我无法访问我的activity.getpicture方法中的错误，我该如何解决它。
CamTestActivity
public class CamTestActivity extends Activity {
private static final String TAG = "CamTestActivity";
Preview preview;
Button buttonClick;
Camera camera;
Activity act;
Context ctx;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ctx = this;
act = this;
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.main);
preview = new Preview(this, (SurfaceView)findViewById(R.id.surfaceView));
preview.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
((FrameLayout) findViewById(R.id.layout)).addView(preview);
preview.setKeepScreenOn(true);
preview.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
camera.takePicture(shutterCallback, rawCallback, jpegCallback);
}
});
Toast.makeText(ctx, getString(R.string.take_photo_help), Toast.LENGTH_LONG).show();
// buttonClick = (Button) findViewById(R.id.btnCapture);
//
// buttonClick.setOnClickListener(new OnClickListener() {
// public void onClick(View v) {
//// preview.camera.takePicture(shutterCallback, rawCallback, jpegCallback);
// camera.takePicture(shutterCallback, rawCallback, jpegCallback);
// }
// });
//
// buttonClick.setOnLongClickListener(new OnLongClickListener(){
// @Override
// public boolean onLongClick(View arg0) {
// camera.autoFocus(new AutoFocusCallback(){
// @Override
// public void onAutoFocus(boolean arg0, Camera arg1) {
// //camera.takePicture(shutterCallback, rawCallback, jpegCallback);
// }
// });
// return true;
// }
// });
}
@Override
protected void onResume() {
super.onResume();
int numCams = Camera.getNumberOfCameras();
if(numCams > 0){
try{
camera = Camera.open(0);
camera.startPreview();
preview.setCamera(camera);
} catch (RuntimeException ex){
Toast.makeText(ctx, getString(R.string.camera_not_found), Toast.LENGTH_LONG).show();
}
}
}
@Override
protected void onPause() {
if(camera != null) {
camera.stopPreview();
preview.setCamera(null);
camera.release();
camera = null;
}
super.onPause();
}
private void resetCam() {
camera.startPreview();
preview.setCamera(camera);
}
private void refreshGallery(File file) {
Intent mediaScanIntent = new Intent( Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
mediaScanIntent.setData(Uri.fromFile(file));
sendBroadcast(mediaScanIntent);
}
ShutterCallback shutterCallback = new ShutterCallback() {
public void onShutter() {
// Log.d(TAG, "onShutter'd");
}
};
PictureCallback rawCallback = new PictureCallback() {
public void onPictureTaken(byte[] data, Camera camera) {
// Log.d(TAG, "onPictureTaken - raw");
}
};
PictureCallback jpegCallback = new PictureCallback() {
public void onPictureTaken(byte[] data, Camera camera) {
new SaveImageTask().execute(data);
resetCam();
Log.d(TAG, "onPictureTaken - jpeg");
}
};
private class SaveImageTask extends AsyncTask<byte[], Void, Void> {
@Override
protected Void doInBackground(byte[]... data) {
FileOutputStream outStream = null;
// Write to SD Card
try {
File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdCard.getAbsolutePath() + "/camtest");
dir.mkdirs();
String fileName = String.format("%d.jpg", System.currentTimeMillis());
File outFile = new File(dir, fileName);
outStream = new FileOutputStream(outFile);
outStream.write(data[0]);
outStream.flush();
outStream.close();
Log.d(TAG, "onPictureTaken - wrote bytes: " + data.length + " to " + outFile.getAbsolutePath());
refreshGallery(outFile);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
}
return null;
}
}
}
Preview.java
class Preview extends ViewGroup implements SurfaceHolder.Callback {
private final String TAG = "Preview";
SurfaceView mSurfaceView;
SurfaceHolder mHolder;
Size mPreviewSize;
List<Size> mSupportedPreviewSizes;
Camera mCamera;
Preview(Context context, SurfaceView sv) {
super(context);
mSurfaceView = sv;
// addView(mSurfaceView);
mHolder = mSurfaceView.getHolder();
mHolder.addCallback(this);
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void setCamera(Camera camera) {
mCamera = camera;
if (mCamera != null) {
mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
requestLayout();
// get Camera parameters
Camera.Parameters params = mCamera.getParameters();
List<String> focusModes = params.getSupportedFocusModes();
if (focusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO)) {
// set the focus mode
params.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);
// set Camera parameters
mCamera.setParameters(params);
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// We purposely disregard child measurements because act as a
// wrapper to a SurfaceView that centers the camera preview instead
// of stretching it.
final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
setMeasuredDimension(width, height);
if (mSupportedPreviewSizes != null) {
mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width, height);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (changed && getChildCount() > 0) {
final View child = getChildAt(0);
final int width = r - l;
final int height = b - t;
int previewWidth = width;
int previewHeight = height;
if (mPreviewSize != null) {
previewWidth = mPreviewSize.width;
previewHeight = mPreviewSize.height;
}
// Center the child SurfaceView within the parent.
if (width * previewHeight > height * previewWidth) {
final int scaledChildWidth = previewWidth * height / previewHeight;
child.layout((width - scaledChildWidth) / 2, 0,
(width + scaledChildWidth) / 2, height);
} else {
final int scaledChildHeight = previewHeight * width / previewWidth;
child.layout(0, (height - scaledChildHeight) / 2,
width, (height + scaledChildHeight) / 2);
}
}
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, acquire the camera and tell it where
// to draw.
try {
if (mCamera != null) {
mCamera.setPreviewDisplay(holder);
}
} catch (IOException exception) {
Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
// Surface will be destroyed when we return, so stop the preview.
if (mCamera != null) {
mCamera.stopPreview();
}
}
private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
final double ASPECT_TOLERANCE = 0.1;
double targetRatio = (double) w / h;
if (sizes == null) return null;
Size optimalSize = null;
double minDiff = Double.MAX_VALUE;
int targetHeight = h;
// Try to find an size match aspect ratio and size
for (Size size : sizes) {
double ratio = (double) size.width / size.height;
if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
// Cannot find the one match the aspect ratio, ignore the requirement
if (optimalSize == null) {
minDiff = Double.MAX_VALUE;
for (Size size : sizes) {
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
}
return optimalSize;
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
if(mCamera != null) {
Camera.Parameters parameters = mCamera.getParameters();
parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
requestLayout();
mCamera.setParameters(parameters);
mCamera.startPreview();
}
}
}
这是logcat。
12-15 15:10:10.010: E/AndroidRuntime(1857): FATAL EXCEPTION: main
12-15 15:10:10.010: E/AndroidRuntime(1857): Process: com.example.cam, PID: 1857
12-15 15:10:10.010: E/AndroidRuntime(1857): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.takePicture(android.hardware.Camera$ShutterCallback, android.hardware.Camera$PictureCallback, android.hardware.Camera$PictureCallback)' on a null object reference
12-15 15:10:10.010: E/AndroidRuntime(1857): at com.example.cam.CamTestActivity$4.onClick(CamTestActivity.java:62)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.view.View.performClick(View.java:4756)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.view.View$PerformClick.run(View.java:19749)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.os.Handler.handleCallback(Handler.java:739)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.os.Handler.dispatchMessage(Handler.java:95)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.os.Looper.loop(Looper.java:135)
12-15 15:10:10.010: E/AndroidRuntime(1857): at android.app.ActivityThread.main(ActivityThread.java:5221)
12-15 15:10:10.010: E/AndroidRuntime(1857): at java.lang.reflect.Method.invoke(Native Method)
12-15 15:10:10.010: E/AndroidRuntime(1857): at java.lang.reflect.Method.invoke(Method.java:372)
12-15 15:10:10.010: E/AndroidRuntime(1857): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
12-15 15:10:10.010: E/AndroidRuntime(1857): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
最佳答案
此错误的两个原因如下：
1）您尚未初始化相机：
mcamera = mcamera.open();
2）您尚未在androidmanifest.xml文件中授予权限。
<uses-permission android:name="android.permission.CAMERA"/>
关于android - 无法访问相机，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/27481101/