前置摄像头不工作，抛出IllegalStateException

Question

java.lang.IllegalStateException：无法执行活动的方法

引起：java.lang.reflect.InvocationTargetException

引起：java.lang.RuntimeException：takePicture失败

以下是我的MainActivity，名为One：

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Created by Poorvi on 4/30/2016.
 */
public class One extends Activity {

    private final static String DEBUG_TAG = "MakePhotoActivity";
    private Camera camera;
    private int cameraId = 0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.one);

        // do we have a camera?
        if (!getPackageManager()
                .hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
            Toast.makeText(this, "No camera on this device", Toast.LENGTH_LONG)
                    .show();
        } else {
            cameraId = findFrontFacingCamera();
            if (cameraId < 0) {
                Toast.makeText(this, "No front facing camera found.",
                        Toast.LENGTH_LONG).show();
            } else {
                camera = Camera.open(cameraId);
            }
        }
    }

    public void onClick(View view) {
        camera.takePicture(null, null,
                new PhotoHandler(getApplicationContext()));
    }

    private int findFrontFacingCamera() {
        int cameraId = -1;
        // Search for the front facing camera
        int numberOfCameras = Camera.getNumberOfCameras();
        for (int i = 0; i < numberOfCameras; i++) {
            Camera.CameraInfo info = new Camera.CameraInfo();
            Camera.getCameraInfo(i, info);
            if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
                Log.d(DEBUG_TAG, "Camera found");
                cameraId = i;
                break;
            }
        }
        return cameraId;
    }

    @Override
    protected void onPause() {
        if (camera != null) {
            camera.release();
            camera = null;
        }
        super.onPause();
    }

}

以下是我的PhotoHandler.java类：

import java.io.File;
import java.io.FileOutputStream;
import java.text.SimpleDateFormat;
import java.util.Date;

import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.os.Environment;
import android.util.Log;
import android.widget.Toast;

public class PhotoHandler implements PictureCallback {

    private final Context context;

    public PhotoHandler(Context context) {
        this.context = context;
    }

    @Override
    public void onPictureTaken(byte[] data, Camera camera) {

        File pictureFileDir = getDir();

        if (!pictureFileDir.exists() && !pictureFileDir.mkdirs()) {


            Toast.makeText(context, "Can't create directory to save image.",
                    Toast.LENGTH_LONG).show();
            return;

        }

        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyymmddhhmmss");
        String date = dateFormat.format(new Date());
        String photoFile = "Picture_" + date + ".jpg";

        String filename = pictureFileDir.getPath() + File.separator + photoFile;

        File pictureFile = new File(filename);

        try {
            FileOutputStream fos = new FileOutputStream(pictureFile);
            fos.write(data);
            fos.close();
            Toast.makeText(context, "New Image saved:" + photoFile,
                    Toast.LENGTH_LONG).show();
        } catch (Exception error) {

            Toast.makeText(context, "Image could not be saved.",
                    Toast.LENGTH_LONG).show();
        }
    }

    private File getDir() {
        File sdDir = Environment
                .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
        return new File(sdDir, "CameraAPIDemo");
    }
}