android

Detailed table of android version vs api level here (note "MR1" means "maintenance release 1"):
  https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#api-level-table
Less detailed table, with user distribution stats:
  https://developer.android.com/about/dashboards/index.html
Very cool chart of distribution history here, but it's not completely up to date:
  https://en.wikipedia.org/wiki/Android_version_history

APP THEORY:
  LIFE CYCLE:
    The standard lifecycle diagram sucks!  It has no clear notion
    of what the states and transitions are.
    This basic diagram is much better:
      https://mobisynth.wordpress.com/2009/07/24/android-activity-lifecycle/
    And slightly better (more detail on what causes what)
      http://www.wilsonmar.com/android_lifecycle.htm
    Ah, this article:
      https://medium.com/google-developers/the-android-lifecycle-cheat-sheet-part-i-single-activities-e49fd3d202ab
    is excellent, once I realized:
      - The enclosing boxes in the diagrams are states
      - The colored boxes inside them are the callbacks that get called
        upon *entering* the state.
    And it goes into detail about fragments and stuff.
    Strange that there's no single state diagram though; it's implied.

    Non-obvious bits, when a top-level activity is running:
      - user hits back button (to home screen): onPause->onStop->onDestroy; process still runs and retains any static variable values
        (unless system decides to kill it).  Relaunch does onCreate->onStart->onResume.
      - user hits home button: onPause->onStop (no onDestroy! nor onCreate when user brings it back later)
        The activity object still exists and retains state.
        (unless system decides to kill it).  Relaunch does onRestart->onStart->onResume.
      - activity calls finish(): onPause->onStop->onDestroy (like back button, unlike home button)
    

  Q: can multiple instances of a given Activity class exist within a process?
  can multiple instances of a given Service class exist within a process?
  PA: see https://developer.android.com/guide/components/activities/tasks-and-back-stack.html
  that shows how there can be multiple activities existing, if they occur at multiple places in the back stack.
  Not sure if that's relevant to my apps I've been writing so far?

  Q: what's the relationship between tasks and processes?
  PA: some links:
  http://opensourceforgeeks.blogspot.com/2014/12/difference-between-running-task-and.html
  https://stackoverflow.com/questions/8148420/difference-between-running-task-and-running-process-in-android/27571575
  https://www.sitepoint.com/activities-tasks-and-intents-oh-my/

  Q: What's the point of local broadcasts?  If "local" means "within same process",
     couldn't I accomplish the same thing more easily with an actual method call?

BUILD THEORY/PRACTICE:
  Q: how do I compile/install/run from command line (not in AS)?
  PA: 
      Compile: per https://developer.android.com/studio/build/building-cmdline.html
        ./gradlew tasks
      Note that in the gradle console in AS, it says:
        Executing tasks: [:app:assembleDebug]
      So from the command line, that's:
        ./gradlew :app:assembleDebug
      The following seems to work too (not sure what the difference is)
        ./gradlew assembleDebug
      Looks like there's a task for install, too:
        ./gradlew installDebug
      (but that takes about 5 seconds, whereas the explicit commands below take about 4 seconds).
      (however, I think that's because it does the assembleDebug too, which takes 1 second to realize there's nothing to do..
      so maybe it's a win when all together.)
      Q: if there's an emulator running, it will choose that instead of the attached actual device.
         how to direct it at a particular device?

      Install/run: look at the "4:Run" tab at the bottom of AS, to see this:

         12/27 14:26:04: Launching app
         $ adb push /Users/donhatch/AndroidStudioProjects/LinearLayoutWeightsQuestionActivity/app/build/outputs/apk/debug/app-debug.apk /data/local/tmp/com.example.donhatch.linearlayoutweightsquestionactivity
         $ adb shell pm install -t -r "/data/local/tmp/com.example.donhatch.linearlayoutweightsquestionactivity"
         Success
         $ adb shell am start -n "com.example.donhatch.linearlayoutweightsquestionactivity/com.example.donhatch.linearlayoutweightsquestionactivity.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER

       If already built:
         12/27 14:24:12: Launching app
         No apk changes detected since last installation, skipping installation of /Users/donhatch/AndroidStudioProjects/LinearLayoutWeightsQuestionActivity/app/build/outputs/apk/debug/app-debug.apk
         $ adb shell am force-stop com.example.donhatch.linearlayoutweightsquestionactivity
         $ adb shell am start -n "com.example.donhatch.linearlayoutweightsquestionactivity/com.example.donhatch.linearlayoutweightsquestionactivity.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER

       Note, per https://developer.android.com/studio/build/building-cmdline.html#RunningOnDevice , can say this instead of the adb shell pm install:
         adb install -r app/build/outputs/apk/debug/app-debug.apk
       (the -r is needed to avoid error if it's already installed)
       (may be a bit faster than the two shell am/pm commands, and definitely simpler...
       and maybe it has to be the preferred way, since there's apparently no way to make `./gradlew installDebug`
       point to a particular device)
       (also ./gradlew installDebug has the disadvantage that it doesn't give a nice green OK when build is successful)

       So current preferred method is:
         ./gradlew assembleDebug && adb install -r app/build/outputs/apk/debug/app-debug.apk && adb shell am start -n "com.example.donhatch.linearlayoutweightsquestionactivity/com.example.donhatch.linearlayoutweightsquestionactivity.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER


  Q: what's the story on various versions of stuff?
  PA: At this moment:
        Android version:
        SDK/API version:
          minSdkVersion: 15
          targetSdkVersion: 26
          compileSdkVersion: 26
          buildToolsVersion (not exactly the same track but the major version is the same): 26.0.3 (now omitting per everyone's advice) (which means it takes latest?) (upgrading to 27.0.3)
        AS version: 2.3.1 (upgraded to 3.0.1)(upgraded to 3.1.1)  (About Android Studio)
        "Android plugin for gradle" version: 2.3.1 (upgraded to 3.0.1)(upgraded to 3.1.1) (in top-level build.gradle: buildscript.dependencies.classpath 'com.android.tools.build:gradle:3.1.1')
        gradle version: 4.1 (now 4.4)

  Q: how to find out / set what api version is being used, in what senses?
  PA:
     Good overview of considerations and advice here: https://developer.android.com/training/basics/supporting-devices/platforms.html

     There seem to be three different values.  (at one point there was also maxSdkVersion that defaulted
     to targetSdkVersion, but that's not recommended and pretty much defunct, per https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#max )

     The api version related settings in File->Project_Structure->Modules->app->Properties
     correspond to those in app/build.gradle,
     and submenus correspond to variables within that file.
     Updating in AS automatically updates the gradle files,
     and updating the gradle files causes AS to notice as soon as you try doing anything nontrivial,
     and it offers to sync.  Alternatively, sync using Tools->Android->Sync_Project_With_Gradle_Files.

       app/build.gradle android.compileSdkVersion
         File->Project_Structure->Modules->app->Properties->Compile_Sdk_Version->"API 25: Android 7.1.1 (Nougat)"
         Library used to compile.
         Advice is "it is strongly recommended that you always compile with the latest SDK.".
         To change it, even if the desired one hasn't been downloaded yet,
         change it in app/build.gradle and try to compile/run in AS; it will offer option to install

       app/build.gradle android.defaultConfig.minSdkVersion
         File->Project_Structure->Modules/app->Flavors->defaultConfig->Min Sdk Version->"15"
         Minimum required to be on the machine in order to install and/or run the app.


       app/build.gradle android.defaultConfig.targetSdkVersion
         File->Project_Structure->Modules/app->Flavors->defaultConfig->Target Sdk Version->"15"
         Vaguely: highest level I've tested it on and am guaranteeing it works on.
         Q: Advice is "To allow your app to take advantage of these changes and ensure that your app fits the style of each user's device, you should set the targetSdkVersion value to match the latest Android version available."  I don't understand this.

    Q: what constraints should I follow among these levels?
    A: per https://medium.com/google-developers/picking-your-compilesdkversion-minsdkversion-targetsdkversion-a098a0341ebd
       and https://stackoverflow.com/questions/24521017/android-gradle-buildtoolsversion-vs-compilesdkversion#answer-24523113 :
         minSdkVersion <= targetSdkVersion <= compileSdkVersion <= buildToolsVersion
       but ideally, more like this in steady state:
         minSdkVersion (lowest possible) <= targetSdkVersion == compileSdkVersion (latest SDK) == buildToolsVersion (maybe with minor version number difference)
       "You’ll hit the biggest audience with a low minSdkVersion and look and act the best by targeting and compiling with the latest SDK".
       (and I think compileSdkVersion should be <= buildToolsVersion and ideally ==buildToolsVersion, too, see below... but I think maybe I'm in a state where latest available compileSdkVersion is 27 but latest available buildToolsVersion is '26.0.3'? oh no wait, '27.0.1' appeared)

    Q: how does this relate to the <uses-sdk> stuff in the manifest?
    PA: hmm, https://medium.com/google-developers/picking-your-compilesdkversion-minsdkversion-targetsdkversion-a098a0341ebd seems to imply that AndroidManifest.xml is autogenerated?
        Also that if I manually put uses-sdk in manifest, it will be ignored when building with gradle.
        Okay, I experimented, and what I found:
          - both targetSdkVersion's are used, but the one in build.gradle seems to take precedence if present.
        Seems to me that means I should put it in the manifest, doesn't it?  Otherwise it won't be seen by installation filters.
    A: Ah, per:
        https://stackoverflow.com/questions/19997509/android-studio-why-are-minsdkversion-and-targetsdkversion-specified-both-in-and
       gradle puts info missing from app/src/main/AndroidManifest.xml into the final AndroidManifest.xml
       (apparently, when developing, it appears in app/build/intermediates/manifest/*/*/AndroidManifest.xml)





     Here's some explanation, but it's not exactly android studio? https://developer.xamarin.com/guides/android/application_fundamentals/understanding_android_api_levels/
     Here's some more explanation: https://developer.android.com/guide/topics/manifest/uses-sdk-element.html
       nominally it's talking about the manifest file... which may or may not be used, but the concepts are good
       and it has min,target,max   (max is mostly defunct and no one mentions it any more)

    Example of subtlety (from https://developer.android.com/training/basics/supporting-devices/platforms.html#version-codes):
      Let's say I compileSdkVersion > minSdkVersion.
      Then I might want to put a runtime condition that only
      uses a certain function when the current sdk version is >= when the function
      was introduced.
      XXX I'm unclear on the failure modes when I get it wrong

  Q: what is buildToolsVersion (e.g. '26.0.1') in app/build.gradle? (mirrors File->Project_Structure->Modules/app->Properties->Build_Tools_Version)
  A: https://stackoverflow.com/questions/24521017/android-gradle-buildtoolsversion-vs-compilesdkversion#answer-24523113
     "buildToolsVersion is the version of the compilers (aapt, dx, renderscript compiler, etc...) that you want to use. For each API level (starting with 18), there is a matching .0.0 version."
     "You can use a higher version of the build-tools than your compileSdkVersion, in order to pick up new/better compiler while not changing what you build your app against."
     per https://developer.android.com/studio/releases/build-tools.html:
     "If you're using Android plugin for Gradle 3.0.0 or higher, your project automatically uses a default version of the build tools that the plugin specifies. To use a different version of the build tools, specify it using buildToolsVersion in your module's build.gradle, as follows: ..."
     Ian lake's page recommends omitting it now, one less thing to worry about.

  Q: ok then whats the "android plugin for gradle 3.0.0 or higher"? where is that specified?
  PA: per https://developer.android.com/studio/releases/gradle-plugin.html:
     "You can specify the Android plugin for Gradle version in either the File > Project Structure > Project menu in Android Studio, or the top-level build.gradle file."
     The latter is apparently buildscript.dependencies.classpath = 'com.android.tools.build:gradle:2.3.1' for
     one of my projects currently.
     gag, and there's a correspondence between plugin version and required gradle version,
     e.g. gradle plugin version 3.0.0+ requires gradle version 4.1+.
     Actually, it seems to be correlated with the version of AS (e.g. I'm running AS 2.3.1 right now
     and it says its using android plugin for gradle 2.3.1 ... and when I try changing that to 3.0.0 it barfs).
     Per https://developer.android.com/studio/releases/gradle-plugin.html#3-0-0:
     "The Android Studio build system is based on Gradle, and the Android plugin for Gradle adds several features that are specific to building Android apps. Although the Android plugin is typically updated in lock-step with Android Studio, the plugin (and the rest of the Gradle system) can run independent of Android Studio and be updated separately."
     I don't quite get it... this is a *gradle plugin* called "android plugin for gradle"?
     Note, it seems to be getting faster and faster, per that page, so its good to keep updated to latest.

  Q: what is the meaning of the words "android plugin for gradle"?
     Is it a plugin to the android system, that helps android know about gradle?
     Or a plugin to the gradle system, that helps gradle know about android?
  A: seems like it must be the latter.

  Q: what files should I commit to git for an android studio project?
  PA: - well, googlesamples/android-DrawableTinting does it, but I think its file list is excessive.
      - https://medium.com/@jagonzalez.develop/how-manage-android-plugin-for-gradle-version-in-a-team-df66b904c6b2
        has something about managing Android Plugin for Gradle version,
        since "(almost) all AS upgrades need you to upgrade Android Plugin for Gradle version in main build.gradle file".

  A:



HOW TO DO COMMON THINGS IN ANDROID STUDIO:
  Q: ok then how do I find out what gradle version I'm using?
  A: per that same page:
     "You can specify the Gradle version in either the File > Project Structure > Project menu in Android Studio, or by editing the distributionUrl reference in the gradle/wrapper/gradle-wrapper.properties file."
     apparently I'm using:
       android plugin version 2.3.1
       gradle version 4.1

  Q: how do I update AS to latest?
  A: Android Studio -> Check for Updates...
     it says 3.0.1 is available.  downloading it.

  Q: how to keep working while updating to latest?
    https://stackoverflow.com/questions/37351996/how-to-keep-android-studio-working-while-downloading-tools
  A: press the Background button in the modal dialog!  yay!


  Q: how do I change deployment target?
  A: Do both of the following:
       - hit the Stop button if it's running
       - if "Use same device for future launches" is checked, uncheck it (at least temporarily):
           Run -> Edit configurations... -> Android App -> app -> Deployment Target Options -> Target -> uncheck "Use same device for future launches"
  Q: how do I remove a deployment target from dialog listing candidates for Run?
  A: It shows connected devices (probably no way to prevent that) and available virtual devices.
     If I want to remove an available virtual device, that would probably be done through AVD Manager: select the virtual device and Actions -> Wipe Data (I haven't tried it).

  Q: how to disable instant run when I hit Run?
  A:  Preferences -> Build, Execution, Deployment -> Instant Run -> uncheck Enable
  Q: What's my problem with Instant Run?  Can I reproduce it?

  Q: what's the relationship between Instant Run and "Apply Changes" (the button next to the Run button)?
  PA: https://stackoverflow.com/questions/43488453/run-app-vs-apply-changes-android-studio-2-3#answer-43500455
     Run used to use "Instant Run" if enabled... but now there's a separate button for it?
     But then what does the enabled switch do?  I'm confused.
     Oh, I guess it just enables/disables "apply changes".  Weird, doesn't seem very useful.

  Q: what is kotlin?
  A: see kotlin notes

  Q: how to get the kotlin reflection api?
  PA:
     This suggested answer doesn't work as advertised
         compile 'org.jetbrains.kotlin:kotlin-reflect'
    (you can tell that the error message says it's looking for bogus names like kotlin-reflect-.jar).
     But this works (for me currently since this is my version):
         compile 'org.jetbrains.kotlin:kotlin-reflect:1.2.10'
     and this does (NOTE the double quotes! doesn't work with single)
	 compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
     But then it fails later with a "com.android.dex.DexIndexOverflowException: method ID not in [0,0xffff]: 65536".
     See question about that elsewhere in this file.


  Q: how the heck do I set the icon?
  PA: various docs and stackoverflow answers say things like:
        right-click on res -> New Image Asset, and replace android:icon="@drawable/ic_launcher" with android:icon="@drawable/myicon" in app/src/main/AndroidManifest.xml
      I tried that, and it didn't work-- it didn't put anything in drawable.
      But it put stuff in various mipmap-* directories,
      so I said android:icon="@mipmap/ic_launcher" and it worked.
      BTW, api level 26 introduced a much more complicated icon creation:
      "adaptive and legacy", with foreground and background,
      that makes it hard to make the background transparent.  So I chose
      "legacy only" in asset studio, it makes it easier and creates fewer files.
      Note, I had to regenerate the asset when level 26 came,
      because the old one was missing xxxdpi files (I think).
      (XXX argh, I think it's actually that level 26 *requires* the adaptive ones)
      (XXX and it looks like when I ask for that, it creates drawable/typewriter_el_background.xml but nothing for foreground or without-_background-or-_foreground?? is that a bug?)
  Q: how do I make the icon partially transparent?
     for "legacy" icon (used by targetSdkLevel<=25), I could do it by setting
     shape type to None.  Don't know how any more.
     (TODO: read the extensive doc about adaptive icons; it should explain)


  Q: what does it mean when the Run (play) button in Android Studio has a little
     dot in its lower right?
  A: per https://stackoverflow.com/questions/40998073/android-studio-what-does-the-green-dot-mean-in-the-run-button#answer-40998217,
     it means it's running.
     Oh!  I think I neglected to set the Name (I set foreground and background layer name, that wasn't adequate)

DEVELOPMENT/DEBUGGING:
  Q: where the heck is adb?
  PA: on mac: ~/Library/Android/sdk/platform-tools/adb

  Q: how do I adb or telnet to an emulator?
     `telnet localhost 5554` or whatever says connection refused
  A: For telnet:
       Read the instructions it gives: find the auth token and say `auth <token>`.
       Or, can change the value in that file (newline or not doesn't matter)
       or clear the file so there's no authentication needed.
     For adb:

  Q: how do I get a root shell on the emulator?
  A: not sure how "adb shell" decides to be root or not, but if it's not, you can make it so by:
       adb -e root
     that restarts the daemon so subsequent `adb shell` invocations give a root shell.

  Q: How do I "tail -f" a file on the device, through adb?
     The following behaves badly (every other keystroke is ignored):
       adb shell tail -1000000 -f /storage/emulated/0/Download/ViewDebugLog | less
  A: Add `-n` to make it ignore input (wtf?)
       adb shell -n tail -1000000 -f /storage/emulated/0/Download/ViewDebugLog | less
     Or (not sure what the distinction is, since `adb help` doesn't mention exec-out):
       adb exec-out tail -1000000 -f /storage/emulated/0/Download/ViewDebugLog | less

  Q: how to get bash instead of ash (toybox) through adb?
  PA: doesn't seem to be a way that anyone knows. here's stuff about toybox here: http://landley.net/toybox/roadmap.html

  Q: how to make /system read-write on emulator?
  A:
     You have to run the emulator in a special way, otherwise remounts read-only revert after 10 seconds or so
     (and corrupts the system, I think).
        ~/Library/Android/sdk/tools/emulator @Pixel_2_XL_API_27 -writable-system
        adb -e root
        adb -e remount

  Q: how to test/exercise android's screen rotation behavior?
     Asked as:
       https://stackoverflow.com/questions/43319781/how-to-test-exercise-androids-screen-rotation-behavior
  A: First of all, not obvious, but the emulator ui lets you choose arbitrary roll/pitch/yaw:
        menu -> Virtual Sensors -> Accelerometer -> Rotate.
      Even for just selecting one of the four primary orientations, it has nicer control here
      via 4 buttons than the simple "rotate 90 degrees CCW" and "rotate 90 degrees CW".
      As for arbitrary orientations, there's
      , perhaps some clues here:
        https://stackoverflow.com/questions/3921467/how-can-i-simulate-accelerometer-in-android-emulator#answer-20361772
      Ah yes!
        telnet localhost 5554  # or whatever port it chose
          sensor list
          sensor get acceleration
            acceleration = 0:9.81:0  # if it's in initial portrait orientation
            acceleration = -9.81:0:0  # if it's rotated 90 degrees CW from initial orientation
            acceleration = 0:-9.81:0  # if it's upside down
            acceleration = 9.81:0:0  # if it's rotatated 90 degrees CCW
          sensor set acceleration -1:1:0  # to set it to rotated 45 degrees CW from initial orientation
      Is there something analogous using adb?  (Probably not, since adb doesn't really know
      it's an emulation, and this certainly wouldn't work in a non-emulation since values
      would be clobbered by the real accelerometer)

      I added an answer to my question on stackoverflow:
        https://stackoverflow.com/questions/43319781/how-to-test-exercise-androids-screen-rotation-behavior/47842549#answer-47842549


  Q: (follow-up question (aborted because it's working now??)) why doesn't android emulator screen rotate in response to accelerometer changes?

      I'd like to script a sequence of physical device orientation changes in the android emulator,
      to test the "auto-rotate screen" behavior.

      I was hoping I could do it by making the emulated accelerator perceive gravity direction changes.
      Here's what I tried (using emulator configured as "Pixel 2 XL API 27"):

          telnet localhost 5554

      - Make sure emulated device is in natural portrait orientation
      - Make sure auto-rotate-screen is on (i.e. [Settings.System.ACCELEROMETER_ROTATION](https://developer.android.com/reference/android/provider/Settings.System.html#ACCELEROMETER_ROTATION) set to 1, i.e. screen orientation should follow accelerometer).
      - Make sure home screen allows auto-rotate (long-press on home screen -> HOME SETTINGS -> Allow Home screen rotation when phone is rotated -> On)

          telnet> sensor get acceleration
              acceleration = 0:9.81:0

      - Press emulator "Rotate counterclockwise" button; observe the screen changes to landscape mode, and the accelerometer reports the new "up" direction:

          telnet> sensor get acceleration
              acceleration = 9.81:0:0

      - Press emulator "Rotate clockwise" button; observe the screen changes back to portrait mode, and "up" direction has reverted to its original value:

          telnet> sensor get acceleration
              acceleration = 0:9.81:0

      - Now try to do the counterclockwise rotation by changing the "up" direction:

          telnet> sensor set acceleration 9.81:0:0
          telnet> sensor get acceleration
              acceleration = 9.81:0:0

      - Hey! The screen changes to landscape mode!  Wtf?  I swear it wasn't doing that correctly,
        earlier today!


  Q: how can I develop stuff in the framework?  E.g. View, ViewGroup, LinearLayout
  PA: Try to follow this:
        https://kwagjj.wordpress.com/2017/08/10/using-framework-jar-in-android-studio/
      (see notes in DIARY.txt... followed all the instructions but it's still not working)
      (except, using the final dex one because it doesn't work with the INTERMEDIATE one... not sure whether that's the problem?)
  PA: maybe a good development recipe here: http://blog.udinic.com/2014/07/24/aosp-part-3-developing-efficiently/
      the key will be something like "make snod" (got it, see recipe elsewhere in this file)
  PA: Here is a very interesting post that unwraps framework from the device,
      tweaks something, then recompiles and rewraps it:
        https://blog.jhot.me/how-to-change-the-default-orientation-of-your-android-device-76724cd759b5
      It seems to be old since it talks about BOOTCLASSPATH and dex rather than art,
      but maybe still of use?  I'd like to have a similar recipe for the modern world.

  Q: how to build android sources? (aosp)
  A:  Follow https://source.android.com/setup/ -> downloading and building
    To get the repo command:
      curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
      chmod a+x ~/bin/repo
    To initialize mirror:
      mkdir repomirror  # on a case-insensitive filesystem
      cd repomirror
      repo init -u https://android.googlesource.com/mirror/manifest --mirror
      repo sync  # ends up with 185G, currently (2018/02/05)
    To make local repo from local mirror:
      mkdir repo  # on a case-insensitive filesystem
      cd repo
      repo init -u ../repomirror/platform/manifest.git
      time repo sync  # took 1h41m, 59G
    To update mirror and local repo:
      (cd repomirror && time repo sync)
      cd repo
      time repo sync  # 4m after a month or so, 43s when already up to date
    To diff:
      repo diff
      repo diff frameworks/base/core/java/android/
    To set up environment vars and aliases for builds and runs:
      . build/envsetup.sh
      lunch aosp_x86_64-eng  # or whatever
    Then:
      To build (the showcommands is optional):
        time make showcommands -j9    # 211m initially, 141m after significant sync, 133m after another sync a month or so later (oh woops! but it failed because of a typo. another 14m after that)
        time make showcommands -j9    # initial 1m15s 148G, eventually (previously) 158G
      Incremental build just framework:
        time mmm frameworks/base showcommands -j9   # 9m43s
        time mmm frameworks/base showcommands -j9   # when already build: 8s
        time mmm frameworks/base showcommands -j9   # after change: 4m22s or 2m11s
      To make system.img for emulator, based on what's built:
        time make snod -j9 # 52s
        # apparently also needs the following, to make system-qemu.img from system.img
        # (found this from make showcommands to expand the final "Create system-qemu.img" step
        time SGDISK=out/host/darwin-x86/bin/sgdisk device/generic/goldfish/tools/mk_qemu_image.sh out/target/product/generic_x86_64/system.img  # 5.5s
      So the whole command to make system-qemu.img after making a change in source is, for me:
        time (time mmm frameworks/base showcommands -j9 && time make snod -j9 && time SGDISK=out/host/darwin-x86/bin/sgdisk device/generic/goldfish/tools/mk_qemu_image.sh out/target/product/generic_x86_64/system.img); echo $'\007' # 2m56s

      To run emulator:
        emulator
          (Note, emulated session brings up notification dialog "Phone has stopped"
          shortly after starting, but click on the background and it goes away.)

        TODO: see whether the 30-second incremental update works with emulator, described on http://blog.udinic.com/2014/07/24/aosp-part-3-developing-efficiently/

  Q: how to get a screenshot?
  A: Incidentally mentioned here: https://stackoverflow.com/questions/13578416/read-binary-stdout-data-from-adb-shell
       adb shell "screencap -p > /sdcard/foo.png"
       adb pull /sdcard/foo.png
     Or, in one step, using exec-out:
       adb exec-out "screencap -p" > foo.png

  Q: what is `adb exec-out`?  There's lots of mention of it,
     but `adb help` doesn't mention it.
  A: https://stackoverflow.com/questions/13578416/read-binary-stdout-data-from-adb-shell#answer-31401447
     It doesn't use pty which mangles binary output.

  Q: What's a good way of commenting / commenting-out parts of xml files
     such as layout/activity_main.xml or AndroidManifest.xml?
     In particular, for documenting and/or commenting-out attributes.
  PA: I like to do the following:
     In the start of the top-level element:
       xmlns:ignored="dummy_identifier"
       ignored:comment="the `ignored` namespace is for notes and comments"
     In some cases, turning the ":" into an "X" works,
     but AS will complain about it (louder than it complains about the above).
     That complained can in turn be suppressed, but the suppression net
     is too wide, so there's no perfect solution :-(

TROUBLESHOOTING:
  Q: what do I do when app crashes on startup with "can't find MainActivity on classpath"
     or something?
     (may have something to do with the attempted preBuild rule to try to add custom framework.jar,
     may be a race condition)
  PA: make a nontrivial change to MainActivity.java and recompile.
     (maybe can do something to fix race condition, too?)

  Q: build fails with "com.android.dex.DexIndexOverflowException: method ID not in [0,0xffff]: 65536"
     (after I added a dependency on kotlin-reflect).
  PA: Per https://developer.android.com/studio/build/multidex.html:
     Shouldn't be a problem if minSdkVersion>=21 (multidex enabled by default).
     But mine is currently 15, so have to do something special.
     Oh wait... actually, problem went away after "clean project" and "rebuild project"... ?

  Q: Install on emulator (API 17) failed with INSTALL_FAILED_UID_CHANGED.
  A: the following works sometimes:
      adb shell
        rm -r /data/data/com.example.donhatch.linearlayoutweightsquestionactivity  # or whatever the app name is
     but sometimes it doesn't :-(
     E.g. if I have:
       minSdkVersion 15
       targetSdkVersion 18
       compile 'com.android.support:multidex:1.0.1'
     Actually had to toss out my API 17 and 18 emulator images because of this :-(
     Argh! And still doesn't work!  Even on a brand new emulator.  First "Installation failed since the device possibly has stale dexed jars that don't match the current version (dexopt error). In order to proceed, you have to uninstall the existing application.  WARNING: Uninstalling will remove the application data!  Do you want to uninstall the existing application? [Cancel] [OK}",
     then the INSTALL_FAILED_UID_CHANGED thing.

  Q: `adb -P 5554 shell` fails with:
        error: protocol fault (status 41 6e 64 72?!)
  A: 5554 isn't for adb, silly, it's for communicating with the emulator
     (which wouldn't make sense for a real device).
     Say something like this instead:
       adb shell  # if only one device connected; disconnect the real one if necessary
     Or:
       adb -P 7000 shell
        * daemon not running; starting now at tcp:7000

  Q: how to adb when more than one emulator or device?
  A:
     adb devices
       List of devices attached
       emulator-5556   device
       emulator-5554   device
       710KPLC0178312  device
     adb -s emulator-5556 shell  # or whatever
     adb -d shell  # to connect to one that's attached via usb, if there's exactly one
     adb -e shell  # to connect to one emulator, if there's exactly one

  Q: Intermittent "E AndroidRuntime: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.donhatch.linearlayoutweightsquestionactivity/com.example.donhatch.linearlayoutweightsquestionactivity.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.donhatch.linearlayoutweightsquestionactivity.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.donhatch.linearlayoutweightsquestionactivity-4vPbPMVlnm5zvxIGERf49Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.donhatch.linearlayoutweightsquestionactivity-4vPbPMVlnm5zvxIGERf49Q==/lib/arm64, /system/lib64]]"
     Workaround: tweak the source and recompile, usually it works next time
  A: I think it happens intermittently when too many methods (I ran into it when trying to use a custom framework.jar);
     and I think the following fixes it. In app/build.gradle, in android.defaultConfig:
       multiDexEnabled true

  Q: If too much logcat output at once, ADM (android device monitor) will show:
       Device disconnected: 1
     and not be able to see any more logcat messages.
  A: In a shell:
       adb reconnect
     That will make ADM say "Device disconnected" again, but then
     click on the device in the Devices pane again, and it will be reconnected.

  Q: logging too much results in losing some of it at random.  Is there a more robust logging mechanism?
  PA: check out:
        http://leaks.wanari.com/2016/06/29/logging-tools-android-developers/  (comparison of 7 android loggers)
  PA: settings gear -> System -> Developer options -> Log buffer sizes ->
        change from 256K per log buffer to 16M per log buffer

  Q: emulator won't start after upgrade to macOS High Sierra (10.13).
     Spinning beachball for a bit, then there is an icon in the bottom dock
     but no app window.
  A: https://developer.android.com/studio/known-issues.html#body-content
     But that was a red herring-- it's just that one of my emulator images
     went bad.  Deleted it and recreated it in AVD manager.

  Q: what is "turn on view attribute inspection" (in developer options)?

VIEW/LAYOUT BUGS:
  Q: Can I get control over LinearLayout's distribution of slack/shrinkage?
     https://stackoverflow.com/questions/47894003/why-isnt-linearlayout-distributing-shrinkage-in-proportion-to-weights
  A: see that post for my answer.

USER LAND:
  Q: how to switch launchers once I've installed nova launcher?
  A: either:
        home screen swipe down from top -> Settings -> Apps&notifications -> Advanced -> Default apps -> Home app
        can set it to Pixel Launcher (the default) or Nova Launcher.
     or (from nova to pixel but not back) (XXX actually pixel to nova is available in this area somehow, but I haven't experimented enough to know exactly how it decided):
        Nova Settings (either apps drawer -> Nova Settings, or long-click-on-background -> Settings)
        -> scroll down to NOVA section -> Select Default Home
  Q: in nova launcher, how to make it *not* bring up the App search (the "Search apps... frequent / recent / new/updated" thing) when I hit Home from Home screen?
  A: Nova Settings (see above) -> Gestures & Inputs -> Home button -> Change from "App search" to None
  Q: how to make home screen allow screen rotation?
  A: pixel launcher (default launcher):
        long-press on home screen -> HOME SETTINGS -> Allow Home screen rotation when phone is rotated -> On
          (note, it's disabled when system is in portrait mode, so first change system to auto-rotate mode)
     nova launcher:
       Nova Settings (see above) -> Look&Feel -> Screen orientation
         - can pick among:
           - default
           - auto-rotate  (actually means "allow either landscape or auto", i.e. allow USER_ROTATION (as set by system settings or RotationLockAdaptive, for example)
              to have effect.
           - force portrait
           - force landscape

  Q: 300-350ms delay when tapping ui buttons?
  A: oh! it was because I had triple-click-to-zoom on.
     Settings -> Accessibility -> Magnification ->
       - turn *off* "Magnify with triple-tap" !
       - turn *on* "Magnify with button".
     That adds a button to the launch bar, which is fine!

  Q: If I'm in an app, can I stack another app on top of its back stack, so that when I finally hit the back button I get back to the original?
     (Installing using adb does that, also anything I get to through the top dropdown area does it.)
     If I want to temporarily switch to another app that's *not* available that way,
     currently the quickest way I know how to do it is to hit home,
     bring up second app, then when done, go back to home and then Recents (not called that any more-- now called Overview? lame)
     to get to original running app.

  Q: can I get seconds in the clock display at the top of the screen? (not sure what the area is called)
  PA: top dropdown -> long press on settings gear to enable System UI Tuner in Settings.
      Then: Settings -> System -> System UI Tuner (last menu item) -> Status bar -> Clock -> change to "show hours, minutes, and seconds"

EXCELLENT APPS:
  - Sensor Kinetics
  - Open Camera
     


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