R cannot be resolved - Android error

user_61996 0
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I just downloaded and installed the new Android SDK. I wanted to create a simple application to test drive it.

The wizard created this code:

package eu.mauriziopz.gps;

import android.app.Activity;
import android.os.Bundle;

public class ggps extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
}

but Eclipse gives me the error

R cannot be resolved

on line

setContentView(R.layout.main);

Why?

PS: I do have an XML file named main.xml under res/layout/.

android-sdk-tools android-resources compiler-errors eclipse android
108 Answers

Each time I had a problem with R not been generated, or even disappeared, this was due to some problem in the XML layout file that prevented the application from being built.

user_2319570

my project have include a r.java.at the beginning ,R.layout.main work good.But,after adding some code it doesn't work,and the error is R.layout.main can't resolved.what's the problem?

Look at your imports. Chances are that the line:

import android.R;

will be there. If that's the case, remove it, so that your project will resolve R not with the default Android Resources class, but with the one auto-generated from your /res/ folder.

user_1449690

What Will said was right

R is an automatically generated class that holds the constants used to identify your >resources. If you don't have an R.java file (it would be gen/eu.mauriziopz.gps/R.java in >Eclipse with the 1.5 SDK) I would recommend closing and reopening your project or going to >Project > Build all (and selecting "Build Automatically" while there as recommended by >Josef). If that doesn't work than try making a new project, if the problem is recreated than >post here again and we'll go into more detail.

but I've found out that there was another problem that was causing the first one. The tools in the SDK directory didn't have the permissions to be executed, so it was like the didn't exist for Eclipse, thus it didn't build the R.java file.

So modifying the permission and selecting "Build Automatically" solved the problem.

user_619960

R.java is a file that the Android Eclipse plugins creates while building your application. R.java is created under the "gen" directory. This file is generated from the information in the "res" directory. If you run select "Project" -> "Clean..." on the Eclipse menu, it will remove and then regenerate the R.java file.

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.

Eclipse may have problems executing clean, because it is confused about where the R.java file is when you have changed the Android package name. You can either rename the subdirectory under gen to match your new package name, or you can change your package name back to the old name. Do the clean and then change the package name to the new name you want. This works best if you stop Eclipse from trying to build while you are changing the package name. Under the "Project" menu uncheck the option to "Build Automatically" and also when the "Clean..." dialog asks if it should "Start a build immediately" uncheck the box so it doesn't try to build while you are changing the package name. After you have changed the name you can turn "Build Automatically" back on again.

Note that if your AndroidManifest.xml file package name does not match your Java package name, Eclipse will end up automatically adding an "import <your Android package name>.R;" line in all your .java files that have any references to R. If you change your AndroidManifest.xml package name, sometimes Eclipse does not update all of these added imports. If that happens, use the Eclipse refactoring (ALT + Shift + R) to change the import statement in one of your Java files to your new AndroidManifest.xml package name. It is best to do this while you have disabled "Build Automatically".

Admin1

R is an automatically generated class that holds the constants used to identify your resources. If you don't have an R.java file (it would be gen/eu.mauriziopz.gps/R.java in Eclipse with the 1.5 SDK) I would recommend closing and reopening your project or going to Project > Build all (and selecting "Build Automatically" while there as recommended by Josef). If that doesn't work than try making a new project, if the problem is recreated than post here again and we'll go into more detail.

Will_534980

R is a generated class. If you are using the Android Development Tools (ADT) it is generated whenever the project is built. You may have 'Build Automatically' turned off.

user_984010

You may need to update SDK tools. Relaunch Android SDK Manager again and install a new item: Android SDK Build-tools.

enter image description here

user_17540200

In case anyone is interested (I might be saving your life here), I had the error, R.xml cannot be resolved, slightly different on a GLS project. Hmmmm. After looking in R.java, I found an auto-generated class, XML.java, (I think) was not there.

Solution? It needed a new folder in res: res\xml and a file called default_values.xml in there. Then all was OK.

Just in case you have not got that file, it's:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android">
</PreferenceScreen>
user_2585610

My problem was that I left out the = mark from the strings in strings.xml e.g. <string name"dialog_grl... It did not appear to me even when the graphical layout of my .xml file could not show the strings. After a project clean all files got messed up.

user_5716480

There are several reasons of R can't be resolved.

  1. Most of time this error occur for XML file fault. This error can be solved by Clean and rebuild your project, also you can restart your android studio.

  2. Sometime If you codeing some wrong thingin AndroidManifest, this error can be occur so Please check this.

  3. If your resources contain the same name or they have invalid characters, this error can be occur.

If you already check those and yet you are facing with same problem then go ahead:

This error can be occurs when Android Studio fails to generate the R.java file correctly, so you have to follow those steps:

Step 1: Safely delete the build folder from app directory.
Step 2: In Android Studio, File -> Invalidate Caches / Restart
Step 3: Build -> Clean Project Then Build -> Rebuild Project.

so build folder will be regenerated and hope so error is gone.

If Error still found then maybe you have performed refactoring the package name previously. This case you can press ALT + ENTER together for import the R.

user_98155190

1) First of all close all the file.
2) Go to the Build -> Clean Project.
3) Go to the Build -> Rebuild Project.

This works for me.

user_107897220

I had the same issue, but couldn't find out what xml file caused the error.

Thanks to this post I installed build tools 18.1.1 instead of 19 and it showed me the defective file. It seems that version 19 doesn't show the actual error.

Hope it helps someone :-)

user_20140800

Just Restart Your Project

File>>invalidate caches /Restart

Note:

  1. Android automatically creates a .R file not need to import
  2. Import android.R.* << R.java file auto created by android Studio
  3. Android studio has lots of caches hold and that's why some time it's occurred
user_90337350

Another way this can occur is if you start a new project from one of the samples. When you later decide to change the package name from com.example.android.foo to your own domain, you will need to modify several values in the manifest and in individual .java files.

If you're in Eclipse, find the package statement for the .java file and choose QuickFix. There may be several choices there, but the one you want is the one that indicates to "Move 'foo.java' to package 'com.youdomain.android.yourapp'. Save the file and it may autobuild or do as others have suggested and try "Project->Clean".

user_2967580

Of the many possible problems that could cause this, this is what fixed it for me.

Right click on project -> properties -> Java Build path-> source.

Then add the gen and src folders. For some reason, Android wanted me to only have the overall folder.

user_8363660

I had tried all of the above with no prevail. It turned out PhoneGap was causing a conflict with the Android SDK. After uninstalling PhoneGap, the Resources file started regenerating again. Another project, needed PhoneGap so I re-installed, and once again, the Android project (a different project) stopped auto-generating the R file - Build Automatically was checked, did the Clean, and restarted Eclipse - no dice. I removed PhoneGap and it was working once again. This was PhoneGap v 1.5 with the MDS 1.1 plugin for Eclipse.

Admin1

I followed the advice to install the platform build tools. Then The message

<package>/gen already exists but is not a source folder. Convert to a source folder or rename it.

appeared in the console. So I followed the advice and set "gen" as a source folder. This fixed the issue.

user_14971390

I would say "R can not be resolved" is something too general and can be misleading at times. I also had the same problem many times ago even when I first create a new project (which mean I did not mess with the code yet). Most of the time I just need to update my sdk manager (as some people have mentioned). But in my recent case, I found out that the path to my project file is too long (something like this E:\R&D\ANDROID\ANDROID BASIC\Folder 1\ Folder 2\..... \Folder n\MyProject). The folder names also contain spaces character. I thought it could be the case and indeed it's true, when I created a new project in another folder with shortest path possible, and none of the folders' names containing space character, it worked as normal.

user_25158390
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