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How to copy resources files from other directory into Android project during sync or build?

The question
When you need to use resource files, such as images, in your Android project, typically you put them in the res directory (e.g. res/drawable), and the Android build process picks them up by default. But what if your resource files come from a directory outside of your Android project? How do you copy them into a folder like res/drawable during sync or build?
What I have tried
I have a feeling that the solution is to write Gradle code, but I'm not sure how to do it. I tried the following code in my app module build.gradle file:
task copyResources(type: Copy) {
from '../../../images'
into 'res/drawable'
}
But it did not copy anything as far as I can tell. This is probably just my ignorance of how to use Gradle, and I could use some help.
I realize I could manually copy from ../../../images to res/drawable, but let's say those files change often, and I want to get the current version automatically whenever I sync or maybe whenever I build. If this is possible, I would appreciate knowing how to do it. If it is not possible, I would like to know that as well.

See How to run copy task with android studio into assets folder
Can do with adding
preBuild.dependsOn copyResources
after task copyResources(){...}
in your build.gradle.
But, it's not a good way for copying resources.

Generally you don't want to do that. The reason is that it makes what would otherwise be a clean source control system confused by the copied files.
A better idea would be to build an Android library (AAR) housed in a separate project, then consume them by adding that AAR as a dependency to the parent project.

Using a linked file in Assets directory - FileNotFound Exception

I am trying to link to an external file from a shared repository between my iOS and Android apps. This does not present a problem for iOS, but it does for Android. My current solution is to create a copy of the file from the external repository and place it in my projects Assets folder. This solution works, but is not much of a good one in my opinion and involves too many extra steps.
Using Eclipse, I am able to link to a resource. It's as simple as copying a file into my Assets folder and being prompted to either copy the file or link to the resource. If I link to the resource and try to run my app, I get a FileNotFoundException. If I copy the file instead, the app file is found just fine.
Ideally, I'd like to link to the file so that when I pull a new update from git then I don't need to copy the file over every single time. I'd prefer to link to the file.

I don't know what Eclipse uses "under the covers" for "Link here" drag-and-drop stuff. However, it is an Eclipse-ism. Android's build tools are fairly isolated from Eclipse proper, and so they won't know about those links.
Using a hardlink, or perhaps a symlink, at the OS X filesystem level should work, as both Eclipse and Android's build tools should treat it like a local file.

Are user-defined directory names allowed in an Android Eclipse project

I think I may know the answer to this question already, but I just wanna be 100% sure. Anyways, I am writing an Android app using Eclipse 4.2 ("Juno"). I want to create my SQLite database by using external files and reading/parsing these files by my code. Hence, I created my own directory called /database and placed it in my project's root directory. Then, Eclipse starts complaining, reports a problem and says:
Invalid recourse directory name.
I even tried placing my database directory in the existing /res directory, but that caused the same Eclipse problem. Just want to confirm what my initial thoughts are: Is it not allowed for me to define my own directories in the project and bundle it in with my release?
If so, then I guess I'll have to follow along with what was posted in this stackoverflow question.

put it in /assets not in /res and it should work.

You should be able to create arbitrary directories in the root of your Android project, however your application won't be able to access these files. This is useful for development purposes like storing test data, documentation, or jar files. However, you cannot create non-standard directories in places like gen and res.

Share assets among multiple projects

As we all know by now, Android's Eclipse+ADT IDE framework doesn't support (re)using assets from a Library Project.
Instead, any asset resources used by an application must be stored in the assets/ directory of the application project itself.
My problem is that I have 8 (eight!) applications using the same Library Project that uses assets and as a result of the aforementioned limitation I have to copy/duplicate and sync each of the asset files to all 8 (eight!) applications.
This is a maintenance nightmare and it is error prone, too.
Any idea how to work around this by sharing a single copy of each asset among multiple application projects?
Note: I'd like to avoid an OS or filesystem dependent solution like hardlinks or softlinks. I prefer a solution like context.getAssets(), if it indeed does the work.

Maybe things have changed since you posted the question, but I was able to reuse asset files from another project in my Android project. I created my project's assets folder as a linked folder. I posted a sample project to show how it works.

how to reference an asset in a library project

In a class belonging to a Library project I call:
webview.loadUrl("file:///android_asset/info.html", null);
Unfortunately, this only works if I duplicate the file info.html into the Application's project asset folder as well.
Is there a way to tell an Android library code: "look for this file in the library's assets folder, not in the application's assets folder" ?

This answer is out of date, the gradle build system and AAR files support assets.
From the Android Docs:
Library projects cannot include raw assets
The tools do not support the use of raw asset files (saved in the assets/ directory) in a library project. Any asset resources used by an application must be stored in the assets/ directory of the application project itself. However, resource files saved in the res/ directory are supported.
If you want to include files from a Library project, you'll need to put it in the resources instead of the assets. If you're trying to load HTML files from your library project into a WebView, this means that you'll have to go a more roundabout method than the usual asset URL. Instead you'll have to read the resource data and use something like loadData.

This is now possible using the Gradle build system.
Testing with Android Studio 0.5.0 and v0.9 of the Android Gradle plugin, I've found that files such as
MyLibProject/src/main/assets/test.html
are correctly packaged in the final application and can be accessed at runtime via the expected URL:
file:///android_asset/test.html

You can achieve this by creating a symbolic link in the project's asset folder that points to the directory in the library project.
Then you can access as below:
webview.loadUrl("file:///android_asset/folder_in_a_libary_project/info.html", null);

Okay. Ive been stressing out and losing sleep about this for a while. Im the type of person that loves API creation, and HATES complicated integration.
There arent many solutions around on the internet, so im quite proud of what Ive discovered with a bit of Eclipse Hackery.
It turns out that when you put a file in the Android Lib's /assets folder. The target apk will capture this and place it on the root of the APK archive. Thus, making general access fail.
This can be resolved by simply creating a Raw Java Library, and placing all assets in there, ie (JAVALIB)/assets/fileX.txt.
You can in turn then include this as a Java Build Path Folder Source in
Project > Properties > Java Build Path > Source > Link Source.
Link Source
Click on Variables. and Add New Variable, ie VAR_NAME_X. location : ../../(relative_path_to_assets_project)
Click Ok
Now, when you build and run your app, the assets folder in the APK will contain your (GLOBAL Library) files as you intended.
No need to reconfigure android internals or nothing. Its all capable within a few clicks of Eclipse.

I confirm that Daniel Grant's approach works for at least the following situation: target project does NOT have an asset folder (or the folder is empty, so you can safely delete it).
I did not setup any variable.
Simply setup a LinkSource as follows (just an example)
Linked folder location: /home/matthew/workspace_moonblink/assetsForAdvocacy/assets
Folder name : assets
The "assetsForAdvocacy" is a Java project, (created with New- Project - Java Project) with empty src folder, and a new folder named "assets", which now provides the entire assets folder for the target project.
This is a fairly straightforward way within Eclipse to provide assets re-use across many different projects IF they do not already have assets, good enough to get going with. I would probably want to enhance it to become a content provider in the long run, but that is a lot more development.
My project accesses the assets with the following code:
String advocacyFolderInAssets = "no_smoking/"; //a folder underneath assets/
String fn =advocacyFolderInAssets+imageFilename;
Bitmap pristineBitmapForAdvocacy = getBitmapFromAsset(context, fn);
I use Motodev Studio 3.1.0 on Ubuntu. It would not let me 'merge' a new assets folder in the new assets-only project onto an existing assets folder in the target project.

If you want to use a setup where multiple derivate products are created from one library you might consider using svn:externals or similar solution in your SCM system. This will also do the trick that static assets like online help may be versioned seperately from the android source code.

I found this older question, it might help you, too.
This is the official way Google uses to archive this (from the above post): Link