我正在尝试将Android 开发人员指南中定义的 CameraPreview 放到 ApiDemos/OS/Sensors 应用程序屏幕上。一半的时间按预期工作。但是，每隔一次我恢复这个测试应用程序（假设我通过按下设备的“主页”图标暂停它）都会记录以下异常：
06-13 14:10:17.369: D/SENSORS_TEST(11888): 支持的预览宽度 x 高度: 640 x 480 06-13 14:10:17.369: D/SENSORS_TEST(11888): 支持的预览宽度 x 高度: 320 x 240 06-13 14:10:17.369: D/SENSORS_TEST(11888): 支持的预览宽度 x 高度: 176 x 144 06-13 14:10:17.600: D/dalvikvm(11888): GC_FOR_ALLOC 释放 56K，3% 释放 9091K/ 9347K，暂停 22 毫秒 06-13 14:10:17.600：I/dalvikvm-heap(11888)：将堆（碎片情况）增加到 9.610MB，分配 695056 字节 06-13 14:10:17.631：D/dalvikvm(11888 ): GC_CONCURRENT 释放 1K, 3% 空闲 9768K/10055K, 暂停 2ms+2ms 06-13 14:10:31.510: D/AndroidRuntime(11888): 关闭 VM 06-13 14:10:31.510: W/dalvikvm(11888 ）：threadid = 1：线程以未捕获的异常退出（组= 0x40a351f8）06-13 14：10：31.518：E / AndroidRuntime（11888）：致命异常：主要06-13 14：10：31.518：E/AndroidRuntime(11888): java.lang.RuntimeException: 释放后调用的方法() 06-13 14:10:31.518: E/AndroidRuntime(11888): at android.hardware.Camera.setPreviewDisplay(Native Method) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.hardware.Camera.setPreviewDisplay(Camera.java:405) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在com.example.sensor.Sensors10Activity$CameraPreview.surfaceCreated(Sensors10Activity.java:221)
06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.view.SurfaceView.updateWindow(SurfaceView.java:533) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android. view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:226) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.view.View.dispatchWindowVisibilityChanged(View.java:5839) 06-13 14:10: 31.518: E/AndroidRuntime(11888): 在 android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:945) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup .java:945) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:945) 06-13 14:10:31.518: E/AndroidRuntime(11888 ): 在 android.view.ViewGroup。dispatchWindowVisibilityChanged(ViewGroup.java:945) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:965) 06-13 14:10:31.518: E/ AndroidRuntime(11888): 在 android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.os.Handler.dispatchMessage(Handler.java:99 ) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android.os.Looper.loop(Looper.java:137) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 android .app.ActivityThread.main(ActivityThread.java:4424) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 java.lang.reflect.Method.invokeNative(Native Method) 06-13 14:10: 31.518: E/AndroidRuntime(11888): 在 java.lang.reflect.Method.invoke(Method.java:511) 06-13 14:10:31.518: E/AndroidRuntime(11888):在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 06-13 14:10:31.518: E/AndroidRuntime(11888): 在 com.android.internal.os.ZygoteInit.main( ZygoteInit.java:551) 06-13 14:10:31.518: E/AndroidRuntime(11888): at dalvik.system.NativeStart.main(Native Method)
这是代码，大部分代码直接取自开发指南的相机示例和 ApiDemos/OS/Sensors 示例。有没有人看到在 Activity 生命周期中应该做些什么来避免在第 221 行发生的异常（如代码中所述）？
提前感谢您的检查，
格雷格
public class Sensors10Activity extends Activity {
private final String TAG = "SENSORS_TEST";
private SensorManager mSensorManager;
private GraphView mGraphView;
private Camera mCamera;
private CameraPreview mCameraPreview;
public class GraphView extends View implements SensorEventListener {
private Bitmap mBitmap;
private Paint mPaint = new Paint();
private Canvas mCanvas = new Canvas();
private Path mPath = new Path();
private RectF mRect = new RectF();
private float mLastValues[] = new float[3*2];
private float mOrientationValues[] = new float[3];
private int mColors[] = new int[3*2];
private float mLastX;
private float mScale[] = new float[2];
private float mYOffset;
private float mMaxX;
private float mSpeed = 1.0f;
private float mWidth;
private float mHeight;
public GraphView(Context context) {
super(context);
mColors[0] = Color.argb(192, 255, 64, 64);
mColors[1] = Color.argb(192, 64, 128, 64);
mColors[2] = Color.argb(192, 64, 64, 255);
mColors[3] = Color.argb(192, 64, 255, 255);
mColors[4] = Color.argb(192, 128, 64, 128);
mColors[5] = Color.argb(192, 255, 255, 64);
mPaint.setFlags(Paint.ANTI_ALIAS_FLAG);
mRect.set(-0.5f, -0.5f, 0.5f, 0.5f);
mPath.arcTo(mRect, 0, 180);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.RGB_565);
mCanvas.setBitmap(mBitmap);
mCanvas.drawColor(0xFFFFFFFF);
mYOffset = h * 0.5f;
mScale[0] = - (h * 0.5f * (1.0f / (SensorManager.STANDARD_GRAVITY * 2)));
mScale[1] = - (h * 0.5f * (1.0f / (SensorManager.MAGNETIC_FIELD_EARTH_MAX)));
mWidth = w;
mHeight = h;
if (mWidth < mHeight) {
mMaxX = w;
} else {
mMaxX = w-50;
}
mLastX = mMaxX;
super.onSizeChanged(w, h, oldw, oldh);
}
@Override
protected void onDraw(Canvas canvas) {
synchronized (this) {
if (mBitmap != null) {
final Paint paint = mPaint;
final Path path = mPath;
final int outer = 0xFFC0C0C0;
final int inner = 0xFFff7010;
if (mLastX >= mMaxX) {
mLastX = 0;
final Canvas cavas = mCanvas;
final float yoffset = mYOffset;
final float maxx = mMaxX;
final float oneG = SensorManager.STANDARD_GRAVITY * mScale[0];
paint.setColor(0xFFAAAAAA);
cavas.drawColor(0xFFFFFFFF);
cavas.drawLine(0, yoffset, maxx, yoffset, paint);
cavas.drawLine(0, yoffset+oneG, maxx, yoffset+oneG, paint);
cavas.drawLine(0, yoffset-oneG, maxx, yoffset-oneG, paint);
}
canvas.drawBitmap(mBitmap, 0, 0, null);
float[] values = mOrientationValues;
if (mWidth < mHeight) {
float w0 = mWidth * 0.333333f;
float w = w0 - 32;
float x = w0*0.5f;
for (int i=0 ; i<3 ; i++) {
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.translate(x, w*0.5f + 4.0f);
canvas.save(Canvas.MATRIX_SAVE_FLAG);
paint.setColor(outer);
canvas.scale(w, w);
canvas.drawOval(mRect, paint);
canvas.restore();
canvas.scale(w-5, w-5);
paint.setColor(inner);
canvas.rotate(-values[i]);
canvas.drawPath(path, paint);
canvas.restore();
x += w0;
}
} else {
float h0 = mHeight * 0.333333f;
float h = h0 - 32;
float y = h0*0.5f;
for (int i=0 ; i<3 ; i++) {
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.translate(mWidth - (h*0.5f + 4.0f), y);
canvas.save(Canvas.MATRIX_SAVE_FLAG);
paint.setColor(outer);
canvas.scale(h, h);
canvas.drawOval(mRect, paint);
canvas.restore();
canvas.scale(h-5, h-5);
paint.setColor(inner);
canvas.rotate(-values[i]);
canvas.drawPath(path, paint);
canvas.restore();
y += h0;
}
}
}
}
}
public void onSensorChanged(SensorEvent event) {
//Log.d(TAG, "sensor: " + sensor + ", x: " + values[0] + ", y: " + values[1] + ", z: " + values[2]);
synchronized (this) {
if (mBitmap != null) {
final Canvas canvas = mCanvas;
final Paint paint = mPaint;
if (event.sensor.getType() == Sensor.TYPE_ORIENTATION) {
for (int i=0 ; i<3 ; i++) {
mOrientationValues[i] = event.values[i];
}
} else {
float deltaX = mSpeed;
float newX = mLastX + deltaX;
int j = (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) ? 1 : 0;
for (int i=0 ; i<3 ; i++) {
int k = i+j*3;
final float v = mYOffset + event.values[i] * mScale[j];
paint.setColor(mColors[k]);
canvas.drawLine(mLastX, mLastValues[k], newX, v, paint);
mLastValues[k] = v;
}
if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
mLastX += mSpeed;
}
invalidate();
}
}
}
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
}
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
// 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); // !!! LINE 221: exception occurs here.
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());
}
}
}
//////////////
// LIFE CYCLE
//
/**
* Initialization of the Activity after it is first created. Must at least
* call {@link android.app.Activity#setContentView setContentView()} to
* describe what is to be displayed in the screen.
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
// Be sure to call the super class.
super.onCreate(savedInstanceState);
mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
mCamera = Camera.open(1);
mCameraPreview = new CameraPreview(this, mCamera);
mGraphView = new GraphView(this);
// setContentView(mGraphView);
// Create RelativeLayout for layout root.
RelativeLayout relativeLayout = new RelativeLayout(this);
RelativeLayout.LayoutParams rlp = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.FILL_PARENT,
RelativeLayout.LayoutParams.FILL_PARENT);
// Add GraphView to layout.
RelativeLayout.LayoutParams lpGraph = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.FILL_PARENT,
RelativeLayout.LayoutParams.FILL_PARENT);
mGraphView.setLayoutParams(lpGraph);
relativeLayout.addView(mGraphView);
// Add SurfaceView to layout.
List<Camera.Size> ls = mCamera.getParameters().getSupportedPreviewSizes();
int n = ls.size();
int widthMin = 10000;
int imin = -1;
for (int i=0; i<n; i++) {
Log.d(TAG, "supported preview width x height: " + ls.get(i).width + " x " + ls.get(i).height);
if (widthMin > ls.get(i).width) {
widthMin = ls.get(i).width;
imin = i;
}
}
if (imin >= 0) {
RelativeLayout.LayoutParams lpSurface = new RelativeLayout.LayoutParams(
ls.get(imin).width, ls.get(imin).height);
lpSurface.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
lpSurface.addRule(RelativeLayout.CENTER_HORIZONTAL);
mCameraPreview.setLayoutParams(lpSurface);
relativeLayout.addView(mCameraPreview);
}
// Provide Android framework with layout root.
setContentView(relativeLayout, rlp);
}
@Override
protected void onResume() {
super.onResume();
mSensorManager.registerListener(mGraphView,
mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
SensorManager.SENSOR_DELAY_FASTEST);
mSensorManager.registerListener(mGraphView,
mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD),
SensorManager.SENSOR_DELAY_FASTEST);
mSensorManager.registerListener(mGraphView,
mSensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION),
SensorManager.SENSOR_DELAY_FASTEST);
if (mCamera == null)
mCamera = Camera.open(1);
if (mCameraPreview == null)
mCameraPreview = new CameraPreview(this, mCamera);
}
@Override
protected void onPause() {
super.onPause();
if (mCamera != null) {
mCamera.stopPreview();
mCamera.release(); // release the camera for other applications
mCamera = null;
}
if (mCameraPreview != null) {
mCameraPreview = null;
}
}
@Override
protected void onStop() {
mSensorManager.unregisterListener(mGraphView);
super.onStop();
}
}