Develop Reference

Java Android Eclipse: R Classes disappear [duplicate]

http://developer.android.com/training/basics/firstapp/building-ui.html
I have been following this tutorial, but I have two errors, both "R cannot be resolved to a variable". I have made android apps (easy ones) in the past, and I remember this problem being fixed by checking whether or not I have an import R statement (which I don't) and whether or not the project has been cleaned before being built again (I cleaned it and I still get the error). I am at a loss as to what to do. Thanks!
*I also want to mention I did see the thread of the same title with 170 hits, and the solution of "delete the import R statement" does not apply to my problem (I don't think)
Thanks again
All code is straight from the link above, but here it is for convenience
activity_my_first.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal">
<EditText android:id="#+id/edit_message"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:hint="#string/edit_message" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/button_send" />
</LinearLayout>
MyFirstActivity.java
package com.example.myfirstapp;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v4.app.NavUtils;
public class MyFirstActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_first);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_my_first, menu);
return true;
}
}
strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">My First App</string>
<string name="edit_message">Enter a message</string>
<string name="button_send">Send</string>
<string name="menu_settings">Menu Settings</string>
</resources>
edit: When I clean the project, I get this message in the Console:
[2012-06-29 11:12:38 - MyFirstApp] W/ResourceType( 6140): Bad XML
block: header size 91 or total size 0 is larger than data size 0
[2012-06-29 11:12:38 - MyFirstApp]
C:\Users\zhong\workspace\eclipse\MyFirstApp\res\menu\activity_my_first.xml:2:
error: Error: No resource found that matches the given name (at
'title' with value '#string/menu_settings').
edit: added a line to layout xml file <string name="menu_settings">Menu Settings</string>
Fixed cleaning project errors, but I still can't run the project from the two R errors.

I'm working my way through the same example, and had the same (or very similar) problem.
Finally I noticed that there was a tiny little red x on the manifest.xml.
Sure enough, it was complaining about this:
android:label="#string/title_activity_hello_world" >
So I added:
<string name="title_activity_hello_world">Hello World</string>
to strings.xml and now it works.

I had the same issue while following the tutorial.
Cleaning the project or cleaning the imports did not solve the problem.
How the problem was (simply) solved : I quit Eclipse and relaunched it.

2 possible things
The package name specified in the Android Manifest isn't the same as the in the Java files.
Or, your IDE hasn't generated the R.java file in the gen/ folder. Try building again (despite the error) and it will usually clear it up.
Basically the R.java file is generated for you and in the same package so you can refer to it as simply R.

I had android:text="#string/button_send"
Which gave the error: No resource found that matches the given name (at 'text' with value '#string/button_send').
I tried to solve the error using the tuturial. But the tutorial fails to tell me to write all the lines required one by one. So I miss to write "<string name="button_send">Send</string>" in the strings.xml.
After adding the previous line the error disappear! Which I believe is something similar to the original problem in this thread.
So if I had copied the whole lines from the given tutorial it may had not happened, but by typing our-self is how I think is the best way of learning.

I found the solution:
go to your project->res->menu than open the XML file there and delete this line:
android:title="#string/menu_settings"
I deleted it and it start to work,after 3 hours of the same warning in the problem section.
It even make sense when you read it, "at title with value #string/menu_settings"

Pleas confirm there is no error in
1- Project folder
2- Problem View of eclipse
3- Console
4- error log as in image

You have to make sure to
Clean your project Project-->Clean
The /res directory doesn't contain errors (some files will show up
with a red icon on the file explorer)
Your imports doesn't contain this line import android.R;
Check that in AndroidManifest.xml, the attribute package has the
correct value. <manifestxmlns:android="http://schemas.android.com/apk/res/android"
package="your.correct.package.name"

This fixed it for me:
https://stackoverflow.com/a/3259974/1538785
Seems like eclipse likes to add an import line to java files for no reason. Go onto your java file, hit ctrl+shift+o and all the import statements will appear. Delete the line that says import andriod.R

Right click on the Project, select "Android Tools" > "Add Support Library" > "Android Support Library, revision 11" > "Install"

In my case, the problem was that I was on 64-bit Linux, and the required 32-bit libraries were not installed, meaning that the build tools could not generate R.java.
Running this command, then cleaning the project, fixed the problem:
sudo apt-get install ia32-libs

Make sure the executables (aapt etc.) in sdk/build-tools/android-xyz/* are executable if you are running the default download on your Linux box...

I had the same error trying to do the first tutorial. To get the app to run I edited MainActivity.java so it looked like this
package com.example.myfirstapp;
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}

Android Studio 2.1 Cannot resolve symbol 'R'

Android Studio 2.1,
Java V8 Update 91, Gradle 2.1.0 .
I know that this questions has been asked many times here, but none of the recommendation solutions works out.
In a sudden after compiling ready to run on Emulator, my IDE give an error at the R.id attribute. Every Java files suddenly give the same error even I don't make any changes to the file.
I tried to make a new project, see if things different but the error keep coming. In my mind it could be internal error, again. Even I just update my IDE just now.
The Java file;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_science);
list_View = (ListView) findViewById(R.id.maintable);
String[] Days = new String[] { "Sunday", "Monday", "Tuesday", "Wednesday","Thursday", "Friday", "Saturday"};
dayList.addAll(Arrays.asList(Days));
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, dayList);
list_View.setAdapter(adapter);
NfcAdapter nfc = NfcAdapter.getDefaultAdapter(this);
if (nfc.isEnabled()) {
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, dayList);
Toast.makeText(this, "NFC turned ON", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(this, "Please turn On NFC", Toast.LENGTH_SHORT).show();
}
}
The R is the error.
XML file that associate to the Java;
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/maintable"
>
</ListView>
Is this, again, an internal error?

Try syncing the project, go to Tools > Android > Sync Project with Gradle Files
UPDATE
If you're using Android Studio 3.3, use the Sync Project with Gradle Files icon

I have just gone through this nightmare. Ended up removing all xml code to notepad until it was fixed. Then reintroduced sections of code until problem appeared.
Thinking back, it all started when I pasted some code using WordPad. Apparently WordPad contains a different coding or something so bet to avoid.
Anyway just check your white space in xml by deleting it all to rid yourself of any hidden characters.

Try performing a clean and rebuild by going to Build > Clean Project and Build > Make Project

Sometimes the R.java class is not created when there is some error into an xml file (like activity_main.xml). For example, if you change some attribute name that has a reserved word that cannot be changed.
Like this: if you changed the attribute called: id to another name like
id_A_Word_With_Error_Here in this code that can be part of the activity_main.xml, your error (R class not created) can occur.
<android.support.v7.widget.RecyclerView
android:id="#+id/messageRecyclerView"
and there is an error like:
<android.support.v7.widget.RecyclerView
android:id_A_Word_With_Error_Here="#+id/messageRecyclerView"
If clean, rebuild did not work and there is no error with import like import com.something... , my suggestion is to search an error into xml files.

I've seen this problem many times. The right solution is:
When you type R, the Android Studio will give you many different namespaces for R to choose from, that look like R(***.***.***), but what you really need is the namespace that ends with ***.myProject. (Note: myProject is your project name), e.g: R(com.example.milka.demoProject).
If you choose any other namespace, you will get the error message, so you have to delete the unneeded import, and re-choose your R

I try to change the Gradle version from 2.1.0 to 2.0.0, even in AS ver 2.1, ignoring the Instant Run performance and its work out. The little R error is now gone. Now, I tried to change back to 2.1.0, the R error also gone..!!
Sometime this little thing drive me crazy, a bit.
Shame on me.

Maybe the error may cause for the tools, trying install Android SDK Build Tools from Tools > Android > SDK Manager.
or maybe this error can be caused by adding an activity to a namespace that is different to the root, you can trying >>Import com.example.MyApplication.R;
or your also can clean o rebuild your project in Build > Clean Project or Build > Rebuild Project

If you are using google play services and your compilesdk version is lower than 23 then download the new sdk and update your compile version. After that try cleaning and rebuilding. It will be fixed

Have you tried Rebuild Project go to
Build> Rebuild Project
and perform it without doing the Clean project
I had the same problem & it worked for me

R cannot be resolved to a variable, usual fix doesn't seem to work

I am trying to compile my android app that I am crating by following the google tutorial at https://developer.android.com/training/index.html
I have run into a problem where I get the error "R cannot be resolved to a variable"
I followed the suggestions from the other threads such as cleaning/rebuiding, removing all import android.R, and reinstalling my Android SDK Build-tools for every version
Here is a copy of the tutorial project with the issue MyFirstApp.zip
I have taken the suggestions found in other threads, but their solutions have been unsuccessful.1 2 3 4 Please help!
Please let me know if there is any other information you need to fix this issue.

I have seen your code there is an error inside main_activity_actions.xml which is inside your menu folder
It does not find #string/action_search which must be present in strings.xml
So put <string name="action_search">Search here</string> inside your strings.xml
and clean and build the project.
I hope the error will be solved.

It usually append when you have an error with your XML file.
Maybe you try to use an XML variable who doesn't exist anymore. It will not give you any error on your XML.
Verify your XML variable on your file 'Value' and which you call from your Java file

ClassNotFoundException: previously working Android Project

I had a working android project but needed to start from scratch. I copied all my source files and layout files over. There are no compilation errors but when I try to run, I get the following error.
11-27 17:21:56.793: E/AndroidRuntime(1450): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{projects.mobile.mapappproject/projects.mobile.mapappproject.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "projects.mobile.mapappproject.MainActivity" on path: /data/app/projects.mobile.mapappproject-1.apk
I am running eclipse juno and trying to run on Android 4.2. Thanks !

Rather than doing copy paste try following
1.Create an android application project
2.Delete the files which was created Eg.MainActivity and layout.
2.Right click on project name and click import ,then from File system.Go to your project directory to import the source from there
3.select that, then finish.
4.Clean and build then run

Try these
Add the Activity to AndroidManifest.xml
Is there a difference in your folder names ? For example projects.mobile.mapappproject-1 or projects.mobile.mapappproject !

I copied all my source files and layout files over.
It looks like you forgot to copy over the entries that existed in AndroidManifest.xml, however. Each Activity has an entry there and that entry is required for the framework to find and launch the UI.

I had the same problem, but I found out that a library reference path wasn't right. After I fixed that everything worked fine.
You can check this at Right-click on your project => Properties => Android -> (Library)

Just for the record in case I can help someone :
I had a project that somehow didnt work after importing it from git. I solved this by giving the name of the activity explicitly.
example:
before:
<activity android:name=".Main" [...] /> (relative)
after: <activity android:name="com.example.package.Main" [...] /> (absolute)
This may also occur if you change the manifest package and keep your relative reference (which I think is default).

In my case, following 2 steps fixed the problem
a. Setting compileSdkVersion, buildToolsVersion, targetSdkVersion to the same SDK version in build.gradle.
b. I was missing a dot in application class name in AndroidManifest.xml (Ex. android:name=".ui.ApplicationLoader")

Error: Could not find or load main class in intelliJ IDE

I'm a beginner in Java and am trying to run my code using IntelliJ that I just installed as my IDE with JDK 1.7. The following piece of code keeps does not even compile and keeps giving me the error:
Error: Could not find or load main class libTest
Code
import java.lang.Integer;
import java.lang.String;
import java.lang.System;
import java.util.*;
class book {
private String name = "trial";
private int bookCode=1;
private int issued=0;
public void Issue(){
if(issued==0) {
issued=1;
System.out.println("You have succesfully issued the book");
}
else {
System.out.println("The book is already issued. Please contact the librarian for further details");
}
}
public int checkCode() {
return bookCode;
}
String readName() {
return name;
}
public void setName(String newName){
name=newName;
}
public void setBookCode(int newCode){
bookCode=newCode;
}
}
class library {
private ArrayList books=new ArrayList();
public void getList(){
for(int bk:books){
String bName=books(bk).readName();
System.out.println((bk+1)+") "+bName);
}
}
}
public class libTest{
public static void main(String[] args){
library newLib= new library();
System.out.println("code working");
}
}
Is there any change that i have to make in the compiler settings?? Or is it the code.

This might help:
1) "Build" menu -> "Rebuild Project".
Sometimes Intellij doesn't rewrite the classes because they already exist, this way you ask Intellij to rewrite everything.
2) "Run" menu -> "Edit configuration" -> delete the profile -> add back the profile ("Application" if it's a Java application), choose your main class from the "Main Class" dropdown menu.
3)"Build" menu -> "Rebuild Project".

If none of the above answers worked for you, just close your IntelliJ IDE and remove the IntelliJ IDE file and folder from the root of your project:
rm -rf .idea *.iml
Then open the project with IntelliJ. It must work now.

For me the solution was to fix the output directory under project settings. Before I was using just "target" for the Project compiler output. Instead I updated it to have a full path e.g. D:\dev\sigplusjava2_68\target

I had this problem and I tried everything under the sun that I could think of and on this site.
None of my Java classes were being picked up after I pulled from a remote branch. All the classes had red Js by their names in the Project Hierarchy, not blue Cs.
In the end, I tried to follow this tutorial and a few steps in tried something not described and fixed the issue:
https://www.jetbrains.com/help/idea/creating-and-managing-modules.html
Here's what I did:
Goto File | Project Structure, or press Crtl+Shift+Alt+S
Select Modules under the Project Settings section.
In the Sources tab click Sources on the 'Mark as:' line.
Click the Apply button.
For some reason, all my classes then had blue C's.
Someone with a better understanding of how IntelliJ and/or IDE's might be able to explain the phenomenon, but all I know is now it can see all the classes and more importantly the main one, and run.

Invalidate cache and restart your IntelliJ, it worked for me.

Explicitly creating an out folder and then setting the output path to C:\Users\USERNAME\IdeaProjects\PROJECTNAME\out
seemed to work for me when just out, and expecting IntelliJ to make the folder wouldn't.
Also try having IntelliJ make you a new run configuration:
Find the previous one by clicking
then remove it
and hit okay.
Now, (IMPORTANT STEP) open the class containing your main method. This is probably easiest done by clicking on the class name in the left-hand side Project Pane.
Give 'er a Alt + Shift + F10 and you should get a
Now hit Enter!!
Tadah??
(Did it work?)

File > Project Structure > Modules > Mark "src" folder as sources.
This should fix the problem. Also check latest language is selected so that you don't have to change code or do any config changes.

I know this was asked a while ago, but I was just stumbling over this issue and thought my findings might help others. As pointed out, the error message is basically a result of the out folder. That's because, when you're trying to run the program, it compiles the code first, and puts the compiled result to the out location, and then it tries to load the compiled code from the out location. If the compiled code is not in the location expected, you'll get the error.
The point I'm particularly wanting to share is that some times, the code is not compiled (built), even though your run configuration specifies "Build" in the "Before launch" section of the configuration panel.
When can this happen?
One situation that can cause this to happen is if you're using modules and you manually delete the module out directory. For example, if I have a module named "foo", there should be a directory named foo under out/production. If you manually delete it, the build system may not know that it needs to be rebuilt.
Even worse, if you select Build | Build module 'foo', it still may not rebuild the module. If that's the case, you should select a file in the module, for example 'bar.java' and then select Build | Recompile 'bar.java'. Now the out directory out/production/foo should be restored.
Since IntelliJ typically knows about any changes going on, this surprised me, and took me a little time to figure out, so I thought I'd share.

Check your class module : I have encountered this problem with intellij :
I have a maven multi-module project, the problem is that i runing a class which not exist the module within the configuration, so my problem is fixed by setting the right module ("edit configuration" -> "use class of module")
may this help you

I had to mark the "src" folder as "Sources". After restarting IntelliJ and rebuilding the project I could run the project without further issues (see screenshot).
Edit: You can access the "Project Structure" tab via File->Project Structure or by pressing Ctrl+Shift+Alt+S.

I ran into this problem when my Java class was under src/main/kotlin. After I moved it to src/main/java, the problem was gone.

I have faced such problems when the class is in the default folder, i.e. when the class does not declare a package.
So I guess using a package statement (eg. package org.me.mypackage;) on top of the class should fix it.

Open Modules Tab (Press Ctrl+Shift+Alt+S). I had two modules under one project. I've solved the problem after removing the second redundant module (see screenshot).

After creating your project in intelliJ, try running the following command:
mvn package

I have tried all the hacks suggested here - to no avail. At the end I have simply created a new Maven application and manually copied into it - one by one - the pom.xml and the java files and resources. It all works now. I am new to IntelliJ and totally unimpressed but how easy it is to get it into an unstable state.

Invalidating cache didn't work.
I edited the main class java file with a dummy change and ran it. It worked.

In my case the problem seemed to be related to upgrading IntelliJ. When I did this I overwrote the files from the old IntelliJ with the files from the new IntelliJ (2017 community to 2018 community). After that all of my projects were broken. I tried everything in this thread and none of them worked. I tried upgrading gradle to the latest version (4 to 4.8) and that didn't work. The only thing that worked for me was deleting the entire IntelliJ folder and reinstalling it. All of my projects worked after that.

I have tried almost everything suggested in the answers here, but nothing worked for me.
After an hour of just trying to run my application, I noticed that my project's path included non-ASCII characters (Arabic characters). After I moved my project to a path with no non-ASCII characters, it executed just fine.

Goto File-> Invalidate Caches and Restart .
Else delete rm -rf .idea *.iml
and restart InteliJ

You can run the maven command on the pom.xml file in your project directory:
mvn clean install

For me - i tried few of the options above, did not work. Then i just renamed my Application class and that probably forced intelliJ to build a fresh jar and error message started to change. Then i renamed it back and it worked.

Mark the directory as a source directory. Opened via Ctrl+Shift+Alt+S

modules.xml with wrong content, I don't know what's matter with my IDEA.

I inherited a bunch of .JAVA files from elsewhere and couldn't figure out how to get them to work in any IDE. Ultimately I had to go to the command line where the Main.JAVA file was and run javac Main.java. This created a bunch of .CLASS files. The IDE's were then able to figure out what to do.

I got this error when using Scala/SBT. IntelliJ could not find the main class, even though everything was set up correctly.
My solution: delete the <user>/.sbt/<version>/plugins/target folder, then restart IntelliJ.

You probably would have specified a wrong package and the package hierarchy would not be right. Look below
The ide would highlight the wrong path in that case.

I'm using IntelliJ with Spring and my main class is wrapped in a JAR.
I had to mark the 'Include dependencies with "Provided" scope' in the Run/Debug configuration dialog

We are at File/Project Structure..
Answer might be:
Folder indicated as "content root" needs a child folder where the code is.
Plus find the button that marks code as excluded and not.
Not to be confused with tickbox that states excluded without telling in what phase and what**
Is it compiler exclude or runtime exclude? You are doomed to test and lot.
So no that tickbox but icons and colors.
As an idea we need to crack how it was originally thought to work. They never got it to work in first place and started add things in premature codaculation style.
It has been so many years and you cannot expect any improvement.
But as cure we can hack out some way to get it right every time.

Another thing you can check here is the actual command that is being passed to the JVM and make sure it looks OK. Scroll to the top of your Run console, it should be the first line.
Spaces in your Run Configuration VM Options field will malform the app startup command and can result in this error message
-DsomeArgument="arg with space must be quoted"

I am working with Kotlin but am guessing the problem is the same. I would start a project, create a single file and add main to it and the IDE couldn't find the main.
I tried the things in this list and none worked. I finally mentioned my frustration on one of the IntelliJ pages and was contacted. Of course, it worked fine for IntelliJ. After a couple of days back and forth, I noticed that the highlight function wasn't working and mentioned that. It turned out something was wrong with the IDE settings. I still don't know specifically what was wrong but the fix in my case was to reset the IDE settings. File->Manage IDE Settings->Restore Default settings.
After this, the green triangle start icon became visible to the left of my main function and things continued to work normally for subsequent projects.
Thanks to Konstantin at JetBrain's support for his patience.