java - 如何在android中打开两个摄像头

Question

我有这个代码

package com.example.camera_test;

import android.app.Activity;
import android.hardware.Camera;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.FrameLayout;

public class MainActivity extends Activity {

    private Camera mCamera;
    private CameraPreview mPreview;
    private CameraPreview mPreview2;
    private String TAG = "Camera Test Application";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Create an instance of Camera
        mCamera = getCameraInstance();

        // Create our Preview view and set it as the content of our activity.
        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);

        Camera mCamera2 = openFrontFacingCameraGingerbread();

        mPreview2 = new CameraPreview(this, mCamera2);
        FrameLayout preview2 = (FrameLayout) findViewById(R.id.camera_preview2);
        preview2.addView(mPreview2);
    }

    @Override
    protected void onPause()
    {
        super.onPause();
        releaseCamera();              // release the camera immediately on pause event

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    /** A safe way to get an instance of the Camera object. */
    public static Camera getCameraInstance(){
        Camera c = null;
        try {
            c = Camera.open(); // attempt to get a Camera instance
        }
        catch (Exception e){
            // Camera is not available (in use or does not exist)
        }
        return c; // returns null if camera is unavailable
    }

    private void releaseCamera()
    {
        if (mCamera != null)
        {
            mCamera.release(); // release the camera for other applications
            mCamera = null;
        }

    }

    private Camera openFrontFacingCameraGingerbread() {
        int cameraCount = 0;
        Camera cam = null;
        Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
        cameraCount = Camera.getNumberOfCameras();
        for ( int camIdx = 0; camIdx < cameraCount; camIdx++ ) {
            Camera.getCameraInfo( camIdx, cameraInfo );
            if ( cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT  ) {
                try {
                    cam = Camera.open( camIdx );
                } catch (RuntimeException e) {
                    Log.e(TAG, "Camera failed to open: " + e.getLocalizedMessage());
                }
            }
        }

        return cam;
    }

}

package com.example.camera_test;

import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private String TAG = "Camera Test Applicaiton";

    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);
            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());
        }
    }
}

我如何修复在布局中使用两个摄像头

 03-09 22:19:48.408: E/Trace(682): error opening trace file: No such file or directory (2)
 03-09 22:19:50.369: D/AndroidRuntime(682): Shutting down VM
 03-09 22:19:50.369: W/dalvikvm(682): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
 03-09 22:19:50.439: E/AndroidRuntime(682): FATAL EXCEPTION: main
 03-09 22:19:50.439: E/AndroidRuntime(682): java.lang.NullPointerException