Wrap-up "Kotlin for Android Developers" at Udacity

# Wrap-up "Kotlin for Android Developers" at Udacity

Personally, I want to wrap-up the course to make a summary

- Link: https://www.udacity.com/course/kotlin-for-android-developers--ud888

I learned Kotlin for Android quickly with example.

I don't think this course shows all of Kotlin.

But it's effective to learn some important points and functions in Android Studio.

1. Import Kotlin plugin in the project

    - Menu > "Tools" > "Kotlin" > "Configure Kotlin in project" > "Android with Gradle"

       This function modifies gradle files to add Kotlin plugin.

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/9484b0a9e04b95242544b2a83ca656ab64476114

2. Convert Java file to Kotlin file

    - Menu > "Code" > "Convert Java File to Kotlin File"

       This function converts a Java file to a Kotlin file.

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/f61f09a603b02dcd15bd51deb78fef699fc5181a

      This case is lucky. Normally, there are some errors about

        + Nullable check

        + Lambda conversions

        + other non-standard Java features

3. Use SAM Conversions

    - SAM: Single Abstract Method

    - Methods like "View.OnClickListener.OnClick()" can be applied.

      ex) fab.setOnClickListener { startActivity(CreateActivity.get(this@MainActivity)) }

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/ad3637101c5f8458187563e43fb548a39e819f96

4. Access views directly without "findViewById()"

    - Add "kotlin-android-extensions" plugin to support this

    - Import "kotlinx.android.synthetic.~~"

        ex) import kotlinx.android.synthetic.main.activity_main.*

              You can have direct accesses the views in "R.layout.activity_main".

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/ad3637101c5f8458187563e43fb548a39e819f96

5. Convert Java's "switch" to Kotlin's "when"

    - "when" looks like "switch" without typing "case" keyword

       and supports

        + string comparison

        + "is" keyword

        + return value

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/ad3637101c5f8458187563e43fb548a39e819f96

6. Insert a method/variable in the class

    - "kotlin-android-extensions" can make extension codes simple.

       In compile time, static method/variable is inserted for this.

        ex) val Context.layoutInflater get() = LayoutInflater.from(this)

             ==> So, we can use this like this.

            val view = context.layoutInflater.inflate(R.layout.item_note, parent, false)

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/fb586664b645c847e79678b81dc4741fa2e5e2c3

7. Use "data class" instead of just "class"

    - to support automatically

        + Identity: equal()

        + Copy: copy()

        + Hash

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/47aeae37c7488b7577bc7a5713a83753ed31f534

8. Add Anko library

    - Anko library contains a lot of helpers for Android SDK.

      In this trial, we will use "doAsync()" instead of "AsyncTask"

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/ec2d1fc3a3faa520f3d3b2c71b063bfb03af5a61

9. Use "doAsync(): instead of "AsyncTask"

    - handles thread pooling and execution

        ex) doAsync { runnable.run() }

   - Result: https://github.com/ndukwon/kotlin-notepad/commit/e28010bf0514844d5455daccbd0febcf7031f5ba

10. Apply "lateinit" keyword

    - to initialize it by the time to be used

        ex) lateinit var notes: NoteDatabase

    - should not be nullable: cleaner and safer

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/e28010bf0514844d5455daccbd0febcf7031f5ba

11. Add "@JvmStatic"

    - to help Java file understand getter/setter will be generated automatically

    - more: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.jvm/-jvm-static/index.html

    - Result: https://github.com/ndukwon/kotlin-notepad/commit/e28010bf0514844d5455daccbd0febcf7031f5ba

To be updated....

Reference:

- https://www.udacity.com/course/kotlin-for-android-developers--ud888

- https://thdev.tech/kotlin/2016/08/02/Basic-Kotlin-01.html