我正在Android App中的后台拍照。但它会出错：
02-09 15:22:12.061: E/cheeta(28633): timer testing
02-09 15:22:13.546: W/System.err(28633): java.lang.RuntimeException: takePicture failed
02-09 15:22:13.546: W/System.err(28633): at android.hardware.Camera.native_takePicture(Native Method)
02-09 15:22:13.546: W/System.err(28633): at android.hardware.Camera.takePicture(Camera.java:1194)
02-09 15:22:13.551: W/System.err(28633): at cam.sharp.MainActivity$MyTimerTask.run(MainActivity.java:69)
02-09 15:22:13.551: W/System.err(28633): at java.util.Timer$TimerImpl.run(Timer.java:284)
02-09 15:22:13.551: E/cheeta(28633): timer testing
02-09 15:22:15.051: W/System.err(28633): java.lang.RuntimeException: takePicture failed
02-09 15:22:15.051: W/System.err(28633): at android.hardware.Camera.native_takePicture(Native Method)
02-09 15:22:15.051: W/System.err(28633): at android.hardware.Camera.takePicture(Camera.java:1194)
02-09 15:22:15.051: W/System.err(28633): at cam.sharp.MainActivity$MyTimerTask.run(MainActivity.java:69)
02-09 15:22:15.051: W/System.err(28633): at java.util.Timer$TimerImpl.run(Timer.java:284)
02-09 15:22:15.051: E/cheeta(28633): timer testing
02-09 15:22:16.551: W/System.err(28633): java.lang.RuntimeException: takePicture failed
02-09 15:22:16.556: W/System.err(28633): at android.hardware.Camera.native_takePicture(Native Method)
02-09 15:22:16.556: W/System.err(28633): at android.hardware.Camera.takePicture(Camera.java:1194)
02-09 15:22:16.561: W/System.err(28633): at cam.sharp.MainActivity$MyTimerTask.run(MainActivity.java:69)
02-09 15:22:16.561: W/System.err(28633): at java.util.Timer$TimerImpl.run(Timer.java:284)
02-09 15:22:16.561: E/cheeta(28633): timer testing
我有两个文件。
MainActivity.java和CameraPreview.java
以下是两者的代码。
MainActivity.java
package cam.sharp;
import java.io.File;
import java.io.FileOutputStream;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.content.Context;
import android.hardware.Camera;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.widget.FrameLayout;
import android.widget.Toast;
public class MainActivity extends Activity {
private int cameraId = 0;
private Camera mCamera;
private CameraPreview mPreview;
String fileName = "tempImage.jpeg";
File file;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create an instance of Camera
mCamera = getCameraInstance(cameraId);
if (mCamera == null) {
Toast.makeText(
getApplicationContext(),
"The camera service is currently unavailable, please try again!",
Toast.LENGTH_LONG).show();
finish();
} else {
// Create our Preview view and set it as the content of our
// activity.
mPreview = new CameraPreview(this, mCamera);
FrameLayout frameLayout = (FrameLayout) findViewById(R.id.camera_preview);
frameLayout.addView(mPreview);
}
// start thread for these
MyTimerTask myTask = new MyTimerTask();
Timer myTimer = new Timer();
// public void schedule (TimerTask task, long delay, long period)
// Schedule a task for repeated fixed-delay execution after a specific
// delay.
//
// Parameters
// task the task to schedule.
// delay amount of time in milliseconds before first execution.
// period amount of time in milliseconds between subsequent executions.
myTimer.schedule(myTask, 3000, 1500);
}
class MyTimerTask extends TimerTask {
public void run() {
try {
mCamera.takePicture(null, null, null, mPictureCallback);
file = new File(getFilesDir(), fileName);
} catch (Exception e) {
e.printStackTrace();
}
Log.e("cheeta", "timer testing");
}
}
Camera.PictureCallback mPictureCallback = new Camera.PictureCallback() {
public void onPictureTaken(byte[] imageData, Camera c) {
Log.e("Callback TAG", "Here in jpeg Callback");
if (imageData != null) {
FileOutputStream outputStream;
try {
outputStream = openFileOutput(fileName,
Context.MODE_PRIVATE);
outputStream.write(imageData);
outputStream.close();
// Intent intent = new Intent(SnapScreen.this,
// PreviewScreen.class);
// if (fromMessageReview == true) {
// intent.putExtra("fromMessageReview", "true");
// }
// startActivity(intent);
// overridePendingTransition(R.anim.slide_in,
// R.anim.slide_out);
finish();
} catch (Exception e) {
e.printStackTrace();
}
}
}
};
@Override
protected void onDestroy() {
super.onDestroy();
releaseCamera();
}
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(int cameraId) {
Camera c = null;
try {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) {
c = Camera.open(cameraId);
} else {
c = Camera.open();
}
} catch (Exception e) {
c = null;
}
return c; // returns null if camera is unavailable
}
private void releaseCamera() {
if (mCamera != null) {
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
}
CameraPreview.java
package cam.sharp;
import java.io.IOException;
import android.annotation.SuppressLint;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
/** A basic Camera preview class */
@SuppressLint("ViewConstructor")
public class CameraPreview extends SurfaceView implements
SurfaceHolder.Callback {
private static final String TAG = "Camera Preview";
private SurfaceHolder mHolder;
public Camera mCamera;
@SuppressWarnings("deprecation")
@SuppressLint("NewApi")
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
mCamera.setDisplayOrientation(90);
// 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) {
// The Surface has been created, now tell the camera where to draw the
// preview.
try {
mCamera.setPreviewDisplay(holder);
mCamera.setDisplayOrientation(90);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
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) {
// 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 {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e) {
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
}
任何人都可以看到问题是什么？我打电话给 mCamera.startPreview（）; ，但仍无用。
由于
答案 0 :(得分：6)
您的代码中有2个问题：
首先：在您的onPictureTaken回拨中，您正在调用finish()方法，而这反过来表示应该销毁该活动，并调用onDestroy()方法，然后释放你的相机。但是你的MainActivity.java没有被销毁（不确定为什么，但是通过logCat，我发现onCreate()只被调用一次，所以我认为活动没有被销毁。可能的解释可能因为Timer是由一个不同的线程控制的，因此可能不知道MainActivity被销毁，但我无法确认），所以你的myTimer将继续运行，当它到达{ {1}}它会抛出一个mCamera.takePicture(null, null, null, mPictureCallback);因为相机已经被释放了，并且没有再次调用NullPointException来获取mCamera的新实例。
所以，解决第一个问题：
MainActivity.onCreate() 第二：您在哪里调用Camera.PictureCallback mPictureCallback = new Camera.PictureCallback() {
public void onPictureTaken(byte[] imageData, Camera c) {
Log.e("Callback TAG", "Here in jpeg Callback");
if (imageData != null) {
FileOutputStream outputStream = null;
try {
outputStream = openFileOutput(fileName, Context.MODE_PRIVATE);
outputStream.write(imageData);
// Removed the finish call you had here
} catch (Exception e) {
e.printStackTrace();
} finally {
if (outputStream != null) try {
outputStream.close();
} catch (IOException ex) {
// TODO Auto-generated catch block
ex.printStackTrace();
}
}
}
}
};
方法。根据{{1}}：
此方法仅在预览处于活动状态时有效（之后 startPreview（））。拍摄图像后将停止预览; 如果要重新启动，调用者必须再次调用startPreview（） 预览或拍摄更多照片。这不应该在两者之间调用 start（）和stop（）。
您在创建相机时只调用了startPreview()一次，并且由于问题1，MainActivity上的takePicture()仅被调用一次。由于你有一个定时器每1.5秒拍照，你应该在致电startPreview()之前致电onCreate()，以解决这个问题：
startPreview()在此之后，应用程序继续拍照并存储它们。我从来没有使用像这样的计时器，所以我不知道如何让它停止。如果您只想在takePicture()的每次调用中拍摄少量照片，我建议您使用带有动作监听器的Timer，如下所示：
class MyTimerTask extends TimerTask {
public void run() {
try {
// Call startPreview before taking a picture
mCamera.startPreview();
mCamera.takePicture(null, null, null, mPictureCallback);
file = new File(getFilesDir(), fileName);
} catch (NullPointerException ne) {
ne.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Log.e("cheeta", "timer testing");
}
}