Capture picture without preview using camera2 API
What I want to achieve is capturing a picture without showing the preview, sending directly the output to an ImageReader.
I have used the Camera2Basic example as a starting point.
However, the callback of my ImageReader is never called, hence no image is sent to its Surface.
Do I really need to display a preview first?
This is the camera code, which is ordered following the flow of the asynchronous callbacks:
private ImageReader imageReader;
private Handler backgroundHandler;
private HandlerThread backgroundThread;
private String cameraId;
private CameraDevice cameraDevice;
private CameraCaptureSession cameraCaptureSession;
@Override
public void onCreate() {
setupCamera2();
}
private void setupCamera2() {
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
try {
for (String cameraId : manager.getCameraIdList()) {
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
if (characteristics.get(CameraCharacteristics.LENS_FACING) != CameraCharacteristics.LENS_FACING_FRONT) {
continue;
}
this.cameraId = cameraId;
int[] picSize = Settings.getPictureSize();
int picWidth = picSize[0];
int picHeight = picSize[1];
imageReader = ImageReader.newInstance(picWidth, picHeight, ImageFormat.JPEG, 2);
imageReader.setOnImageAvailableListener(onImageAvailableListener, backgroundHandler);
}
} catch (CameraAccessException | NullPointerException e) {
e.printStackTrace();
}
}
private void openCamera2() {
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
try {
manager.openCamera(cameraId, cameraStateCallback, backgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private final CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(CameraDevice device) {
cameraDevice = device;
createCameraCaptureSession();
}
@Override
public void onDisconnected(CameraDevice cameraDevice) {}
@Override
public void onError(CameraDevice cameraDevice, int error) {}
};
private void createCaptureSession() {
List<Surface> outputSurfaces = new LinkedList<>();
outputSurfaces.add(imageReader.getSurface());
try {
cameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(CameraCaptureSession session) {
cameraCaptureSession = session;
}
@Override
public void onConfigureFailed(CameraCaptureSession session) {}
}, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private final ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
@Override
public void onImageAvailable(ImageReader reader) {
createCaptureRequest();
}
};
private void createCaptureRequest() {
try {
CaptureRequest.Builder requestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
requestBuilder.addTarget(imageReader.getSurface());
// Focus
requestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
// Orientation
int rotation = windowManager.getDefaultDisplay().getRotation();
requestBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
cameraCaptureSession.capture(requestBuilder.build(), camera2Callback, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
You should capture photos in "onConfigured" function but not onImageAvailable.
public void onConfigured(CameraCaptureSession session) {
cameraCaptureSession = session;
createCaptureRequest();
}
In this function "onImageAvailable",you should save images,
Image image = mImageReader.acquireLatestImage();
ByteBuffer buffer = image.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.remaining()];
buffer.get(bytes);
try {
save(bytes, file);
} catch (IOException e) {
e.printStackTrace();
}
image.close();
"onImageAvailable" function will be invoked after session.capture() .
Since I struggled a lot finding out how this works, here is a minimal working Android Service which can process Image data. It probably needs some time after create before you can call start the service, though!
import android.app.Service;
import android.content.Intent;
import android.graphics.ImageFormat;
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.Image;
import android.media.ImageReader;
import android.os.IBinder;
import android.util.Log;
import java.util.Arrays;
public class VideoProcessingService extends Service {
private static final String TAG = "VideoProcessing";
private static final int CAMERA = CameraCharacteristics.LENS_FACING_FRONT;
private CameraDevice camera;
private CameraCaptureSession session;
private ImageReader imageReader;
private CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(CameraDevice camera) {
VideoProcessingService.this.camera = camera;
}
@Override
public void onDisconnected(CameraDevice camera) {}
@Override
public void onError(CameraDevice camera, int error) {}
};
private CameraCaptureSession.StateCallback sessionStateCallback = new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(CameraCaptureSession session) {
VideoProcessingService.this.session = session;
try {
session.setRepeatingRequest(createCaptureRequest(), null, null);
} catch (CameraAccessException e){
Log.e(TAG, e.getMessage());
}
}
@Override
public void onConfigureFailed(CameraCaptureSession session) {}
};
private ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
@Override
public void onImageAvailable(ImageReader reader){
Image img = reader.acquireLatestImage();
processImage(img);
img.close();
}
};
@Override
public void onCreate() {
CameraManager manager = (CameraManager) getSystemService(CAMERA_SERVICE);
try {
manager.openCamera(getCamera(manager), cameraStateCallback, null);
imageReader = ImageReader.newInstance(320, 240, ImageFormat.YUV_420_888, 30 * 600); //fps * 10 min
imageReader.setOnImageAvailableListener(onImageAvailableListener, null);
} catch (CameraAccessException e){
Log.e(TAG, e.getMessage());
}
}
/**
* Return the Camera Id which matches the field CAMERA.
*/
public String getCamera(CameraManager manager){
try {
for (String cameraId : manager.getCameraIdList()) {
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
int cOrientation = characteristics.get(CameraCharacteristics.LENS_FACING);
if (cOrientation == CAMERA) {
return cameraId;
}
}
} catch (CameraAccessException e){
e.printStackTrace();
}
return null;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
try {
camera.createCaptureSession(Arrays.asList(imageReader.getSurface()), sessionStateCallback, null);
} catch (CameraAccessException e){
Log.e(TAG, e.getMessage());
}
return super.onStartCommand(intent, flags, startId);
}
@Override
public void onDestroy() {
try {
session.abortCaptures();
} catch (CameraAccessException e){
Log.e(TAG, e.getMessage());
}
session.close();
}
/**
* Process image data as desired.
*/
private void processImage(Image image){
//Process image data
}
private CaptureRequest createCaptureRequest() {
try {
CaptureRequest.Builder builder = camera.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);
builder.addTarget(imageReader.getSurface());
return builder.build();
} catch (CameraAccessException e) {
Log.e(TAG, e.getMessage());
return null;
}
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
}
I've been struggling with CAMERA2 API for a long time, looking for how to take pictures without preview from all available cameras on the device.
I ended up creating a project on GitHub that does exactly what you want (and maybe more)! https://github.com/hzitoun/android-camera2-secret-picture-taker
Hope that helped :)
Hey I had an issue with having a basic preview of the camera in a textureView. I found the best working solution to take a picture, save the picture to external directory and NOT break the preview! Camera2 API was buggy af. Enjoy <3. Also asks for permissions ahead!
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="theandroidguy.bart.keepreceipt">
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<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/Theme.AppCompat.Light.NoActionBar">
<activity android:name=".Insert_Receipt_Info_Activity"></activity>
<activity android:name=".ScanReceipt" />
<activity
android:name=".NavigationActivity"
android:label="KeepReceipt"
android:theme="@style/Theme.AppCompat.Light.NoActionBar" />
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".MainActivity" />
</application>
</manifest>
ScanReceipt.java
package theandroidguy.bart.keepreceipt;
import android.Manifest;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
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.CameraMetadata;
import android.hardware.camera2.CaptureRequest;
import android.hardware.camera2.TotalCaptureResult;
import android.hardware.camera2.params.StreamConfigurationMap;
import android.media.Image;
import android.media.ImageReader;
import android.os.Environment;
import android.os.Handler;
import android.os.HandlerThread;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.util.Size;
import android.util.SparseIntArray;
import android.view.Surface;
import android.view.TextureView;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;
public class ScanReceipt extends AppCompatActivity{
private Button btnCapture;
private TextureView textureView;
public static final int STORAGE_PERMISSION_REQUEST_CODE= 1;
//Check state orientation of output image
private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
static{
ORIENTATIONS.append(Surface.ROTATION_0,90);
ORIENTATIONS.append(Surface.ROTATION_90,0);
ORIENTATIONS.append(Surface.ROTATION_180,270);
ORIENTATIONS.append(Surface.ROTATION_270,180);
}
private String cameraId;
private CameraDevice cameraDevice;
private CameraCaptureSession cameraCaptureSessions;
private CaptureRequest.Builder captureRequestBuilder;
private Size imageDimension;
private ImageReader imageReader;
//Save to FILE
private File file;
private static final int REQUEST_CAMERA_PERMISSION = 200;
private boolean mFlashSupported;
private Handler mBackgroundHandler;
private HandlerThread mBackgroundThread;
CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(@NonNull CameraDevice camera) {
cameraDevice = camera;
createCameraPreview();
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
cameraDevice.close();
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int i) {
cameraDevice.close();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_scan_receipt);
askPermissions();
textureView = findViewById(R.id.textureView);
//From Java 1.4 , you can use keyword 'assert' to check expression true or false
assert textureView != null;
textureView.setSurfaceTextureListener(textureListener);
btnCapture = findViewById(R.id.snapPictureBtn);
btnCapture.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
takePicture();
}
});
}
protected void takePicture() {
if(null == cameraDevice) {
Log.e("No cam", "cameraDevice is null and not being detected!!!");
return;
}
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
try {
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraDevice.getId());
Size[] jpegSizes = null;
if (characteristics != null) {
jpegSizes = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP).getOutputSizes(ImageFormat.JPEG);
}
int width = 640;
int height = 480;
if (jpegSizes != null &&
0 < jpegSizes.length) {
width = jpegSizes[0].getWidth();
height = jpegSizes[0].getHeight();
}
final ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
List<Surface> outputSurfaces = new ArrayList<Surface>(2);
outputSurfaces.add(reader.getSurface());
//i believe this fucks over the preview after snapping
//outputSurfaces.add(new Surface(textureView.getSurfaceTexture()));
final CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.addTarget(reader.getSurface());
captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
// Orientation
int rotation = getWindowManager().getDefaultDisplay().getRotation();
captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
final File file = new File(Environment.getExternalStorageDirectory()+"/picture.jpg");
ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
@Override
public void onImageAvailable(ImageReader reader) {
Image image = null;
try {
image = reader.acquireLatestImage();
ByteBuffer buffer = image.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.capacity()];
buffer.get(bytes);
save(bytes);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (image != null) {
image.close();
}
}
}
private void save(byte[] bytes) throws IOException {
OutputStream output = null;
try {
output = new FileOutputStream(file);
output.write(bytes);
} finally {
if (null != output) {
output.close();
}
}
}
};
reader.setOnImageAvailableListener(readerListener, mBackgroundHandler);
final CameraCaptureSession.CaptureCallback captureListener = new CameraCaptureSession.CaptureCallback() {
@Override
public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
super.onCaptureCompleted(session, request, result);
Toast.makeText(ScanReceipt.this, "Saved:" + file, Toast.LENGTH_SHORT).show();
createCameraPreview();
}
};
cameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession session) {
try {
session.capture(captureBuilder.build(), captureListener, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession session) {
Toast.makeText(getApplicationContext(), "Failed on config!", Toast.LENGTH_SHORT).show();
}
}, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void createCameraPreview() {
try{
SurfaceTexture texture = textureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(imageDimension.getWidth(),imageDimension.getHeight());
Surface surface = new Surface(texture);
captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
captureRequestBuilder.addTarget(surface);
cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
if(cameraDevice == null)
return;
cameraCaptureSessions = cameraCaptureSession;
updatePreview();
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
Toast.makeText(ScanReceipt.this, "Changed", Toast.LENGTH_SHORT).show();
}
},null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void updatePreview() {
if(cameraDevice == null)
Toast.makeText(this, "Error", Toast.LENGTH_SHORT).show();
captureRequestBuilder.set(CaptureRequest.CONTROL_MODE,CaptureRequest.CONTROL_MODE_AUTO);
try{
cameraCaptureSessions.setRepeatingRequest(captureRequestBuilder.build(),null,mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void openCamera() {
CameraManager manager = (CameraManager)getSystemService(Context.CAMERA_SERVICE);
try{
cameraId = manager.getCameraIdList()[0];
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
assert map != null;
imageDimension = map.getOutputSizes(SurfaceTexture.class)[0];
//Check realtime permission if run higher API 23
if(ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)
{
ActivityCompat.requestPermissions(this,new String[]{
Manifest.permission.CAMERA,
Manifest.permission.WRITE_EXTERNAL_STORAGE
},REQUEST_CAMERA_PERMISSION);
return;
}
manager.openCamera(cameraId,stateCallback,null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
TextureView.SurfaceTextureListener textureListener = 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 true;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
}
};
@Override
protected void onResume() {
super.onResume();
startBackgroundThread();
if(textureView.isAvailable())
openCamera();
else
textureView.setSurfaceTextureListener(textureListener);
}
@Override
protected void onPause() {
stopBackgroundThread();
super.onPause();
}
private void stopBackgroundThread() {
mBackgroundThread.quitSafely();
try{
mBackgroundThread.join();
mBackgroundThread= null;
mBackgroundHandler = null;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private void startBackgroundThread() {
mBackgroundThread = new HandlerThread("Camera Background");
mBackgroundThread.start();
mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}
private void askPermissions() {
int permissionCheckStorage = ContextCompat.checkSelfPermission(this,
Manifest.permission.WRITE_EXTERNAL_STORAGE);
// we already asked for permisson & Permission granted, call camera intent
if (permissionCheckStorage == PackageManager.PERMISSION_GRANTED) {
//do what you want
} else {
// if storage request is denied
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("You need to give permission to access storage in order to work this feature.");
builder.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
dialogInterface.dismiss();
finish();
}
});
builder.setPositiveButton("GIVE PERMISSION", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
dialogInterface.dismiss();
// Show permission request popup
ActivityCompat.requestPermissions(ScanReceipt.this,
new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
STORAGE_PERMISSION_REQUEST_CODE);
}
});
builder.show();
} //asking permission for first time
else {
// Show permission request popup for the first time
ActivityCompat.requestPermissions(ScanReceipt.this,
new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
STORAGE_PERMISSION_REQUEST_CODE);
}
}
}
}
Activity_Scan_Receipt.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/Relvativelayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ScanReceipt">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="8dp"
android:gravity="center"
android:text="Add new receipt"
android:textAlignment="center"
android:textSize="16sp"
app:layout_constraintBottom_toTopOf="@+id/snapPictureBtn"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/receiptscan" />
<TextView
android:id="@+id/progressStatusText"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:layout_below="@+id/receiptscan"
android:layout_marginTop="8dp"
android:padding="16dp"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:text="Scan Receipt"
android:textAlignment="center"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/snapPictureBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/progressStatusText"
android:layout_marginStart="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="16dp"
android:text="Snap"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent" />
<android.support.v7.widget.CardView
android:id="@+id/receiptscan"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_below="@+id/textView"
android:layout_marginStart="24dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="24dp"
android:layout_marginBottom="8dp"
android:padding="16dp"
app:cardCornerRadius="18dp"
app:layout_constraintBottom_toTopOf="@+id/textView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/progressStatusText">
<TextureView
android:id="@+id/textureView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView"
android:gravity="center"
app:layout_constraintTop_toBottomOf="@+id/textView" />
</android.support.v7.widget.CardView>
</android.support.constraint.ConstraintLayout>