engineer/a-comprehensive-troubleshooting-guide-for-androids-r-cannot-be-resolved-error/
One useful tip there was to try to create and run a simple "Hello World" in my workspace. If that does not run, the setup is corrupted. My Hello World was just as full of errors as my custom app.
The solution that worked for me (perhaps great overkill but nothing else worked) was to completely uninstall Android SDK and delete Eclipse (Juno), download Eclipse for Developers (Kepler) and reinstall Android ADT plugin and ADK and recreated my AVDs using the latest "compile with" version in options.
So far so good, although I am recreating the app from scratch. I will be more cautious about using clean from here on.

I have same problem occur just now I renamed invalid png file like *demo.1.png as demo.png * and its work.

Proven successful method, check the file (AndroidManifest.xml) and delete all comments in it, and make sure there are no errors in this file, I tried and did work with me.