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Android Camera2 で画像を表示るまでのおそらくこれが最低限のソースコード

package com.hanull.petscamera;

import android.Manifest;
import android.content.pm.PackageManager;
import android.graphics.ImageFormat;
import android.graphics.SurfaceTexture;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CaptureRequest;
import android.media.ImageReader;
import android.support.annotation.IntDef;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Surface;
import android.view.TextureView;

import java.lang.reflect.Array;
import java.util.Arrays;

public class MainActivity extends AppCompatActivity {
    private CameraDevice mCameraDevice;
    private CameraCaptureSession mCameraSession;
    private TextureView mTextureView;
    private CaptureRequest.Builder mPreviewBuilder;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        mTextureView = (TextureView) findViewById(R.id.camera2_texture);
        if(mTextureView.isAvailable()) {
            openCamera();

        } else {
            mTextureView.setSurfaceTextureListener(surfaceTextureListener);
        }
    }

    private void openCamera() {
        CameraManager cameraManager = (CameraManager) getSystemService(CAMERA_SERVICE);
        try {
            String selectedCameraId = cameraManager.getCameraIdList()[0];
            if(checkSelfPermission(Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {
                cameraManager.openCamera(selectedCameraId, stateCallback, null);
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull CameraDevice cameraDevice) {
            mCameraDevice = cameraDevice;
            SurfaceTexture texture = mTextureView.getSurfaceTexture();
            texture.setDefaultBufferSize(mTextureView.getWidth(), mTextureView.getHeight());
            Surface mPreViewSurface = new Surface(texture);
            try {
                cameraDevice.createCaptureSession(Arrays.asList(mPreViewSurface/*, mImageReader.getSurface()*/), sessionCallback, null);
                mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
                mPreviewBuilder.addTarget(mPreViewSurface);
                mPreviewBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }

        }

        @Override
        public void onDisconnected(@NonNull CameraDevice cameraDevice) {
            cameraDevice.close();
            mCameraDevice = null;
        }

        @Override
        public void onError(@NonNull CameraDevice cameraDevice, int error) {
            cameraDevice.close();
            mCameraDevice = null;
        }
    };

    CameraCaptureSession.StateCallback sessionCallback = new CameraCaptureSession.StateCallback() {
        @Override
        public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
            mCameraSession = cameraCaptureSession;
            try {
                mCameraSession.setRepeatingRequest(mPreviewBuilder.build(), null, null);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {

        }
    };

    TextureView.SurfaceTextureListener surfaceTextureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int i, int i1) {
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int i, int i1) {

        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
            return false;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {

        }
    };
}