Using of /res - only overlay.apk(s) for changing /res-elements in target.apk(s):
The rro (runtime resource overlay) - method is used for manipulating only resource-entries(elements) that should be changed at runtime, without using a complete new standalone.apk. This means we can use overlay.apk to devliver elements, that should be changed at runtime of an target.apk. Those elements could be any matching resource in the target.apk.
In example:
the systems standard Navigation Bar Height ist defined in original target '/system/framework-res.apk/res/values/dimens.xml'
To change the Navigation Bar Height-values at runtime (without having a completely new 'framework-res.apk', we can compile an overlay.apk, that holds only the xml elements we, want to have changed at runtime (after reboot of corse).
The new overlay can be named i.e. 'framework-res-overlay.apk'. This overlay.apk will be (has to be!) compiled without any code/classses! It will copiled ONLY with resources!
The AndroidManifest.xml will have to have a xml-key, that provides the packagename of the target.apk!
code of AndroidManifest.xml will look like this(!):
overlay android:targetPackage="android" android:priority="1"
See the AndroidManifest.xml of this projekt...
(The android_packagename of our smaple target '/system/framework/framework-res.apk' is 'android' on Lollipop-OS)
Now we have to place a tiny xml-file as /res/values/dimens.xml for our new overlay.apk 'framework-res.apk', that holds only the xml-key-value-pairs, which we want to change on the target apk(!):
the code for new '/res/values/dimens.xml' will look like this:
<dimen name="navigation_bar_height">96.0dip</dimen>
<dimen name="navigation_bar_height_landscape">96.0dip</dimen>
Keep in mind, that we have to use matching resource-entries, that a really existing in the target.apk!
so we define the runtime-changes for the Navigation Bar Height!
We have to compile the new overlay.apk (without any source-code-classes!), as 'framework-res-overlay.apk' i.e.
After that, we copy the new overlay.apk ('framework-res-overlay.apk') to the device into /vendor/overlay/ramework-res-overlay.apk
(If this folder doesn't exit on device we have to mkdir it of corse!)
After doing this and after reboot, the new Navigation Bar Height values will override the default values of the target.apk (/system/framework/framework-res.apk) that we had indicated by it's packagename "android" via the android:targetPackagname in our overlay's Androidmanifest.xml
Tests with compiling thee overlay.apk with aapt via command line (only) failed here - So I use eclipse for compiling the overlay.apk(s)....