Develop Reference

What is the correct way to add an Android Library to an Android Project?

I am trying to add android-support-v7-appcompat to my newly created Android project.
Following the Support Library Setup Documentation (developer.android.com/tools/support-library/setup.html), section Adding libraries with resources, I have created an android-support-v7-appcompat project, before adding it as an Android dependency.
EDIT: Here are more details on the process I followed to add the library project as an Android Dependency to the main project:
In the Project Explorer, right-click your project and select Properties.
In the category panel on the left side of the dialog, select Android.
In the Library pane, click the Add button.
Select the library project and click OK.
However, even if the dependency is correctly recognized, Eclipse still sees the compatibility references, such as ActionBarActivity, as errors, forbidding me to build the project. (See picture here).
To solve this problem, I tried the solutions accepted by similar questions on SE, i.e. adding android-support-v7-appcompat to the Project's Build Path, which successfully silents the errors that prevented me to compile earlier.
However, now when building and deploying the project, I get an error: the app crashes at launch, and the Console displays an error message: Could not find android-support-v7-appcompat.apk! (See picture here).
To resume, with the first configuration I am not able to compile with Eclipse, while with the second configuration I can't launch the application.
Therefore, I have two questions:
First, how should I be adding a library to my project, so I can at the same time build my project and be able to use the library's additions in my code in Eclipse?
Secondly, I feel like I am missing theoretical knowledge on how Eclipse handles dependencies.
What is the difference between adding a library as Android dependency vs Java Dependency / vs adding the project or its jar to the Build path?

First, how should I be adding a library to my project, so I can at the same time build my project and be able to use the library's additions in my code in Eclipse?
Your first approach should be fine, which would indicate that there is some other problem. For example, there may be errors in the appcompat library project that are preventing it from being compiled. However, given the error from the second approach, either you are running the appcompat library (which will not work) or something else is more fundamentally broken in your project setup, where your app thinks that it is supposed to build android-support-v7-appcompat.apk, when there is no such APK.
What is the difference between adding a library as Android dependency vs Java Dependency / vs adding the project or its jar to the Build path?
Never manually modify the build path in Eclipse for an Android project. While that will satisfy the compiler, the contents of the JAR(s) will not be packaged into your APK for use at runtime, resulting in runtime crashes (e.g., VerifyError).
"Java dependency" is for pure Java source code. Not only do you not have the source code to appcompat from the SDK, but an Android library project includes Android resources (and, at least on Android Studio, also assets and an optional manifest file).
For Eclipse, library projects are attached via the approach you describe as the first approach in your question. For Eclipse, plain JARs are just dropped into libs/ in your project root, and those are automatically added to your compile-time and runtime classpaths.

Unable to Debug Library Projects with ADT v14 - Source Not Found

Ever since upgrading my current projects to use the new R14 Tools in Eclipse, I'm now unable to debug any code that exists in my library projects.
When I hit a break point in my library project code, instead of Eclipse opening the original source file, it opens up the read-only copy of the source file contained within the JAR with the message "Source not found".
I've searched around for a solution to this, but have yet to come across anything. Does anybody else have any suggestions? It's quite a pain not being able to debug.
EDIT
The issue has came back and I'm no longer able to debug. I haven't changed any project settings around or anything. Very frustrating.

Tried all of the above and it did not work for me, however the workaround detailed here did.
http://code.google.com/p/android/issues/detail?id=20731
Start debugging, and run until you hit a breakpoint (and precisely get a .class file instead of the .java you would like to have)
Right click in the Debug view of the Debug perspective (for example on the call stack), and choose "Edit Source Lookup Path"
Add all your projects above "Default", via "Add..." > "Java project" > "Select All"
(I'm using ADT 15.0.2 preview from http://tools.android.com/download)

After having this issue as well and doing a little research, I came across this thread and another one that tipped me off. I was pulling my hair out already.
It turns out that the problem is with the build order of your projects (mine was anyway). Since ADT/SDK v14 changed the way library projects are referenced, the build order needs to be correct. Make sure all of the libraries your app uses are built first. I just moved the "src" and "gen" folders for each of my projects to the bottom and now it builds the library first and I am able to debug it and view the source of my library files through the main project.
In case someone doesn't know where to do this, in Eclipse, right click on your project and "Build Path" and then click "Configure Build Path". Then, on the "Order and Export" tab, move the two folders for your project to the bottom of the list below your libraries. I did this for all of my projects and the library projects.
You can also do it globally in Eclipse from Windows->Preferences->General->Workspace->Build Order and moving your library projects to the top. I think the build order defined in each project will override this though, so you may want to do it in both places to solve the issue now and for future projects.

I had the same problem in a project today. The project consists of an app which has two library dependencies. I could not see code during debugging and when using auto-completion when overriding methods Eclipse was unable to deduce proper argument names.
First of all, the problem manifested itself by showing the the 'gen' folder was used as the one that contained the source. To check whether this is the same issue go to your app project, open the Android dependencies and have a look at the properties of the your library dependencies. Location path said /libraryprojectname/gen.
If this is also your problem then go to the 'Order and Export' tab of each library project and move the 'gen' item below the 'src' item. As soon as you click OK Eclipse will work a bit and when you check the Android dependency properties the location path should say: /libraryprojectname/src. Open click the dependency and open any class inside the jar. It should show the source.
I am using ADT plugin 20.0.3 with Android SDK Tools 20.0.3 and Android SDK Platform Tools 14.

The following worked for me on Eclipse Juno:
In Project Properties/Java Build Path:
In the Projects tab, added my library projects.
In the Order and Export tab, moved my library projects to the top, and checked them
Not sure if it's relevant, but Android SDK tools is rev 20.0.3 and Android SDK platform tools is 14.

I assume you are opeining library project and there you put brakepoint.
Try this: On main project open Library Projects->[yourlibrary.jar]->[yourfile.class] from Package Explorer, and then in .class file put brakepoints.
This works for me at least :)

Sometimes this happens to me. Not sure about the reason but the way I solve is:
Remove the main project from eclipse. -- Closs Eclipse -- Delete the jar file in the library project -- Open Eclipse -- Wait for the library project to compile -- Import the main project

This problem also occurs with release 21 of ADT inside Juno. As a workaround, in the "debug" view of the debug perspective (where you see threads and method invocation traces), right click and edit source lookup path.

Cannot build library dependent project after update to ADT 14

In order to implement different versions of our UI we broke our program up into UI specific code and a common library project that has everything else. Up until yesterday when I updated to ADT 14 everything was working fine. Now I can't build. I keep getting the error "The container 'Library Projects' references non existing library 'path to the bin folder of my common project and the name of the project.jar'
I've been all over the web and tried everything I can think of to fix this to no avail. Can someone help me out? I'm basically stuck at this point.

Maybe you have the same issues I had when switching to the new ADT:
In my previous setup I had some resources split between the library and the main project. The library project would not compile error free on its own but only in combination with the main project which added the missing resources.
It doesn't work like this any more.
The library project must compile completely error free now. When it does the build process will create a <lib_project_name>.jar in the bin folder of the library project.
If the jar file is not created ( thus the build process of the library project failed for some reason - eg. because the changes in the R.java file (see http://tools.android.com/recent/buildchangesinrevision14 )) you will get the error message you described.
Also, I had to manually remove the <lib_project>_src from the project.

I've had a problem with a few different projects where I did the fixes suggested in the other answer, but they were only fixed temporarily.
Every time I reopened Eclipse or did a Clean on a project, the "Library Projects" directory would disappear, and I would have to open the project properties, remove the library, and add it again.
I solved this the hard way by creating a new project and copying everything into it.
Then I found an easy way to solve it. Right click the project, Refactor-->Rename. You can rename it back afterwards. This fixed it.

Check out the article "Changes to Library Projects in Android SDK Tools, r14" ( http://android-developers.blogspot.com/2011/10/changes-to-library-projects-in-android.html ) on the Android Developers blog.
E.g. #P.Melch: "I had to manually remove the _src from the project" should be done as follows:
To fix the project, you must remove the extraneous source folders with the following steps:
Right click source folder and choose Build Path > Remove from Build
path.
A dialog will pop up. In it, make sure to check “Also unlink the folder from the project” to completely remove the folder.

You have to update the Android SDK in Android SDK Manager
Android SDK Tools Intalled
Android SDK Plataforms Installed
Android SDK Builds Installed

Problems building Android project after Eclipse and SDK update

I have just updated Eclipse, the Android SDK, and everything else that appeared updatable, via Eclipse's Help->Check for Updates and Window->Android SDK Manager.
My project consists of a main project and 2 library projects. One library project is the normal Android License library project. The other library project contains Java files that reference Android resources that it itself doesn't contain, but that are present in the main project (for example R.id.myPic is used in the library project, but is actually contained in the main project). I had no problem building and running the main project before the update.
For some reason now I cannot build the main project. The main project folder has a "subfolder" called "Library Projects", which contains a jar file for the Android Licensing, but does not show a jar for the second library project. I also have a red exclamation mark on the main project folder.
For some reason I cannot rebuild the library file together with the main project. I've tried Cleaning all projects, building one then the other, building all, restarting Eclipse, but no luck.
If I go to the project properties, then Java Build Path, then Libraries, it appears that the jar file for the library project is missing, but I cannot independently create a jar file for this since it uses resources from the main project.
This is what my problems tab says:
The container 'Library Projects' references non existing library 'C:\AndroidDev\workspace\FlashcardsCommon\bin\flashcardscommon.jar'
Type: Build Path Problem
Any ideas?
Thanks a lot!

See this thread:
http://code.google.com/p/android/issues/detail?id=21031
It generally helps to go to Window -> Preferences -> General ->
Workspace and check "Refresh automatically". Then try clean
building your projects incrementally.
You may also have to remove the source inclusions that represented
your library dependencies manually. You will find that ADT 14 and
15 are very frustrating to work with when you have library projects.
It requires frequent manual cleans of libraries AND their dependent
projects to make changes to library projects effective.
Altogether, good effort by Google, but it's a bit buggy.
Another similar thread:
Cannot build library dependent project after update to ADT 14

In eclipse, unable to reference an android library project in another android project

As I was writing up this question I managed to solve it so repeat it here for the benefit of others. Here is the initial problem:
I have created a very simple library project which I want to reference in another project. I have done this previously with no problems so not really sure why it is not working this time. I have:
Flagged the library project via project properties. The default.properties file has this set : android.library=true
In my other project added reference to my library project via project properties. The default.properties file has the reference added as expected ie android.library.reference.1=K:/android_test_ws/applicationRegistrar
The green tick against the referenced library project starts off green and then changes to a red cross.
This implies that there must be something wrong / missing from the library project but I don't know what. My library project on this occasion is MUCH simpler than the previous one I created.

OK Here is the solution which I found when I was looking for the default.properies file of the referencing project (not the library) in my file system. Although the referencing project was in the same eclipse workspace as the library project, the actual files were somewhere else in the file system ie they were'nt in the same parent folder of the library project. As soon as I placed the referencing project in the same physical folder as the library project it all went fine.
I guess that this must be something to do with android using ant underneath the covers.
Edit: The project name needs match the folder name on the file system. What you are seeing in the Project Properties->Android->Library Reference is a relative file system path.

Make Sure both the projects are present in same work space.
To Do it, while importing the projects make sure "copy project into work space" check box is checked.

the same problem will occur if your library project is in different partition from your current workspace. I have the same problem just now. My git source is in C: and I just move my workspace to D: and everything start to collapse.

Simplest way to get the library paths paths correct is to use the GUI from Eclipse to add the library as shown in the following screenshot and let Eclipse take care of putting the correct relative paths in project.properties. Its a common setup to have your library projects hosted at directories vastly different than your main projects that uses the library. This method will work if the "libary project" and the project using it are in the same eclipse "workspace" (they "need not" be in same parent folder):

Please ensure that the library project is marked as "Is Library" - right click on the library project - properties - Android - mark the "Is Library" checkbox - in project.properties of the library project you should have a new entry:"android.library=true. Now add it into the project you want as described in the post below.(the post with image integrated - from Nilesh Pawar).

This bug is referenced several times here 27199, 35786, 36460 & 38052
Maybe by voting for them, it will be fixed one day...

Yet another observation on the same issue.
For me the two projects where on the same parent folder, and were both local inside the workspace. Even then the issue was still happening.
The I edited the "project.properties" file and put the absolute path(with forward slashes '/' for seperator) of the library project. Saved and closed it. Then went to the project properties dialog, removed the library(which was still showing the cross icon but with abs path) and added it back as usual.
Surprisingly the issue is resolved, and the project compiles and runs.
This is really strange and must be a bug with the ADT.
I am using ADT version 20.0.2

when developer referencing the facebook or any other library project then first of all clean the project from eclipse->project->clean project.
that want allow the error of red cross in referencing screen.

For me, I just restart the eclipse and the added library works fine.
I mean first time it showing red marks after adding the library project.
Though eclipse main project and library project are in same workspace folder and no resources files are in outside of the project folder.
So, you can try with to restart your eclipse. Happy coding....

Workaround for me was to
Create a new workspace
Import Library Project in that workspace
Import The desired project in that workspace
Having both project and library project the same target Android OS version
Reference library project in my project
solved my problem

i had the same problem there when i try to change my workspace so this my solution:
import and copy all project data including library project into workspace
delete the old project reference by Right-click on the project-->Properties-->Android-->Library, and select corrupted library(so that waht i call it) and choose Remove
clean project first (to refresh ur project properties)
go to library project Properties-->Android-->Library and check the is library if it does'nt click Apply then OK
if the library project is library is already checked, first Unchecked it then Clean the library project after that do the Step 4 again
go to project that u want the library are in then Right-click on the project-->Properties-->Android-->Library, Add then choose the library project (it should be there) and click Apply then OK
if still doesn't appear clean the project once more time and that should do

Just restart your eclipse. It's solve my problem

When you have a look at the reference-path before and after, it comes from i.e. "C:/workspace/mylib" and goes to "../../mylib" when copied to the correct location, quite interesting.

FYI,
What worked for me was to delete the 'library' projects (the actual projects) from my workspace (without deleting the files), and then re-importing them using the wizard (import existing android project from source code).

Thanks for posting the question.
I had exactly the same problem while integrating Facebook with my Android application. I fixed the issue by moving my development project to the same Windows drive in which library project was located. Somehow Eclipse is unable to read the library project's location properly from default.properties file if it is in a different drive.

Similar to Sufi Khan's post I also solved this issue with a reboot. My case differed in that when I first accessed Properties->Android and added the library I got a lovely green checkmark. When I closed the dialog Eclipse was still showing class-not-found type errors. When I checked the properties again I saw the red X. But Mr. Kahn's solution (delete the bad lib, restart Eclipse, add the lib again) worked fine.
I'm using the 0702 version of the ADT bundle (starts with "cluster", rhymes with "duck").

I followed the accepted answer but also had to make sure my "project.properties" file was readable.
If the file is readonly (checked into source control) eclipse will not edit it. Adding the library reference will succeed, but the change won't be persisted after hitting OK.
If closing the preferences window and reopening in again removes the library you just added, this may be your solution.

In case your library project still doesn't show up try adding library flag in your library project properties
Add android.library=true
project.properties
# This file is automatically generated by Android Tools.
# Do not modify this file -- YOUR CHANGES WILL BE ERASED!
#
# This file must be checked in Version Control Systems.
#
# To customize properties used by the Ant build system edit
# "ant.properties", and override values to adapt the script to your
# project structure.
#
# To enable ProGuard to shrink and obfuscate your code, uncomment this (available properties: sdk.dir, user.home):
#proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt
# Project target.
target=android-17
android.library=true