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F#でAndroidアプリ開発 カウンター(数取器)編

Last updated at Posted at 2020-01-03

F#でAndroidアプリ開発としてカウンター(数取器)の作成方法を紹介します.

F#でのAndroidアプリ開発の基本は以下の記事を参考にしてください.
 F#でAndroidアプリ開発 Helloworld編

ソリューションエクスプローラーのResources\layout\Main.axmlを開くと画面レイアウトが表示されます.
1_solutionExplore.png

Main.axmlにツールボックス内の"TextView"や"ImageButton"を配置します.
2_toolBox.png

Main.axml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:text="@string/cnt"
        android:layout_width="match_parent"
        android:layout_height="254.5dp"
        android:id="@+id/counterText"
        android:gravity="center"
        android:textSize="@android:dimen/app_icon_size"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <ImageButton
            android:src="@drawable/decrement"
            android:layout_width="194.0dp"
            android:layout_height="233.0dp"
            android:scaleType="centerInside"
            android:layout_weight="1"
            android:background="@null"
            android:id="@+id/imageButton1"
            android:layout_marginTop="0.0dp"
            android:layout_marginRight="0.0dp" />
        <ImageButton
            android:src="@drawable/increment"
            android:layout_width="180.0dp"
            android:layout_height="match_parent"
            android:scaleType="centerInside"
            android:layout_weight="1"
            android:background="@null"
            android:id="@+id/imageButton2"
            android:layout_marginTop="0.0dp" />
    </LinearLayout>
</LinearLayout>
android:text="@string/cnt"

また,上記箇所の参照を追記します.
Resources\values\Strings.xml下記のように編集することで,文字列を参照することができます.

Strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="cnt">0</string>
  <string name="hello">Hello World, Click Me!</string>
  <string name="app_name">TallyCnt</string>
</resources>

MainActivity.fsは以下のようにしました.
imageButton2が押されたときはカウントを+1し,
imageButton1が押されたときはカウントを-1しています.
# 事前にビルドをしておかないとエラーが起こるように見えるかもしれません.

MainActivity.fs
namespace TallyCnt

open System

open Android.App
open Android.Content
open Android.OS
open Android.Runtime
open Android.Views
open Android.Widget

type Resources = TallyCnt.Resource

[<Activity (Label = "TallyCnt", MainLauncher = true, Icon = "@mipmap/icon")>]
type MainActivity () =
    inherit Activity ()

    let mutable count:int = 1
    let mutable counter:int = 0

    override this.OnCreate (bundle) =

        base.OnCreate (bundle)

        // Set our view from the "main" layout resource
        this.SetContentView (Resources.Layout.Main)

        let cntText = this.FindViewById<TextView>(Resources.Id.counterText);
        let incrementButton = this.FindViewById<ImageButton>(Resources.Id.imageButton2);
        incrementButton.Click.Add(fun args ->
            counter <- counter + 1
            cntText.Text <- sprintf "%d" counter
        )

        let dencrementButton = this.FindViewById<ImageButton>(Resources.Id.imageButton1);
        dencrementButton.Click.Add(fun args ->
            counter <- counter - 1
            if counter < 0
            then counter <- 0;
            cntText.Text <- sprintf "%d" counter
        )

デバッグしてみると出来上がりです.
3_Screenshot.png

4_Screenshot.png

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