やりたいこと

ボタンを押すとカメラが起動する。
カメラで撮影した写真をビューに表示する。

画面

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btnLaunchCamera"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="32dp"
        android:text="カメラを起動する"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <ImageView
        android:id="@+id/cameraImage"
        android:layout_width="335dp"
        android:layout_height="336dp"
        app:layout_constraintBottom_toTopOf="@+id/btnLaunchCamera"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

</androidx.constraintlayout.widget.ConstraintLayout>

マニフェスト

app\src\main\AndroidManifest.xml

    <uses-permission android:name="android.permission.CAMERA" />

を追記する。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.yamato200610a">

    <uses-permission android:name="android.permission.CAMERA" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

メイン処理


package com.example.yamato200610a

import android.Manifest
import android.app.Activity
import android.content.Intent
import android.content.pm.PackageManager
import android.graphics.Bitmap
import android.os.Bundle
import android.provider.MediaStore
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.core.app.ActivityCompat
import androidx.core.content.ContextCompat
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    companion object {
        const val CAMERA_REQUEST_CODE = 1
        const val CAMERA_PERMISSION_REQUEST_CODE = 2
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    override fun onResume() {
        super.onResume()
        btnLaunchCamera.setOnClickListener {
            Intent(MediaStore.ACTION_IMAGE_CAPTURE).resolveActivity(packageManager)?.let {
                if (checkCameraPermission()) {
                    takePicture()
                } else {
                    grantCameraPermission()
                }
            } ?: Toast.makeText(this, "camera app error", Toast.LENGTH_LONG).show()
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        if (requestCode == CAMERA_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
            val image = data?.extras?.get("data")?.let {
                cameraImage.setImageBitmap(it as Bitmap)
            }
        }
    }

    private fun takePicture() {
        val intent = Intent(MediaStore.ACTION_IMAGE_CAPTURE).apply {
            addCategory(Intent.CATEGORY_DEFAULT)
        }
        startActivityForResult(intent, CAMERA_REQUEST_CODE)
    }

    private fun checkCameraPermission() = PackageManager.PERMISSION_GRANTED ==
            ContextCompat.checkSelfPermission(applicationContext, Manifest.permission.CAMERA)

    private fun grantCameraPermission() =
            ActivityCompat.requestPermissions(this,
                    arrayOf(Manifest.permission.CAMERA),
                    CAMERA_PERMISSION_REQUEST_CODE)

    override fun onRequestPermissionsResult(requestCode: Int,
                                            permissions: Array<out String>,
                                            grantResults: IntArray) {
        if (requestCode == CAMERA_PERMISSION_REQUEST_CODE) {
            if (grantResults.isNotEmpty() &&
                    grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                takePicture()
            }
        }
    }
}

解説

カメラ起動ボタン

    override fun onResume() {
        super.onResume()
        btnLaunchCamera.setOnClickListener {
            Intent(MediaStore.ACTION_IMAGE_CAPTURE).resolveActivity(packageManager)?.let {
                if (checkCameraPermission()) {
                    takePicture()
                } else {
                    grantCameraPermission()
                }
            } ?: Toast.makeText(this, "camera app error", Toast.LENGTH_LONG).show()
        }
    }

カメラへのアクセス許可

    private fun checkCameraPermission() = PackageManager.PERMISSION_GRANTED ==
            ContextCompat.checkSelfPermission(applicationContext, Manifest.permission.CAMERA)

    private fun grantCameraPermission() =
            ActivityCompat.requestPermissions(this,
                    arrayOf(Manifest.permission.CAMERA),
                    CAMERA_PERMISSION_REQUEST_CODE)

    override fun onRequestPermissionsResult(requestCode: Int,
                                            permissions: Array<out String>,
                                            grantResults: IntArray) {
        if (requestCode == CAMERA_PERMISSION_REQUEST_CODE) {
            if (grantResults.isNotEmpty() &&
                    grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                takePicture()
            }
        }
    }

撮影した写真をビューに表示

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        if (requestCode == CAMERA_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
            val image = data?.extras?.get("data")?.let {
                cameraImage.setImageBitmap(it as Bitmap)
            }
        }
    }