我有一个应用程序处理来自相机的帧并显示在布局上，捕获和管理相机帧的类如下：
package org.opencv.face;
import java.io.IOException;
import java.util.List;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.ImageFormat;
import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public abstract class SampleViewBase extends SurfaceView implements SurfaceHolder.Callback, Runnable {
private static final String TAG = "Sample::SurfaceView";
public Camera mCamera;
private SurfaceHolder mHolder;
private int mFrameWidth;
private int mFrameHeight;
private byte[] mFrame;
private boolean mThreadRun;
private byte[] mBuffer;
public SampleViewBase(Context context) {
super(context);
mHolder = getHolder();
mHolder.addCallback(this);
Log.i(TAG, "Instantiated new " + this.getClass());
}
public int getFrameWidth() {
return mFrameWidth;
}
public int getFrameHeight() {
return mFrameHeight;
}
public void setPreview() throws IOException {
mCamera.setPreviewDisplay(null);
}
public boolean openCamera() {
Log.i(TAG, "openCamera");
releaseCamera();
mCamera = Camera.open();
if(mCamera == null) {
Log.e(TAG, "Can't open camera!");
return false;
}
mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
public void onPreviewFrame(byte[] data, Camera camera) {
synchronized (SampleViewBase.this) {
System.arraycopy(data, 0, mFrame, 0, data.length);
SampleViewBase.this.notify();
}
camera.addCallbackBuffer(mBuffer);
}
});
return true;
}
public void releaseCamera() {
Log.i(TAG, "releaseCamera");
mThreadRun = false;
synchronized (this) {
if (mCamera != null) {
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
mCamera.release();
mCamera = null;
}
}
onPreviewStopped();
}
public void setupCamera(int width, int height) {
Log.i(TAG, "setupCamera");
synchronized (this) {
if (mCamera != null) {
Camera.Parameters params = mCamera.getParameters();
List<Camera.Size> sizes = params.getSupportedPreviewSizes();
mFrameWidth = width;
mFrameHeight = height;
// selecting optimal camera preview size
{
int minDiff = Integer.MAX_VALUE;
for (Camera.Size size : sizes) {
if (Math.abs(size.height - height) < minDiff) {
mFrameWidth = size.width;
mFrameHeight = size.height;
minDiff = Math.abs(size.height - height);
}
}
}
params.setPreviewSize(getFrameWidth(), getFrameHeight());
List<String> FocusModes = params.getSupportedFocusModes();
if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO))
{
params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);
}
mCamera.setParameters(params);
/* Now allocate the buffer */
params = mCamera.getParameters();
int size = params.getPreviewSize().width * params.getPreviewSize().height;
size = size * ImageFormat.getBitsPerPixel(params.getPreviewFormat()) / 8 * 2;
mBuffer = new byte[size];
/* The buffer where the current frame will be copied */
mFrame = new byte [size];
mCamera.addCallbackBuffer(mBuffer);
try {
setPreview();
} catch (IOException e) {
Log.e(TAG, "mCamera.setPreviewDisplay/setPreviewTexture fails: " + e);
}
/* Notify that the preview is about to be started and deliver preview size */
onPreviewStarted(params.getPreviewSize().width, params.getPreviewSize().height);
/* Now we can start a preview */
mCamera.startPreview();
}
}
}
public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
Log.i(TAG, "surfaceChanged");
setupCamera(width, height);
}
public void surfaceCreated(SurfaceHolder holder) {
Log.i(TAG, "surfaceCreated");
(new Thread(this)).start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
Log.i(TAG, "surfaceDestroyed");
releaseCamera();
}
/* The bitmap returned by this method shall be owned by the child and released in onPreviewStopped() */
protected abstract Bitmap processFrame(byte[] data);
/**
* This method is called when the preview process is being started. It is called before the first frame delivered and processFrame is called
* It is called with the width and height parameters of the preview process. It can be used to prepare the data needed during the frame processing.
* @param previewWidth - the width of the preview frames that will be delivered via processFrame
* @param previewHeight - the height of the preview frames that will be delivered via processFrame
*/
protected abstract void onPreviewStarted(int previewWidtd, int previewHeight);
/**
* This method is called when preview is stopped. When this method is called the preview stopped and all the processing of frames already completed.
* If the Bitmap object returned via processFrame is cached - it is a good time to recycle it.
* Any other resources used during the preview can be released.
*/
protected abstract void onPreviewStopped();
public void run() {
mThreadRun = true;
Log.i(TAG, "Starting processing thread");
while (mThreadRun) {
Bitmap bmp = null;
synchronized (this) {
try {
this.wait();
bmp = processFrame(mFrame);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if (bmp != null) {
Canvas canvas = mHolder.lockCanvas();
if (canvas != null) {
canvas.drawBitmap(bmp, (canvas.getWidth() - getFrameWidth()) / 2, (canvas.getHeight() - getFrameHeight()) / 2, null);
mHolder.unlockCanvasAndPost(canvas);
}
}
}
}
}
除了用以下方法替换方法“setPreview（）”之外，屏幕无法显示任何内容：
@TargetApi(11)
public void setPreview() throws IOException {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
mSf = new SurfaceTexture(10);
mCamera.setPreviewTexture( mSf );
}
else
mCamera.setPreviewDisplay(null);
现在可以正常使用，但只适用于3.0以上的Android版本，我想要的是适用于任何版本。
我该如何解决这个问题？
答案 0 :(得分：0)
如果您想接收预览回调，必须显示预览，使用带有非空参数的setPreviewDisplay()。该API旨在强制您在屏幕上显示此预览。任何允许您创建从未渲染的虚拟SurfaceView的解决方法可能无法在某些设备上或下次升级后使用。
在Honeycomb之前，可以在屏幕外创建预览SurfaceView（使其位置远离右侧），因此不会显示预览。这个错误后来修复了。
幸运的是，使用3+你可以使用setPreviewTexture()，平台无法强迫你实际显示纹理。