如何修复程序包R不存在setContentView（R.layout.activity_main）及其后果？

Question

At first the error message was :

error: package R does not exist setContentView(R.layout.activity_main);

then I read a lot of answers in the StackOverflow about this problem so I tried to check the package name in the MainActivity and also the manifest file and then imported mypackage.R, then the problem message becomes like that:

    Creating myapp-debug-unaligned.apk and signing it with a debug key...
C:\Users\m0unta\AppData\Local\Android\android-sdk\tools\ant\build.xml:960: The following error occurred while executing this line:
C:\Users\m0unta\AppData\Local\Android\android-sdk\tools\ant\build.xml:971: The following error occurred while executing this line:
C:\Users\m0unta\AppData\Local\Android\android-sdk\tools\ant\build.xml:314: 
java.lang.NoClassDefFoundError: Could not initialize class sun.security.x509.X500Name
    at com.android.sdklib.internal.build.SignedJarBuilder.writeSignatureBlock(SignedJarBuilder.java:384)
    at com.android.sdklib.internal.build.SignedJarBuilder.close(SignedJarBuilder.java:273)
    at com.android.sdklib.build.ApkBuilder.sealApk(ApkBuilder.java:795)
    at com.android.ant.ApkBuilderTask.execute(ApkBuilderTask.java:371)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.Sequential.execute(Sequential.java:68)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.MacroInstance.execute(MacroInstance.java:396)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.Sequential.execute(Sequential.java:68)
    at com.android.ant.IfElseTask.execute(IfElseTask.java:124)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.Sequential.execute(Sequential.java:68)
    at com.android.ant.IfElseTask.execute(IfElseTask.java:124)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.Sequential.execute(Sequential.java:68)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.taskdefs.MacroInstance.execute(MacroInstance.java:396)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
    at sun.reflect.GeneratedMethodAccessor269.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.Target.execute(Target.java:435)
    at org.apache.tools.ant.Target.performTasks(Target.java:456)
    at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1405)
    at org.apache.tools.ant.Project.executeTarget(Project.java:1376)
    at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    at org.apache.tools.ant.Project.executeTargets(Project.java:1260)
    at org.apache.tools.ant.module.bridge.impl.BridgeImpl.run(BridgeImpl.java:286)
    at org.apache.tools.ant.module.run.TargetExecutor.run(TargetExecutor.java:555)
    at org.netbeans.core.execution.RunClassThread.run(RunClassThread.java:153)
BUILD FAILED (total time: 2 seconds)

Note: I am using Netbeans, and not Android Studio (maybe this is the problem, I don't know )

Answer 1

R.java is generated when building your app. The first thing to do to try to solve this error is to clean and rebuild your project. If you still get the same error, then check all XML files. Errors in AndroidManifest.xml and any layout or other XML resource files will stop generation of R.java.

I strongly suggest that you switch to Android Studio since it is the officially supported IDE.

Answer 2

It's exactly like @Code-Apprentice said: I had made a new project by copying files from old project.

Tried to run: Package R does not exist .

I did Clean and Rebuild , twice; still had the error.

I swear to you that I checked every xml file - AndroidManifest, ic_launcher, activity_main, colors, dimens, strings - but saw no problem, so I ran.

Same error, of course; I'd changed nothing. Considered exiting and restarting Studio. Nah. As Rocky said to Bullwinkle who was about to try to pull a rabbit from a hat, "That trick never works." (But sometimes it does.)

So my brain finally fired up an idea: I did a global project search for the old package name and found it in 3 places, one of which I could change: in AndroidManifest.xml . I had changed one, but not the other occurrence of the old package name.

PS I had wondered why I was getting a "can't find" sort of message on this line:

    <activity android:name=".MainActivity">

I changed it to com.dslomer64.volumecontrolssbplus.MainActivity and no other error occurred at the time, but then I ran and got the "R" error. (I SHOULD have smelled a rat and looked closely right then at the rest of AndroidManifest .)

The Moral: Look closely at all xml (especially AndroidManifest ?) and then look closer and if you still don't see the problem, do a global project search for the old package name, with options "match case" and "whole word".

Answer 3

mention

import com.projectdir.subdir.R;

in your java file..

it needs proper path to access R

....mine worked after this