I'm making some modifications to the AOSP SystemUI app, and have run into a very particular problem when trying to run it on an arbitrary device: findViewById() returns null, while navigating through the its children reveals that it's really there.
I'm working with this AOSP source code and building it through lunch full-eng and make. It compiles fine, but SystemUI crashes with the IllegalArgumentException in the logic following line 337:
mRecentsContainer = (ViewGroup) findViewById(R.id.recents_container);
[...]
if (mRecentsContainer instanceof RecentsHorizontalScrollView){
[...]
} else if (mRecentsContainer instanceof RecentsVerticalScrollView){
[...]
}
else {
throw new IllegalArgumentException("missing Recents[Horizontal]ScrollView");
}
A bit of debugging reveals that mRecentsContainer is in fact null.
I considered that perhaps a layout was being inflated that didn't contain that particular view, so to check, I navigated recursively through all the view's children using getChildCount() and getChildAt(). That wasn't the case; @id/recents_container was right there, two levels deep:
> @id/recents_root (7f0e0070) [RecentsPanelView]: (2 children)
--> @id/recents_bg_protect (7f0e0071) [FrameLayout]: (2 children)
----> @id/recents_container (7f0e0072) [RecentsVerticalScrollView]: (1 children)
------> @id/recents_linear_layout (7f0e0073) [LinearLayout]: (0 children)
----> @id/recents_no_apps (7f0e0074) [FrameLayout]: (1 children)
------> [unnamed] (ffffffff) [TextView]
--> @id/recents_dismiss_button (7f0e0075) [View]
A singular hint appears in Logcat from system_process when installing the app:
12-11 22:38:01.090: W/ResourceType(165): Failure getting entry for 0x7f060000 (t=5 e=0) in package 0 (error -75)
Inspecting R.java in the SystemUI_intermediates directory reveals that it points to a seemingly unrelated status_bar_recents_app_label_color, which is simply a defined color in res/values/color.xml.
What can be causing this? Is the layout not inflating correctly because I'm running it on a device I didn't compile against? I considered that perhaps the problem may be SystemUI's references to internal Android resources, which might not map correctly to those on my device. Is that possible?
Evidently some generated files were sticking around.
Rebuilding the source from scratch through make clean resolved it.
Alternatively, I've figured out that deleting the following intermediate directories makes for a faster build, but am not 100% sure that this covers all directories:
rm -rf out/target/product/generic/obj/APPS/SystemUI_intermediates/
rm -rf out/target/common/R/com/android/systemui
rm -rf out/target/product/generic/obj/APPS/framework-res_intermediates/
rm -f /out/target/common/R/com/android/internal/R.java
rm -rf out/target/product/generic/obj/PACKAGING/
rm -f out/target/product/generic/system/app/SystemUI.apk