我制作自定义相机Android应用程序。我已经添加了一个按钮，可以在我的活动中切换相机。单击该按钮，我的相机完全切换，但当我尝试通过回调保存图像时，我的应用程序由于NullPointerException而崩溃。这是我的代码。请帮我。 提前谢谢
相机活动代码
public class CameraActivity extends Activity {
private Camera mCamera;
private CameraHandler surface_view;
public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;
public static final String TAG="Aloo";
Bitmap bmp;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.camera);
if(checkifCamera(this))
{
mCamera=getCameraInstance();
surface_view = new CameraHandler(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(surface_view);
}
else
{
Toast.makeText(this,"Sorry camera is not supported on your device",Toast.LENGTH_LONG).show();
}
}
private boolean checkifCamera(Context context)
{
if(context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA))
{
return true;
}
else {
return false;
}
}
public Camera getCameraInstance()
{
Toast.makeText(this,"Chrj",Toast.LENGTH_LONG).show();
Camera c=null;
try{
releaseCameraAndPreview();
c=Camera.open();
}
catch (Exception e)
{
Toast.makeText(this,"Print error"+e.getMessage(),Toast.LENGTH_LONG).show();
return c;
}
Toast.makeText(this,"Check this out "+c,Toast.LENGTH_LONG).show();
return c;
}
public void switchC(View view)//Function called to switch camera
{
surface_view.switchCamera();
mCamera=getCameraInstance();
}
private void releaseCameraAndPreview() {
if (mCamera != null) {
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}
@Override
protected void onPause() {
super.onPause();
try
{
// release the camera immediately on pause event
//releaseCamera();
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
mCamera.release();
mCamera = null;
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void takePH(View view)
{
int toRotate=0;
Display display = ((WindowManager)getSystemService(WINDOW_SERVICE)).getDefaultDisplay();
int displayRotation = display.getRotation();
switch (displayRotation) {
case Surface.ROTATION_0: toRotate=90; break;
case Surface.ROTATION_90: break;
case Surface.ROTATION_180: break;
case Surface.ROTATION_270: toRotate=270; break;
}
Toast.makeText(this,"Rotation "+toRotate,Toast.LENGTH_LONG).show();
Camera.Parameters params = mCamera.getParameters();
params.set("rotation",270);
mCamera.setParameters(params);
mCamera.takePicture(null,null,mPicture);
}
Camera.PictureCallback mPicture = new Camera.PictureCallback() {
@Override
public void onPictureTaken(byte[] data, Camera camera) {
File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
if (pictureFile == null){
Log.d(TAG, "Error creating media file, check storage permissions: ");
return;
}
try {
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(data);
fos.close();
} catch (FileNotFoundException e) {
Log.d(TAG, "File not found: " + e.getMessage());
} catch (IOException e) {
Log.d(TAG, "Error accessing file: " + e.getMessage());
}
Toast.makeText(CameraActivity.this,"Image saves successfully", Toast.LENGTH_LONG).show();
}
};
/** Create a file Uri for saving an image or video */
private static Uri getOutputMediaFileUri(int type){
return Uri.fromFile(getOutputMediaFile(type));
}
/** Create a File for saving an image or video */
private static File getOutputMediaFile(int type){
// To be safe, you should check that the SDCard is mounted
// using Environment.getExternalStorageState() before doing this.
File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES), "Fotos");
// This location works best if you want the created images to be shared
// between applications and persist after your app has been uninstalled.
// Create the storage directory if it does not exist
if (! mediaStorageDir.exists()){
if (! mediaStorageDir.mkdirs()){
Log.d("MyCameraApp", "failed to create directory");
return null;
}
}
// Create a media file name
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
File mediaFile;
if (type == MEDIA_TYPE_IMAGE){
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"IMG_"+ timeStamp + ".jpg");
} else if(type == MEDIA_TYPE_VIDEO) {
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"VID_"+ timeStamp + ".mp4");
} else {
return null;
}
return mediaFile;
}
}
我的自定义相机处理程序
public class CameraHandler extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera=null;
public int currentCameraID=0;
public CameraHandler(Context context,Camera camera) {
super(context);
mCamera=camera;
mHolder=getHolder();
mHolder.addCallback(this);
mHolder.setType(SurfaceHolder.SURFACE_TYPE_GPU);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
try {
mCamera.setPreviewDisplay(holder);
Camera.Parameters p = mCamera.getParameters();
}
catch (IOException e)
{
Log.d("--DS", "Error setting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
fixOr();
if(mHolder.getSurface()==null)
{
return;
}
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 {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e){
Log.d("--DS", "Error starting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
mCamera.setPreviewCallback(null);
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
public void fixOr()
{
mCamera.stopPreview();
mCamera.setDisplayOrientation(90);
mCamera.startPreview();
}
public void switchCamera() {
mCamera.stopPreview();
mCamera.release();
if(currentCameraID==Camera.CameraInfo.CAMERA_FACING_BACK)
{
currentCameraID = Camera.CameraInfo.CAMERA_FACING_FRONT;
}
else
{
currentCameraID=Camera.CameraInfo.CAMERA_FACING_BACK;
}
mCamera=Camera.open(currentCameraID);
fixOr();
try {
mCamera.setPreviewDisplay(mHolder);
} catch (IOException e) {
e.printStackTrace();
}
mCamera.startPreview();
}
}
我相信我的应用程序崩溃了，因为当我切换相机时mCamera变为null。我该如何解决这个问题？
我得到的错误是：
java.lang.IllegalStateException: Could not execute method of the activity
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method
'android.hardware.Camera$Parameters android.hardware.Camera.getParameters()'
on a null object reference
答案 0 :(得分：0)
在听完拉米的评论后，我在2个地方改变了我的代码 1。）
public void switchC(View view)//Function called to switch camera
{
mCamera=surface_view.switchCamera();
}
2.）切换相机功能
public Camera switchCamera() {
mCamera.stopPreview();
mCamera.release();
if(currentCameraID==Camera.CameraInfo.CAMERA_FACING_BACK)
{
currentCameraID = Camera.CameraInfo.CAMERA_FACING_FRONT;
}
else
{
currentCameraID=Camera.CameraInfo.CAMERA_FACING_BACK;
}
mCamera=Camera.open(currentCameraID);
fixOr();
try {
mCamera.setPreviewDisplay(mHolder);
} catch (IOException e) {
e.printStackTrace();
}
mCamera.startPreview();
} return mCamera;