Packaging Android resource files within a distributable Jar file

Question

I am working on some reusable Android code that I would like to distribute to other developers for use within their own applications. The code has some resource dependencies (layouts, xml & png drawables) that I would like to be able to include and reference within a single package (Jar file).

Is this possible, and if so what is the best method to do this?

Answer 1

I don't have any optimistic news for you. In general you cannot distribute your own package as easily as you would expect. The main problem is the autogenerated R file. You probably make some references to it - you have your layouts and drawables. User of your library will have his own R file - containing ids for his resources, not for the ones your library provides.

In case of drawable resources you could read them in classic way, without R file. But as far as I know you are not able to inflate layouts from external xml files.

So the ugly hack here would be to distribute your library together with all your resources, which user would have to copy to his "res" folder. To be honest, there is no good solution to your problem... sorry. Regards!

Answer 2

Since Android makes the R class automatically with resource files under the /res folder, using the R class as final static is impossible.

I found a nice solution to use a jar file with the res files. Here is how I did it:

1. In your source code which will be exported in the jar file, don't use R variable because it will be replaced with a final static memory address in compile time. Instead of using R, I made my own method below:

   public static int getResourceIdByName(String packageName, String className, String name) {
       Class r = null;
       int id = 0;
       try {
           r = Class.forName(packageName + ".R");
   
           Class[] classes = r.getClasses();
           Class desireClass = null;
   
           for (int i = 0; i < classes.length; i++) {
               if (classes[i].getName().split("\\$")[1].equals(className)) {
                   desireClass = classes[i];
   
                   break;
               }
           }
   
           if (desireClass != null) {
               id = desireClass.getField(name).getInt(desireClass);
           }
   
       } catch (ClassNotFoundException e) {
           e.printStackTrace();
       } catch (IllegalArgumentException e) {
           e.printStackTrace();
       } catch (SecurityException e) {
           e.printStackTrace();
       } catch (IllegalAccessException e) {
           e.printStackTrace();
       } catch (NoSuchFieldException e) {
           e.printStackTrace();
       }
   
       return id;
   }
   

   For example, if you have a layout named main.xml, you can get it by calling the method:

   int id = getResourceIdByName(context.getPackageName(), "layout", "main");
   

   If you have a string whose id is "text1", you can get it by calling method

   int id = getResourceIdByName(context.getPackageName(), "string", "text1");
   

   This method gives you your resource id at runtime. It uses the reflection API to get the status of R at runtime.

   By using this method you can avoid using the R variable.

2. Copy your res files to your target project.

3. Build.

Answer 3

---

layouts:

hard code in your java source

---

xml & png:

copy xml & png to your project src folder and package to jar, for example

copy a.png to src/com/example/test

load it as following java codes:

    InputStream is = YourClassName.class.getClassLoader().getResourceAsStream("com/example/test/a.png");
    if ( null != is )
    {
          Bitmap bmp = BitmapFactory.decodeStream(is);

Answer 4

I just found that the aapt tool in the Android SDK allows the following option:

   --non-constant-id
       Make the resources ID non constant. This is required to make an R java class
       that does not contain the final value but is used to make reusable compiled
       libraries that need to access resources.

This sounds promising, though I have not tried this so I haven't a clue if it works. I suspect this is to get around the problem addressed by @J.J.Kim's post above.

Answer 5

You can dynamically get resource id using android method.

int preferences = context.getResources().getIdentifier("preferences", "xml", context.getPackageName());

Later your resources have to be included (copied) to your new project.

Answer 6

I was using user558185 solution but here is a more simple way. If you resources is in a library project (for a Cordova Plugin for example), you can get resource with context.getResources().getIdentifier(name, className, context.getPackageName());

This happen when the library project resources R file is not generated properly and the R packageName did not match the required packageName by the library project.

The usage is the same as user558185 answer, but it use a native Android method.

Answer 7

Hi i think this is a late response but still i just what to inform about AAR

Android ARchive - this file can hold your res and manifest files, so that the other develop can just import the aar to their project and compile their code.

This way we might get Manifest merge errors, the fix for it to use replace property in your manifest and this should be checked before distribution.

Answer 8

you can use abstraction to get the R values from the implementing class (the user).

protected abstract void getMyLayoutTextBox(int myLayoutTextBox);

Then the user has to extend your class (which extends Activity), and implement this method. In your class, you just call getMyLayoutTextBox() and you'll have the correct R value supplied by the user after he implements your distributable jar.

You can read more about abstraction here.

Answer 9

If you are using Eclipse, go to project "Properties->Java Build Path". Under tab "Source", add the res folder you want to pack (e.g. res/raw).

It will add the following line into the .classpath file
<classpathentry kind="src" path="res/raw"/>

After building done, the new jar file will contain the files in res/raw/ folder. You can access them as user558185 suggested.