Style guides

• https://developer.android.com/kotlin/style-guide
• https://kotlinlang.org/docs/coding-conventions.html

How to show a dependency tree

./gradlew [module:]dependencies

How to build an Android app

./gradlew assemble[buildVariant]

How to install an Android app

./gradlew install[buildVariant]

Testing

How to run a local unit test

./gradlew [module:]test[buildVariant]UnitTest

How to run an instrumented test

./gradlew [module:]connected[buildVariant]AndroidTest

Meaning of task clean in project-level build.gradle

The following custom task in the project-level build.gradle is to delete the project-level build directory when clicking the menu bar > Build > Clean Project.

task clean(type: Delete) {
    delete rootProject.buildDir
}

String

WebViewClient

How to get WebViewClient.onReceivedSslError() called

Open https://httpforever.com

How to get WebViewClient.onReceivedHttpError() called

Open https://httpstat.us/404

How to encode HTML entities

val encoded: String = "<>&'\"".htmlEncode() // &lt;&gt;&amp;&#39;&quot;

How to decode HTML entities

val decoded: String = String =
    Html.fromHtml("&lt;&gt;&amp;&#39;&quot;", Html.FROM_HTML_MODE_COMPACT).toString() // <>&'"

String.htmlEncode is a part of the Core KTX library and is syntactic sugar for TextUtils.htmlEncode .

How to convert AARRGGBB as Int to Color

val color: Color = Color.valueOf(0x11223344)

How to close DrawerLayout when the user taps the Back button

/** isOpen and close() require "androidx.drawerlayout:drawerlayout:1.1.0" or higher. */
override fun onBackPressed() {
    if (drawerLayout.isOpen) {
        drawerLayout.close()
        return
    }
    super.onBackPressed()
}

OnBackPressedDispatcher

• OnBackPressedDispatcher.hasEnabledCallbacks() returns true if both of the following are met.
  1. There is at least one callback registered with this dispatcher.
  2. Your Activity is being between onStart() and onStop() (both inclusive). If you override onStart() and/or onStop(), it is between super.onStart() and super.onStop().
  3. Even if you pass a Fragment to OnBackPressedDispatcher.addCallback(...), the Fragment's lifecycle does not affect OnBackPressedDispatcher.hasEnabledCallbacks().
• If your Activity overrides onBackPressed() but you forget to call super.onBackPressed() in it, your callback will never be called.

How to define a custom view

class MyCustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyle: Int = 0
) : View(context, attrs, defStyle) {
    init {
        context.withStyledAttributes(
            attrs,
            R.styleable.MyCustomView,
            defStyle,
            0
        ) { // simpler than Theme.obtainStyledAttributes(...)
            // ...
        }
    }
}