Google Andriod Study Jam 學習筆記(1)

2022-06-10

4 minute read

學習範圍

單元 1 ~ 單元 2 課程 2

Kotlin 語法

函式

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fun <function name> : <return type> {

}

輸出

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println("Hi") // 有換行
print("Hi") // 沒換行

宣告變數

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val <variable name> = <variable value>
val <variable name> = <class name>(parameter)

迴圈
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repeat (<times>) { }

class

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class <class name> (val <variable name>: <variable type>, ...) {
    val <variable name> = <variable type>
    fun <function name> {

    }
}

inherit

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// abstract: 未完整實作，無法執行個體化
abstract class Dwelling(private var residents: Int) {
    abstract val buildingMaterial: String
    abstract val capacity: Int

    abstract fun floorArea(): Double

    fun hasRoom(): Boolean {
        return residents < capacity
    }

    fun getRoom() {
        if (capacity > residents) {
            residents++
            println("You got a room!")
        } else {
            println("Sorry, at capacity and no rooms left.")
        }
    }

}


class SquareCabin(
    residents: Int, val length: Double) : Dwelling(residents) {
    override val buildingMaterial = "Wood"
    override val capacity = 6

    override fun floorArea(): Double {
        return length * length
    }

}

// 只有 open 跟 abstract 可以被繼承
open class RoundHut(
    val residents: Int, val radius: Double) : Dwelling(residents) {

    override val buildingMaterial = "Straw"
    override val capacity = 4

    override fun floorArea(): Double {
        return PI * radius * radius
    }

    fun calculateMaxCarpetSize(): Double {
        val diameter = 2 * radius
        return sqrt(diameter * diameter / 2)
    }

}

class RoundTower(
    residents: Int,
    radius: Double,
    val floors: Int = 2) : RoundHut(residents, radius) {

    override val buildingMaterial = "Stone"

    override val capacity = floors * 4

    override fun floorArea(): Double {
        return super.floorArea() * floors
    }
}

IntRange

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val tmp = 1..6 // tmp 是一個 type IntRange 的 variable, 範圍是 [1, 6]

when

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when (<variable>) {
    <value> -> <execute content>
}

其中 <value>可以是給定 variable

with

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with (instanceName) {
    // all operations to do with instanceName
}

搭配class的例子

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with(squareCabin) {
    println("\nSquare Cabin\n============")
    println("Capacity: ${capacity}")
    println("Material: ${buildingMaterial}")
    println("Has room? ${hasRoom()}")
}

Android Studio

UI
- TextView、ImageView、Button
- material design tool1
- material design tool2
- component

hardcode
不要 hardcode，把 text 的名稱弄到 string.xml
ex.

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<resources>
    <string name="app_name">Happy Birthday</string>
    <string name="happy_birthday_text">Happy Birthday, Sam!</string>
</resources>

text 那格就變成填 @string/happy_birthday_text

object reference (其實我不知道應該把它歸在寫 app 還是語法)
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val rollButton: Button = findViewById(R.id.button) val resultTextView: TextView = findViewById(R.id.textView) resultTextView.text = "6"
findViewById會在 layout 中找到 Button，然後把Button的 object reference 存到 rollButton 裡

顯示訊息給使用者

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val toast = Toast.makeText(this, "Dice Rolled!", Toast.LENGTH_SHORT)
toast.show()

設定貨幣（數字）規格

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val formattedTip = NumberFormat.getCurrencyInstance().format(tip)

binding

activitity_main.xml 中

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binding.tipResult.text = getString(R.string.tip_amount, formattedTip)

string.xml 中

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<string name="tip_amount">Tip Amount: %s</string>

打完字收起小鍵盤

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 private fun handleKeyEvent(view: View, keyCode: Int): Boolean {
     if (keyCode == KeyEvent.KEYCODE_ENTER) {
         // Hide the keyboard
         val inputMethodManager =
             getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
         inputMethodManager.hideSoftInputFromWindow(view.windowToken, 0)
         return true
     }
     return false
 }

螢幕轉向、不同尺寸

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 <ScrollView
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_height="match_parent"
     android:layout_width="match_parent">

     <androidx.constraintlayout.widget.ConstraintLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:padding="16dp"
         tools:context=".MainActivity">

         ...
     </ConstraintLayout>

 </ScrollView>

unittest

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@RunWith(AndroidJUnit4::class)
class CalculatorTests {

    @get:Rule()
    val activity = ActivityScenarioRule(MainActivity::class.java)

    @Test
    fun calculate_20_percent_tip() {
        onView(withId(R.id.cost_of_service_edit_text))
            .perform(typeText("50.00"))

        onView(withId(R.id.calculate_button)).perform(click())

        onView(withId(R.id.tip_result))
            .check(matches(withText(containsString("$10.00"))))
    }
}