我正在创建一个在相机预览上显示动态图片的应用程序。我这样做的方式是在我的主要活动内的框架布局中添加两个 SurfaceView，一个持有相机预览，一个持有我的动态图片。所以基本上有3个公共类，还有一个动图类里面的内线程类来控制动画。
它在启动应用程序时运行良好 - 相机正在预览并且图片正在移动。但是，如果我暂停活动，通过转到主屏幕或通过单击图片重定向到另一个活动，然后继续，相机预览会变黑。奇怪的是，如果我将手机旋转到不同的模式（横向/纵向），事情就会恢复正常。
我已经阅读了几篇关于相机无法恢复的帖子，但解决方案都是关于打开相机。经过检查，我很确定我的问题与相机实例无关。实际上，如果我通过转到主屏幕来暂停活动，当我恢复时，相机会出现一秒钟然后黑屏。
我一直在尝试各种事情，包括在 OnPause() 中从我的布局中删除所有视图，并在添加视图时指定索引号。但唯一取得一点进展的方法是我在下面的代码块中注释掉画布锁。没有锁，图片会随机移动，但相机可以恢复。事实上，如果我忽略所有关于线程的事情，只显示一张静态图片，相机也可以正常工作。所以我感觉到我的线程有问题，但我无法弄清楚。
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()
}
这是完成线程的部分：
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();
}
}
[/更新]
[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;
}
}
[/更新2]
我发现的另一件事是，当我暂停活动时，很少执行解锁。虽然当它被执行时相机仍然没有回来，但这种行为对我来说似乎很奇怪，因为 thread.join() 被执行所以我认为 finally 块也应该被执行。
抱歉，我无法用更少的词来描述我的问题，但请留下您的任何线索。提前致谢！