Android摄像头为空？ [英] Android Camera is null?
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问题描述
我已经花了一些时间调试，想不通为什么空正在发生。当我运行的应用程序immeditaley崩溃，并指出这行：
I have spent some time debugging and can't figure why null is occurring. When I run the application immeditaley it crashes and it points to this line:
mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
和表示，对象引用为空。我想不通为什么mCamera是返回null。
and says the object reference is null. I can't figure out why mCamera is returning null.
我的清单文件具有适当的权限：
My Manifest file has the proper permissions:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />
<uses-feature android:name="android.hardware.camera.front" android:required="false" />
例如：
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.hardware.Camera.PictureCallback;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Toast;
public class AndroidCameraExample extends Activity {
private Camera mCamera;
private CameraPreview mPreview;
private PictureCallback mPicture;
private Button capture, switchCamera;
private Context myContext;
private LinearLayout cameraPreview;
private boolean cameraFront = false;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
myContext = this;
initialize();
}
private int findFrontFacingCamera() {
int cameraId = -1;
// Search for the front facing camera
int numberOfCameras = Camera.getNumberOfCameras();
for (int i = 0; i < numberOfCameras; i++) {
CameraInfo info = new CameraInfo();
Camera.getCameraInfo(i, info);
if (info.facing == CameraInfo.CAMERA_FACING_FRONT) {
cameraId = i;
cameraFront = true;
break;
}
}
return cameraId;
}
private int findBackFacingCamera() {
int cameraId = -1;
//Search for the back facing camera
//get the number of cameras
int numberOfCameras = Camera.getNumberOfCameras();
//for every camera check
for (int i = 0; i < numberOfCameras; i++) {
CameraInfo info = new CameraInfo();
Camera.getCameraInfo(i, info);
if (info.facing == CameraInfo.CAMERA_FACING_BACK) {
cameraId = i;
cameraFront = false;
break;
}
}
return cameraId;
}
public void onResume() {
super.onResume();
if (!hasCamera(myContext)) {
Toast toast = Toast.makeText(myContext, "Sorry, your phone does not have a camera!", Toast.LENGTH_LONG);
toast.show();
finish();
}
if (mCamera == null) {
//if the front facing camera does not exist
if (findFrontFacingCamera() < 0) {
Toast.makeText(this, "No front facing camera found.", Toast.LENGTH_LONG).show();
switchCamera.setVisibility(View.GONE);
}
mCamera = Camera.open(findBackFacingCamera());
mPicture = getPictureCallback();
mPreview.refreshCamera(mCamera);
}
}
public void initialize() {
cameraPreview = (LinearLayout) findViewById(R.id.camera_preview);
mPreview = new CameraPreview(myContext, mCamera);
cameraPreview.addView(mPreview);
capture = (Button) findViewById(R.id.button_capture);
capture.setOnClickListener(captrureListener);
switchCamera = (Button) findViewById(R.id.button_ChangeCamera);
switchCamera.setOnClickListener(switchCameraListener);
}
OnClickListener switchCameraListener = new OnClickListener() {
@Override
public void onClick(View v) {
//get the number of cameras
int camerasNumber = Camera.getNumberOfCameras();
if (camerasNumber > 1) {
//release the old camera instance
//switch camera, from the front and the back and vice versa
releaseCamera();
chooseCamera();
} else {
Toast toast = Toast.makeText(myContext, "Sorry, your phone has only one camera!", Toast.LENGTH_LONG);
toast.show();
}
}
};
public void chooseCamera() {
//if the camera preview is the front
if (cameraFront) {
int cameraId = findBackFacingCamera();
if (cameraId >= 0) {
//open the backFacingCamera
//set a picture callback
//refresh the preview
mCamera = Camera.open(cameraId);
mPicture = getPictureCallback();
mPreview.refreshCamera(mCamera);
}
} else {
int cameraId = findFrontFacingCamera();
if (cameraId >= 0) {
//open the backFacingCamera
//set a picture callback
//refresh the preview
mCamera = Camera.open(cameraId);
mPicture = getPictureCallback();
mPreview.refreshCamera(mCamera);
}
}
}
@Override
protected void onPause() {
super.onPause();
//when on Pause, release camera in order to be used from other applications
releaseCamera();
}
private boolean hasCamera(Context context) {
//check if the device has camera
if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
return true;
} else {
return false;
}
}
private PictureCallback getPictureCallback() {
PictureCallback picture = new PictureCallback() {
@Override
public void onPictureTaken(byte[] data, Camera camera) {
//make a new picture file
File pictureFile = getOutputMediaFile();
if (pictureFile == null) {
return;
}
try {
//write the file
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(data);
fos.close();
Toast toast = Toast.makeText(myContext, "Picture saved: " + pictureFile.getName(), Toast.LENGTH_LONG);
toast.show();
} catch (FileNotFoundException e) {
} catch (IOException e) {
}
//refresh camera to continue preview
mPreview.refreshCamera(mCamera);
}
};
return picture;
}
OnClickListener captrureListener = new OnClickListener() {
@Override
public void onClick(View v) {
mCamera.takePicture(null, null, mPicture);
}
};
//make picture and save to a folder
private static File getOutputMediaFile() {
//make a new file directory inside the "sdcard" folder
File mediaStorageDir = new File("/sdcard/", "JCG Camera");
//if this "JCGCamera folder does not exist
if (!mediaStorageDir.exists()) {
//if you cannot make this folder return
if (!mediaStorageDir.mkdirs()) {
return null;
}
}
//take the current timeStamp
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
File mediaFile;
//and make a media file:
mediaFile = new File(mediaStorageDir.getPath() + File.separator + "IMG_" + timeStamp + ".jpg");
return mediaFile;
}
private void releaseCamera() {
// stop and release camera
if (mCamera != null) {
mCamera.release();
mCamera = null;
}
}
}
相机preVIEW：
CameraPreview:
import java.io.IOException;
import java.util.List;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private static final String TAG = "CameraPreview";
private Context mContext;
private SurfaceHolder mHolder;
private Camera mCamera;
private List<Camera.Size> mSupportedPreviewSizes;
private Camera.Size mPreviewSize;
public CameraPreview(Context context, Camera camera) {
super(context);
mContext = context;
mCamera = camera;
// supported preview sizes
mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
for (Camera.Size str : mSupportedPreviewSizes)
Log.e(TAG, str.width + "/" + str.height);
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void surfaceCreated(SurfaceHolder holder) {
// empty. surfaceChanged will take care of stuff
}
public void surfaceDestroyed(SurfaceHolder holder) {
// empty. Take care of releasing the Camera preview in your activity.
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
Log.e(TAG, "surfaceChanged => w=" + w + ", h=" + h);
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e){
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or reformatting changes here
// start preview with new settings
try {
Camera.Parameters parameters = mCamera.getParameters();
parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
mCamera.setParameters(parameters);
mCamera.setDisplayOrientation(90);
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
if (mSupportedPreviewSizes != null) {
mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width, height);
}
float ratio;
if(mPreviewSize.height >= mPreviewSize.width)
ratio = (float) mPreviewSize.height / (float) mPreviewSize.width;
else
ratio = (float) mPreviewSize.width / (float) mPreviewSize.height;
// One of these methods should be used, second method squishes preview slightly
setMeasuredDimension(width, (int) (width * ratio));
// setMeasuredDimension((int) (width * ratio), height);
}
private Camera.Size getOptimalPreviewSize(List<Camera.Size> sizes, int w, int h) {
final double ASPECT_TOLERANCE = 0.1;
double targetRatio = (double) h / w;
if (sizes == null)
return null;
Camera.Size optimalSize = null;
double minDiff = Double.MAX_VALUE;
int targetHeight = h;
for (Camera.Size size : sizes) {
double ratio = (double) size.height / size.width;
if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE)
continue;
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
if (optimalSize == null) {
minDiff = Double.MAX_VALUE;
for (Camera.Size size : sizes) {
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
}
return optimalSize;
}
public void refreshCamera(Camera camera) {
if (mHolder.getSurface() == null) {
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e) {
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
setCamera(camera);
try {
Camera.Parameters parameters = mCamera.getParameters();
parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
mCamera.setParameters(parameters);
mCamera.setDisplayOrientation(90);
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e) {
Log.d(VIEW_LOG_TAG, "Error starting camera preview: " + e.getMessage());
}
}
public void setCamera(Camera camera) {
//method to set a camera instance
mCamera = camera;
}
}
由于我使用的教程，如果我用这台相机preview.java代替（保持同样的例子类）它的工作原理，但我需要做一些修改教程宽高比原因：
As I am using a tutorial, if I use this CameraPreview.java instead (keeping the same Example class) it works, but I needed to make some modifications to the tutorial for the aspect ratio reasons:
import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void surfaceCreated(SurfaceHolder holder) {
try {
// create the surface and start camera preview
if (mCamera == null) {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
}
} catch (IOException e) {
Log.d(VIEW_LOG_TAG, "Error setting camera preview: " + e.getMessage());
}
}
public void refreshCamera(Camera camera) {
if (mHolder.getSurface() == null) {
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e) {
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
setCamera(camera);
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e) {
Log.d(VIEW_LOG_TAG, "Error starting camera preview: " + e.getMessage());
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
refreshCamera(mCamera);
}
public void setCamera(Camera camera) {
//method to set a camera instance
mCamera = camera;
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
// mCamera.release();
}
}
更新：此外，我试图把 chooseCamera（）; 前右侧的米preVIEW =新相机preVIEW（myContext ，mCamera）; ，但没有奏效。
UPDATE: Additionally I tried to put chooseCamera(); right before the mPreview = new CameraPreview(myContext, mCamera); but it did not work.
推荐答案
我有一个猜想，因为我没有测试code，但它看为是，我认为你是在调用初始化（ ），再进行实例的实际Camera对象。观察这张照片了Android生命周期的：
I have a guess, as I haven't tested this code, but from looking at it as is, I think that you are calling initialize() before you are instantiating your actually Camera object. Observe this picture of the Android life cycle:
您会发现，onResume（）被调用的 后的onCreate（）。在您的code，你通过调用初始化（）方法创建的onCreate用在你的空mCamera参考相机preVIEW类（）。因此，在摄像头preVIEW行：
You will notice that onResume() is called AFTER onCreate(). In your code you are creating the CameraPreview class with your null mCamera reference in the by calling the initialize() method in onCreate(). Therefore, the line in CameraPreview:
mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
在呼唤一个空对象引用，mCamera。相反，移动
is calling a null object reference, mCamera. Instead, move
mCamera = Camera.open(findBackFacingCamera());
要的onCreate（）的（之前调用初始化过程中的相机preVIEW！）的，保持在onResume相同的呼叫（）。保持支票在onResume（）的情况下在用户离开的活性和摄像机被关闭因某种原因空相机
to onCreate() (before the call to initialize CameraPreview of course!), keeping the same call in onResume(). Keep the check for a null Camera in onResume() in case the user leaves the activity and Camera is closed for some reason.
这篇关于Android摄像头为空？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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