我正在尝试根据位于https://android.jlelse.eu/the-least-you-can-do-with-camera2-api-2971c8c81b8b
的教程来实现一个简单的相机照片捕获应用程序该应用首次运行良好。预览显示，我可以拍摄正确保存的照片。
我的问题是，当我关闭应用程序，回弹，最小化应用程序等...然后返回相机活动时，预览不再显示任何内容，并且当我尝试拍照时应用程序崩溃
我几乎肯定我没有以某种方式正确关闭相机，但是与有效的实现相比，我逐行梳理了代码，而我看不到自己在做什么不同/错误。
package com.example.cameratest;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.Point;
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.hardware.camera2.params.StreamConfigurationMap;
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.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Size;
import android.view.Display;
import android.view.Surface;
import android.view.TextureView;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Toast;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Collections;
import java.util.Date;
import java.util.Locale;
public class SecondCamera extends AppCompatActivity {
// Define the variables we need to use the camera
// Our request code can be anything. I like 8.
private static final int CAMERA_REQUEST_CODE = 8;
private CameraManager cameraManager;
private int cameraFacing;
private TextureView.SurfaceTextureListener surfaceTextureListener;
private String cameraId;
private Size previewSize;
private CameraDevice cameraDevice;
private TextureView textureView;
private CameraCaptureSession cameraCaptureSession;
private HandlerThread backgroundThread;
private Handler backgroundHandler;
private CameraDevice.StateCallback stateCallback;
private CaptureRequest.Builder captureRequestBuilder;
private CaptureRequest captureRequest;
private File galleryFolder;
private WindowManager windowManager;
private int windowHeight;
private int windowWidth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second_camera);
// Get the size of our display in order to properly scale the camera view
Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
windowHeight = size.y;
windowWidth = size.x;
textureView = (TextureView) findViewById(R.id.cameraTextureView);
// Let's ask for permission to use the camera feature
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE}, CAMERA_REQUEST_CODE);
// Get the camera system service
cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
// Make sure we use the back camera
cameraFacing = CameraCharacteristics.LENS_FACING_BACK;
// Set up a listener to communicate to our TextureView
surfaceTextureListener = new TextureView.SurfaceTextureListener(){
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
setUpCamera();
openCamera();
}
@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int width, int height) {
}
@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
return false;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
}
};
textureView.setSurfaceTextureListener(surfaceTextureListener);
// Manage the three states of our CameraDevice. Opened, Closed, and Error
stateCallback = new CameraDevice.StateCallback(){
@Override
public void onOpened(@NonNull CameraDevice cameraDevice) {
// Grab our camera device and start up the preview
SecondCamera.this.cameraDevice = cameraDevice;
createPreviewSession();
createImageGallery();
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
// Close and disconnect the cameraDevice
cameraDevice.close();
SecondCamera.this.cameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int i) {
// Close and disconnect the cameraDevice
cameraDevice.close();
SecondCamera.this.cameraDevice = null;
}
};
}
@Override
protected void onResume(){
super.onResume();
openBackgroundThread();
// If our texture view is available, let's set up and open the camera on it.
if(textureView.isAvailable()){
setUpCamera();
openCamera();
} else {
// If not, we need to set up the SurfaceTextureListener,
// which will do the same once the texture view is available
textureView.setSurfaceTextureListener(surfaceTextureListener);
}
}
@Override
protected void onPause(){
// Close the Camera and Background Thread to avoid memory leakage
closeBackgroundThread();
closeCamera();
super.onPause();
}
/**
* Close the CameraCaptureSession and CameraDevice
*/
private void closeCamera(){
if (cameraCaptureSession != null){
cameraCaptureSession.close();
cameraCaptureSession = null;
}
if (cameraDevice != null){
cameraDevice.close();
cameraDevice = null;
}
}
/**
* Shut down our backgroundThread and handler
*/
private void closeBackgroundThread(){
backgroundThread.quitSafely();
try {
backgroundThread.join();
backgroundThread = null;
backgroundHandler = null;
} catch (InterruptedException ie){
ie.printStackTrace();
}
}
/**
* Open a thread in the background in order to run the camera
*/
private void openBackgroundThread(){
backgroundThread = new HandlerThread("Camera Background Thread");
backgroundThread.start();
backgroundHandler = new Handler(backgroundThread.getLooper());
}
/**
* Establish the camera to use, and get information to scale our preview correctly
*/
private void setUpCamera(){
try{
for (String cameraID: cameraManager.getCameraIdList()){
CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraID);
// If we find the appropriate camera:
if (characteristics.get(CameraCharacteristics.LENS_FACING) == cameraFacing){
// Get the preview size we need, and set this class's camera ID
StreamConfigurationMap streamConfigurationMap = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
// The first element in the list of output sizes is the highest resolution one.
// Get a Size object which is prepared for a SurfaceTexture.
Size[] possibleSizes = streamConfigurationMap.getOutputSizes(SurfaceTexture.class);
previewSize = chooseOptimalSize(possibleSizes, windowWidth, windowHeight);
this.cameraId = cameraID;
}
}
if (this.cameraId == null){
Toast.makeText(this, "ERROR, NO CAMERA FOUND", Toast.LENGTH_SHORT).show();
}
} catch (CameraAccessException cae){
cae.printStackTrace();
}
}
/**
* Attempt to open the camera in the background thread
* if we find that we have been granted permission.
*/
private void openCamera(){
try {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED){
cameraManager.openCamera(cameraId, stateCallback, backgroundHandler);
}
else {
Toast.makeText(this, "Camera Permissions must be enabled for this activity to function", Toast.LENGTH_SHORT).show();
}
} catch (CameraAccessException cae){
cae.printStackTrace();
}
}
/**
* Initialize a preview for our camera screen, so the user can
* see in real time what the camera sees.
*/
private void createPreviewSession(){
try {
// Get the surfaceTexture out of our textureView. This is what we stream to
SurfaceTexture surfaceTexture = textureView.getSurfaceTexture();
// We want to set our size correctly based on the preview Size from before
surfaceTexture.setDefaultBufferSize(previewSize.getWidth(), previewSize.getHeight());
// Set up a Surface based on our Surface Texture
Surface previewSurface = new Surface(surfaceTexture);
// We want to build a request for a preview style stream, and send it to our surface
captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
captureRequestBuilder.addTarget(previewSurface);
cameraDevice.createCaptureSession(Collections.singletonList(previewSurface), new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
if (cameraDevice != null){
try {
captureRequest = captureRequestBuilder.build();
SecondCamera.this.cameraCaptureSession = cameraCaptureSession;
SecondCamera.this.cameraCaptureSession.setRepeatingRequest(captureRequest, null, backgroundHandler);
} catch (CameraAccessException cae) {
cae.printStackTrace();
}
}
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
// Do nothing?
}
}, backgroundHandler);
} catch (CameraAccessException cae){
cae.printStackTrace();
}
}
/**
* Initialize a folder in our pictures library to save photos to
*/
private void createImageGallery(){
File storageDirectory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
galleryFolder = new File(storageDirectory, getResources().getString(R.string.app_name));
if (!galleryFolder.exists()){
boolean wasCreated = galleryFolder.mkdirs();
if (!wasCreated){
System.out.println("Failed to create directory " + galleryFolder.getPath());
}
}
}
/**
* Create a temp file to store our image to
*/
private File createImageFile(File galleryFolder) throws IOException {
// Grab our timestamp and use it to create a unique image name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmsss", Locale.getDefault()).format(new Date());
String imageFilename = getResources().getString(R.string.app_name) + timeStamp;
Toast.makeText(this, "Created image " + imageFilename + ".jpg", Toast.LENGTH_SHORT).show();
return File.createTempFile(imageFilename, ".jpg", galleryFolder);
}
/**
* Capture everything on the screen, and output it to our file
*/
public void takePhoto(View view){
try (FileOutputStream outputPhoto = new FileOutputStream(createImageFile(galleryFolder))) {
lock();
textureView.getBitmap().compress(Bitmap.CompressFormat.PNG, 100, outputPhoto);
} catch (IOException ioe) {
ioe.printStackTrace();
} finally {
unlock();
}
}
/**
* Lock our camera preview, as if the shutter of a camera
*/
private void lock(){
try {
// Lock the screen for a second
cameraCaptureSession.capture(captureRequestBuilder.build(), null, backgroundHandler);
} catch (CameraAccessException cae){
cae.printStackTrace();
}
}
/**
* Unlock our camera preview, allowing the user to see freely again
*/
private void unlock(){
try {
// Go back to the repeating preview request
cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(),
null, backgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
/**
* Do some calculations to figure out how to show the correct
* aspect ratio for our camera preview
*
* @param outputSizes The array of possible output sizes
* @param width The width of our device screen
* @param height The height of our device screen
* @return The size to set our display to
*/
private Size chooseOptimalSize(Size[] outputSizes, int width, int height) {
double preferredRatio = height / (double) width;
Size currentOptimalSize = outputSizes[0];
double currentOptimalRatio = currentOptimalSize.getWidth() / (double) currentOptimalSize.getHeight();
for (Size currentSize : outputSizes) {
double currentRatio = currentSize.getWidth() / (double) currentSize.getHeight();
if (Math.abs(preferredRatio - currentRatio) <
Math.abs(preferredRatio - currentOptimalRatio)) {
currentOptimalSize = currentSize;
currentOptimalRatio = currentRatio;
}
}
return currentOptimalSize;
}
}
在崩溃的日志中，我看到：
E/CameraDeviceState: Cannot call configure while in state: 0
E/AndroidRuntime: FATAL EXCEPTION: Camera Background Thread
Process: com.example.cameratest, PID: 21313
java.lang.IllegalStateException: Session has been closed; further changes are illegal.
at android.hardware.camera2.impl.CameraCaptureSessionImpl.checkNotClosed(CameraCaptureSessionImpl.java:627)
at android.hardware.camera2.impl.CameraCaptureSessionImpl.setRepeatingRequest(CameraCaptureSessionImpl.java:234)
at com.example.cameratest.SecondCamera$3.onConfigured(SecondCamera.java:263)
at java.lang.reflect.Method.invoke(Native Method)
at android.hardware.camera2.dispatch.InvokeDispatcher.dispatch(InvokeDispatcher.java:39)
at android.hardware.camera2.dispatch.HandlerDispatcher$1.run(HandlerDispatcher.java:65)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.os.HandlerThread.run(HandlerThread.java:61)
这使我现在相信我的CameraCaputreSession出了点问题，但是我不知道是什么。
更改线路
cameraManager.openCamera(cameraId, stateCallback, backgroundHandler);
在我的openCamera（）方法中，将空值作为第三个参数而不是我的backgroundHandler似乎已对其进行了修复，但是说实话，我绝对不知道为什么。有人可以向我解释吗？这是正确的解决方案吗？
答案 0 :(得分：0)
一种可能性-您可以在onResume（）中启动后台线程，但也可以尝试在TextureViewListener的onSurfaceTextureAvailable中打开相机。
在第一次启动时，您仅在onResume中设置了后台线程之后才连接TextureViewListener，但是您绝不会注销该监听器。在第二次启动时，可能onSurfaceTextureAvailable回调在onResume（）之前运行，因为应用程序UI在onStart（）而不是onResume（）中可见。
这将使用空的后台线程打开摄像机（进入主线程），然后onResume将触发，并再次打开摄像机，从onSurfaceTextureAvailable中退出第一个摄像机对象。在第一个相机对象上进行进一步操作时会导致错误。
一种解决方法是，仅在onPaused中注销TextureViewListener或重组事物，以便尽早获取onSurfaceTextureAvailable回调也可以设置后台线程。