我正在创建一个应用程序，可在相机预览之上显示动态图像。我这样做的方法是在我的主要活动中的framelayout中添加两个SurfaceView，一个拿着相机预览，一个拿着我的动画。所以基本上有三个公共类，一个内部线程类在运动图片类中来控制动画。
启动应用程序时工作正常 - 相机正在预览，图片正在移动。但是然后如果我暂停活动，通过进入主屏幕或通过点击图片重定向到另一个活动，然后恢复，相机预览就会变黑。如果我旋转手机那么奇怪的部分就是进入一个不同的模式（风景/肖像），事情恢复正常。
我读过几篇关于相机没有恢复的文章，但解决方案都是关于打开相机。我非常确定我的问题与检查后的相机实例无关。实际上，如果我通过进入主屏幕暂停活动，当我恢复时，相机会出现一秒钟然后变黑。
我一直在尝试各种各样的事情，包括在OnPause（）中删除布局中的所有视图，并在添加视图时指定索引号。但是，当我在下面的块中注释掉画布锁时，唯一有点进步的方法。如果没有锁定，图片会随机移动，但相机可以恢复。事实上，如果我省略了关于线程的所有事情并且只显示静态图片，那么相机也可以正常工作。所以我觉得我的帖子出了问题，但我想不出来。
这是线程的运行方法：
public void run() {
Canvas canvas;
while (isRunning) { //When setRunning(false) occurs, isRunning is
canvas = null; //set to false and loop ends, stopping thread
try {
canvas = surfaceHolder.lockCanvas(null); //Lock
synchronized (surfaceHolder) {
//Insert methods to modify positions of items in onDraw()
animation();
postInvalidate();
}
} finally {
if (canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas); //Unlock
}
}
}
}
这是开始线程的部分：
public void surfaceCreated(SurfaceHolder arg0) {
setWillNotDraw(false); //Allows us to use invalidate() to call onDraw()
thread = new BubbleThread(getHolder(), this); //Start the thread that
thread.setRunning(true); //will make calls to
thread.start(); //onDraw()
}
这是完成主题的部分：
public void surfaceDestroyed(SurfaceHolder arg0) {
try {
thread.setRunning(false); //Tells thread to stop
thread.join(); //Removes thread from mem.
} catch (InterruptedException e) {}
}
[更新]主要活动代码：
public class MainActivity extends Activity {
... // Declarations
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
/* Adjust app settings */
...
//Load();
}
public void Load(){
/* Try to get the camera */
Camera c = getCameraInstance();
/* If the camera was received, create the app */
if (c != null){
// Create the parent layout to layer the
// camera preview and bubble layer
parentLayout = new FrameLayout(this);
parentLayout.setLayoutParams(new LayoutParams(
LayoutParams.MATCH_PARENT,
LayoutParams.MATCH_PARENT));
// Create a new camera view and add it to the layout
cameraPreview = new CameraPreview(this, c);
parentLayout.addView(cameraPreview, 0);
// Create a new draw view and add it to the layout
bubbleLayer = new BubbleLayer(this);
parentLayout.addView(bubbleLayer, 1);
// Set the layout as the apps content view
setContentView(parentLayout);
}
/* If the camera was not received, close the app */
else {
Toast toast = Toast.makeText(getApplicationContext(),
"Unable to find camera. Closing.", Toast.LENGTH_SHORT);
toast.show();
finish();
}
}
/** A safe way to get an instance of the Camera object. */
/** This method is strait from the Android API */
public static Camera getCameraInstance(){
Camera c = null;
try {
// Attempt to get a Camera instance
c = Camera.open();
}
catch (Exception e){
// Camera is not available (in use or does not exist)
e.printStackTrace();
}
return c;
}
/* Override the onPause method so that we
* can release the camera when the app is closing.
*/
@Override
protected void onPause() {
super.onPause();
if (cameraPreview != null){
cameraPreview.onPause();
cameraPreview = null;
}
}
/* We call Load in our Resume method, because
* the app will close if we call it in onCreate
*/
@Override
protected void onResume(){
super.onResume();
Load();
}
}
[/ UPDATE]
[UPDATE2]相机预览代码：
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
... // Declarations
public CameraPreview(Context context, Camera camera) {
super(context);
this.context = 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);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
Camera.Parameters parameters = mCamera.getParameters();
Size bestSize = getBestSize(parameters.getSupportedPreviewSizes(),
width,height);
parameters.setPreviewSize(bestSize.width, bestSize.height);
mCamera.setParameters(parameters);
// 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);
setCameraDisplayOrientation();
mCamera.startPreview();
} catch (Exception e){
Log.d("CameraView", "Error starting camera preview: "
+ e.getMessage());
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the
// camera where to draw the preview.
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d("CameraView", "Error setting camera preview: "
+ e.getMessage());
}
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// empty. Take care of releasing the Camera preview in your activity.
}
/* Find the best size for camera */
private Size getBestSize(List<Size> sizes, int w, int h) {
final double ASPECT_TOLERANCE = 0.05;
double targetRatio = (double) w / h;
if (sizes == null) return null;
Size bestSize = 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) {
bestSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
// Cannot find the one match the aspect ratio, ignore the requirement
if (bestSize == null) {
minDiff = Double.MAX_VALUE;
for (Size size : sizes) {
if (Math.abs(size.height - targetHeight) < minDiff) {
bestSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
}
return bestSize;
}
private void setCameraDisplayOrientation() {
if (mCamera == null) return;
Camera.CameraInfo info = new Camera.CameraInfo();
Camera.getCameraInfo(0, info);
WindowManager winManager = (WindowManager)
context.getSystemService(Context.WINDOW_SERVICE);
int rotation = winManager.getDefaultDisplay().getRotation();
int degrees = 0;
switch (rotation) {
case Surface.ROTATION_0: degrees = 0; break;
case Surface.ROTATION_90: degrees = 90; break;
case Surface.ROTATION_180: degrees = 180; break;
case Surface.ROTATION_270: degrees = 270; break;
}
int result;
if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
result = (info.orientation + degrees) % 360;
result = (360 - result) % 360; // compensate the mirror
}
else { // back-facing
result = (info.orientation - degrees + 360) % 360;
}
mCamera.setDisplayOrientation(result);
}
public void onPause() {
if (mCamera == null) return;
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}
[/ UPDATE2]
我发现的另一件事是，当我暂停活动时，解锁很少被执行。虽然当它被执行时摄像头仍然没有回来，但是这种行为对我来说似乎很奇怪，因为执行了thread.join（）所以我认为finally块也应该已经执行了。
抱歉，我不能用较少的话语来表达我的问题，但请留下任何线索。提前谢谢！
答案 0 :(得分：3)
我仍然不确切知道我的程序出了什么问题。但是在研究之后，我发现SurfaceView的z顺序似乎并不遵循正常的规则。因此，我没有使用两个SurfaceViews，一个用于相机，一个用于绘图，我切换到使用一个SurfaceView，现在它工作正常。
但是根据我的实验，无论是哪种实现，在屏幕上绘制相机预览都是一个缓慢的实现，因为线程之间的所有切换。所以人们应该尽量避免在设计中这样做......