Resources & Tips

Code samples

These code samples are Java based Android covered during training sessions.

Error reports

Android Emulator Hypervisor Driver for AMD Processors installation failed

1. BIOS - SVM Module → Enable (reboot)

2. Windows Features - Hyper-V & Windows sandbox & Windows Hypervisor Platform → Disable (reboot)

SD card shows little memory

Open Disk management

Delete all the partitions associated with that SD (be very careful that the partitions you are deleting are associated with the SD)

After all the partitions have been deleted you will see at the bottom of the Disk management UI an allocated large partition, this will be your unformatted SD card (you may need to refresh). Right click on it, Choose New Simple Volume from the shortcut menu. Click the Next button.

Set the size of the new volume (it is preset to disk capacity). Click the Next button.

Name the new drive. Choose a name if you want.

Choose format. (NTFS, FAT32)

Click the Next button then Finish button and you are done.

Hands-on & Tutorials

Google Developers Codelabs

Provide a guided, tutorial, hands-on coding experience. Most codelabs will step you through the process of building a small application, or adding a new feature to an existing application. They cover a wide range of topics such as Android Wear, Google Compute Engine, Project Tango, and Google APIs on iOS:

https://codelabs.developers.google.com/?cat=Android

Google Developers Training

End-to-end Android development Codelab-based training courses
https://developer.android.com/courses

Knowledge base

Documentation and References

Kotlin reference

https://kotlinlang.org/docs/reference/

Kotlin Koans

https://play.kotlinlang.org/koans/overview

Terminology

🔤Vocabulary for Android Basics

Design

dp vs. sp

dp: for UI elements

sp: for text sizes

Converting dp units to pixels

px = dp * (dpi / 160)

Density qualifiers:

ldpi: Resources for low-density (ldpi) screens (~120dpi).

mdpi: Resources for medium-density (mdpi) screens (~160dpi). (This is the baseline density.)

hdpi: Resources for high-density (hdpi) screens (~240dpi).

xhdpi: Resources for extra-high-density (xhdpi) screens (~320dpi).

xxhdpi: Resources for extra-extra-high-density (xxhdpi) screens (~480dpi).

xxxhdpi: Resources for extra-extra-extra-high-density (xxxhdpi) uses (~640dpi).

nodpi: Resources for all densities. These are density-independent resources. The system does not scale resources tagged with this qualifier, regardless of the current screen's density.

tvdpi: Resources for screens somewhere between mdpi and hdpi; approximately 213dpi. This is not considered a "primary" density group. It is mostly intended for televisions and most apps shouldn't need it—providing mdpi and hdpi resources is sufficient for most apps and the system will scale them as appropriate. If you find it necessary to provide tvdpi resources, you should size them at a factor of 1.33*mdpi. For example, a 100px x 100px image for mdpi screens should be 133px x 133px for tvdpi.

Practical tips & libraries

Android

ADB

ADB location

Check to add adb location to the end of PATH of environment variables. Eg: "C:\Users\USERNAME\AppData\Local\Android\sdk\platform-tools" to path

How to Run ADB wireless

Step 1. Connect phone with USB:

adb tcpip 5555

Step 2. Disconnect phone from USB

adb connect device_ip_address

Step 3. Run scrcpy (maybe necessary to put -s "YOUR SERIAL NUMBER")

scrcpy --bit-rate 2M --max-size 800

Take screenshot/screencast from Android

Capture screenshot on mobile and save to PC:

adb shell screencap -p /sdcard/screen.png

adb pull /sdcard/screen.png ./screen.png

Capture screencast on mobile and save to PC:

adb shell screenrecord /sdcard/screen.mp4

adb pull /sdcard/screen.mp4 .

Extra:

Deleting file: adb shell rm /sdcard/screen.png

Opening file: open ./screen.png

OpenCV on Android:

Build OpenCV 4.4.0 for Android:

https://www.youtube.com/watch?v=HgN-deEeHeQ&list=PLwfJJiO20qkB7EhtRITL3znme8mIgOwID&index=9&t=2s

Advices

Qualities of great app:

Effective

Efficient

Beautiful

Accessible

App Permissions

Check app permissions. Sometimes this can cause you error when Android app does not receive any information.

Emulator skins

Procedure how to add custom emulator skin

Tools → AVD Manager (Android Virtual Device)

Create Virtual Device

New Hardware Profile

Change:
- Device Name, ex: Samsung S20 Ultra (Black)
- Screen, ex: 6.9 inch, 1440 x 3200 px
- Default Skin (...) → Choose path to unzipped folder

Finish

Select Hardware (Samsung S20 Ultra (Black)) → Next

Select a system image (Q, Android 10.0) → Next

Set AVD Name (Samsung S20 Ultra (Black)) → Finish

Emulator skin files

Galaxy S20 Ultra:

Display: 6.9 inches (~89.9% screen-to-body ratio)

Resolution: 1440 x 3200 pixels (~511 ppi density)

Color: ⚫

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/7431c6b1-e3a0-4edb-a22e-cd0c925a5034/Galaxy_S20_Ultra_Black.zip

Galaxy S20+:

Display: 6.7 inches (~90.5% screen-to-body ratio)

Resolution: 1440 x 3200 pixels (~525 ppi density)

Color: ⚫

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/9fd9a127-9679-4da2-b063-b7658db97ec8/Galaxy_S20_Plus_Black.zip

Galaxy S20:

Display: 6.2 inches (~89.5% screen-to-body ratio)

Resolution1440 x 3200 pixels (~563 ppi density)

Color: ⚫

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/bbb465b6-8f2e-4cca-a159-25d8beb8ff76/Galaxy_S20_Black.zip

USB debuging

Activate "USB Debugging" options to see the device in Android Studio

Microcontrollers

Pins: Analog | Digital

Analog pins and Digital pins serve different purpose on microcontrollers, eg. Arduino. Digital pins give you either 1 or 0, whereas analog pin values have wider range.