访问前置摄像头“绿屏”？

Question

我开发了一个android2.3项目，从ApiDemos复制示例代码“CameraPreview”，并在我的evo 4g手机上运行它，后置摄像头是正确的，当切换到前置摄像头时，屏幕是“绿屏”，这是怎么回事问题？

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// ----------------------------------------------------------------------

import java.io.IOException;
import java.util.List;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.hardware.Camera.Size;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.view.WindowManager;

public class CameraPreview extends Activity
{
    private Preview mPreview;
    Camera          mCamera;
    int             numberOfCameras;
    int             cameraCurrentlyLocked;

    // The first rear facing camera
    int             defaultCameraId;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        // Hide the window title.
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

        // Create a RelativeLayout container that will hold a SurfaceView,
        // and set it as the content of our activity.
        mPreview = new Preview(this);
        setContentView(mPreview);

        // Find the total number of cameras available
        numberOfCameras = Camera.getNumberOfCameras();

        // Find the ID of the default camera
        CameraInfo cameraInfo = new CameraInfo();
        for (int i = 0; i < numberOfCameras; i++)
        {
            Camera.getCameraInfo(i, cameraInfo);
            if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK)
            {
                defaultCameraId = i;
            }
        }
    }

    @Override
    protected void onResume()
    {
        super.onResume();

        // Open the default i.e. the first rear facing camera.
        mCamera = Camera.open();
        cameraCurrentlyLocked = defaultCameraId;
        mPreview.setCamera(mCamera);
    }

    @Override
    protected void onPause()
    {
        super.onPause();

        // Because the Camera object is a shared resource, it's very
        // important to release it when the activity is paused.
        if (mCamera != null)
        {
            mPreview.setCamera(null);
            mCamera.release();
            mCamera = null;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {

        // Inflate our menu which can gather user input for switching camera
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.camera_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        // Handle item selection
        switch (item.getItemId())
        {
            case R.id.switch_cam:
                // check for availability of multiple cameras
                if (numberOfCameras == 1)
                {
                    AlertDialog.Builder builder = new AlertDialog.Builder(this);
                    builder.setMessage(this.getString(R.string.camera_alert)).setNeutralButton("Close", null);
                    AlertDialog alert = builder.create();
                    alert.show();
                    return true;
                }

                // OK, we have multiple cameras.
                // Release this camera -> cameraCurrentlyLocked
                if (mCamera != null)
                {
                    mCamera.stopPreview();
                    mPreview.setCamera(null);
                    mCamera.release();
                    mCamera = null;
                }

                // Acquire the next camera and request Preview to reconfigure
                // parameters.
                mCamera = Camera.open((cameraCurrentlyLocked + 1)
                        % numberOfCameras);
                cameraCurrentlyLocked = (cameraCurrentlyLocked + 1)
                        % numberOfCameras;
                mPreview.switchCamera(mCamera);

                // Start the preview
                mCamera.startPreview();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}

// ----------------------------------------------------------------------

/**
 * A simple wrapper around a Camera and a SurfaceView that renders a centered
 * preview of the Camera to the surface. We need to center the SurfaceView
 * because not all devices have cameras that support preview sizes at the same
 * aspect ratio as the device's display.
 */
class Preview extends ViewGroup implements SurfaceHolder.Callback
{
    private final String    TAG = "Preview";

    SurfaceView             mSurfaceView;
    SurfaceHolder           mHolder;
    Size                    mPreviewSize;
    List<Size>              mSupportedPreviewSizes;
    Camera                  mCamera;

    Preview(Context context)
    {
        super(context);

        mSurfaceView = new SurfaceView(context);
        addView(mSurfaceView);

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = mSurfaceView.getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void setCamera(Camera camera)
    {
        mCamera = camera;
        if (mCamera != null)
        {
            mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
            requestLayout();
        }
    }

    public void switchCamera(Camera camera)
    {
        setCamera(camera);
        try
        {
            camera.setPreviewDisplay(mHolder);
        } 
        catch (IOException exception)
        {
            Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
        }
        Camera.Parameters parameters = camera.getParameters();
        parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
        requestLayout();

        camera.setParameters(parameters);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        // We purposely disregard child measurements because act as a
        // wrapper to a SurfaceView that centers the camera preview instead
        // of stretching it.
        final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);

        if (mSupportedPreviewSizes != null)
        {
            mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width, height);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b)
    {
        if (changed && getChildCount() > 0)
        {
            final View child = getChildAt(0);

            final int width = r - l;
            final int height = b - t;

            int previewWidth = width;
            int previewHeight = height;
            if (mPreviewSize != null)
            {
                previewWidth = mPreviewSize.width;
                previewHeight = mPreviewSize.height;
            }

            // Center the child SurfaceView within the parent.
            if (width * previewHeight > height * previewWidth)
            {
                final int scaledChildWidth = previewWidth * height
                        / previewHeight;
                child.layout((width - scaledChildWidth) / 2, 0, (width + scaledChildWidth) / 2, height);
            } else
            {
                final int scaledChildHeight = previewHeight * width
                        / previewWidth;
                child.layout(0, (height - scaledChildHeight) / 2, width, (height + scaledChildHeight) / 2);
            }
        }
    }

    public void surfaceCreated(SurfaceHolder holder)
    {
        // The Surface has been created, acquire the camera and tell it where
        // to draw.
        try
        {
            if (mCamera != null)
            {
                mCamera.setPreviewDisplay(holder);
            }
        } catch (IOException exception)
        {
            Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder)
    {
        // Surface will be destroyed when we return, so stop the preview.
        if (mCamera != null)
        {
            mCamera.stopPreview();
        }
    }

    private Size getOptimalPreviewSize(List<Size> sizes, int w, int h)
    {
        final double ASPECT_TOLERANCE = 0.1;
        double targetRatio = (double) w / h;
        if (sizes == null)
            return null;

        Size optimalSize = 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)
            {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        // Cannot find the one match the aspect ratio, ignore the requirement
        if (optimalSize == null)
        {
            minDiff = Double.MAX_VALUE;
            for (Size size : sizes)
            {
                if (Math.abs(size.height - targetHeight) < minDiff)
                {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }
        return optimalSize;
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h)
    {
        // Now that the size is known, set up the camera parameters and begin
        // the preview.
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
        requestLayout();

        mCamera.setParameters(parameters);
        mCamera.startPreview();
    }

}


AndroidManifest.xml

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.kiterive.magicmirror"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="9" />
    <!-- We will request access to the camera, saying we require a camera
         of some sort but not one with autofocus capability. -->
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-feature android:name="android.hardware.camera" />
    <uses-feature android:name="android.hardware.camera.autofocus" android:required="false" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MagicMirrorActivity"
                  android:label="@string/app_name"
                  android:screenOrientation="landscape">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
</manifest>

Answer 1

EVO 4G（截至撰写本文时）运行 Android 2.2，缺乏对 2.3 前置摄像头 API 的支持。我很惊讶您的代码示例运行时没有引发您正在调用的 2.3 API 调用的异常。

Answer 2

很可能是设备问题、驱动程序问题或其他问题。
尝试在另一台设备上测试它。
另请确保设备运行的是 Android 2.3 或更高版本，低于该版本的设备不受支持。