android - 从 MainActivity 使用 Camera API SurfaceView 直接打开 Activity 时出错

Question

我有一个 MainActivity，它仅在电话号码未在共享首选项中设置时使用。在不需要 MainActivity 并且每次用户打开应用程序时设置电话号码后，他应该转到 CameraActivity Activity，其中有在 SurfaceView 中工作的 Camera API。

使用 MainActivity 上的按钮打开 CameraActivity 没有问题，但是如果我从 MainACtivity onCreate 方法打开 CameraActivity，那么我将面临以下错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.setDisplayOrientation(int)' on a null object reference
            at com.vivertechnologies.camera.ShowCamera.refreshCamera(ShowCamera.java:208)
            at com.vivertechnologies.camera.ShowCamera.surfaceChanged(ShowCamera.java:281)
            at android.view.SurfaceView.updateWindow(SurfaceView.java:590)
            at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:176)
            at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:847)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1983)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1081)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5818)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:550)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5234)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)

我的 Camera API 代码是:

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.camera_show);

        Thread t = new Thread() {

            @Override
            public void run() {
                try {
                    while (!isInterrupted()) {
                        Thread.sleep(1000);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                // update TextView here!
                                Calendar c = Calendar.getInstance();
                                SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
                                String formattedDate = df.format(c.getTime());
                                TextView txtView = (TextView)findViewById(R.id.dateTime);
                                txtView.setText(formattedDate);
                            }
                        });
                    }
                } catch (InterruptedException e) {
                }
            }
        };

        t.start();

        surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
        surfaceHolder = surfaceView.getHolder();

        surfaceHolder.addCallback(this);
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

        jpegCallback = new PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {
                new Thread(new SavePicThread(data)).start();
//
//                Intent i = new Intent(ShowCamera.this, UploadActivity.class);
//                i.putExtra("isImage", data);
//                startActivity(i);
                refreshCamera();
            }
        };
    }

刷新产生错误的相机方法:

public void refreshCamera() {
        if (surfaceHolder.getSurface() == null) {
            // preview surface does not exist
            return;
        }
        // stop preview before making changes
        try {
            camera.stopPreview();
        } catch (Exception e) {
            // ignore: tried to stop a non-existent preview
        }

        int rotation = ((WindowManager)ShowCamera.this.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getRotation();
        int degrees = 0;

        // specifically for back facing camera
        switch (rotation) {
            case Surface.ROTATION_0:
                degrees = 90;
                break;
            case Surface.ROTATION_90:
                degrees = 0;
                break;
            case Surface.ROTATION_180:
                degrees = 270;
                break;
            case Surface.ROTATION_270:
                degrees = 180;
                break;
        }


        camera.setDisplayOrientation(degrees);
        setCamera(camera);
        try {
            camera.setPreviewDisplay(surfaceHolder);
            camera.startPreview();
        } catch (Exception e) {
            Log.d("AAAAA", "Error starting camera preview: " + e.getMessage());
        }
    }

我无法确定如何解决它。

编辑:

完整代码:

    package com.vivertechnologies.camera;


import android.content.Context;
import android.content.Intent;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.Menu;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.WindowManager;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

/**
 * Created by usman on 27/11/15.
 */
public class ShowCamera extends MainActivity implements SurfaceHolder.Callback {
    Camera camera;
    SurfaceView surfaceView;
    SurfaceHolder surfaceHolder;

    Camera.PictureCallback rawCallback;
    Camera.ShutterCallback shutterCallback;
    Camera.PictureCallback jpegCallback;


    private Camera.Size mPreviewSize;
    private List<Camera.Size> mSupportedPreviewSizes;
    private Context mContext;
    private SurfaceView mSurfaceView;
    private SurfaceHolder mHolder;
    private final String TAG = "CameraSurfaceView";
    private Camera mCamera;
    private List<String> mSupportedFlashModes;

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

        Thread t = new Thread() {

            @Override
            public void run() {
                try {
                    while (!isInterrupted()) {
                        Thread.sleep(1000);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                // update TextView here!
                                Calendar c = Calendar.getInstance();
                                SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
                                String formattedDate = df.format(c.getTime());
                                TextView txtView = (TextView)findViewById(R.id.dateTime);
                                txtView.setText(formattedDate);
                            }
                        });
                    }
                } catch (InterruptedException e) {
                }
            }
        };

        t.start();

        surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
        surfaceHolder = surfaceView.getHolder();

        surfaceHolder.addCallback(this);
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

        jpegCallback = new PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {
                new Thread(new SavePicThread(data)).start();
//
//                Intent i = new Intent(ShowCamera.this, UploadActivity.class);
//                i.putExtra("isImage", data);
//                startActivity(i);
                refreshCamera();
            }
        };
    }

    private void galleryAddPic(File file) {
        Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        Uri contentUri = Uri.fromFile(file);
        mediaScanIntent.setData(contentUri);
        ShowCamera.this.sendBroadcast(mediaScanIntent);
    }


    public class SavePicThread implements Runnable {
        byte[] data;
        public SavePicThread(byte[] data) {
            this.data = data;
        }
        public void run() {
            // make a new picture file
            File pictureFile = getOutputMediaFile();

            if (pictureFile == null) {
                return;
            }
            try {
                // write to the file
                FileOutputStream fos = new FileOutputStream(pictureFile);
                fos.write(data);
                fos.flush();
                fos.close();
                ShowCamera.this.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
//                        Toast toast = Toast.makeText(ShowCamera.this, "Picture saved", Toast.LENGTH_SHORT);
//                        toast.show();
                    }
                });
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            // make the picture visible to the rest of the device
            galleryAddPic(pictureFile);
            Intent i = new Intent(ShowCamera.this, UploadActivity.class);
            i.putExtra("filePath", pictureFile.getPath());
            startActivity(i);
        }
    }

    // make picture and save to a folder
    private File getOutputMediaFile() {
        // make a new file directory inside the "sdcard" folder
        File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_PICTURES), "imgCaptureApp");

        // if the directory does not exist
        if (!mediaStorageDir.exists()) {
            // if you cannot make this directory return
            if (!mediaStorageDir.mkdirs()) {
                return null;
            }
        }

        // take the current timeStamp
        String timeStamp = new SimpleDateFormat("dd-MM-yyyy_HH:mm:ss").format(new Date());
        File mediaFile;
        // and make a media file:
        mediaFile = new File(mediaStorageDir.getPath() + File.separator + "IMG_" + timeStamp + ".jpg");

        return mediaFile;
    }



    public void captureImage(View v) throws IOException {
        camera.takePicture(null, null, jpegCallback);
    }

    public void refreshCamera() {
        if (surfaceHolder.getSurface() == null) {
            // preview surface does not exist
            return;
        }
        // stop preview before making changes
        try {
            camera.stopPreview();
        } catch (Exception e) {
            // ignore: tried to stop a non-existent preview
        }

        int rotation = ((WindowManager)ShowCamera.this.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getRotation();
        int degrees = 0;

        // specifically for back facing camera
        switch (rotation) {
            case Surface.ROTATION_0:
                degrees = 90;
                break;
            case Surface.ROTATION_90:
                degrees = 0;
                break;
            case Surface.ROTATION_180:
                degrees = 270;
                break;
            case Surface.ROTATION_270:
                degrees = 180;
                break;
        }


        camera.setDisplayOrientation(degrees);
        setCamera(camera);
        try {
            camera.setPreviewDisplay(surfaceHolder);
            camera.startPreview();
        } catch (Exception e) {
            Log.d("AAAAA", "Error starting camera preview: " + e.getMessage());
        }
    }

    public void setCamera(Camera camera)
    {
        Camera mCamera = camera;
        if (mCamera != null)
        {
            mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
            mSupportedFlashModes = mCamera.getParameters().getSupportedFlashModes();
            // Set the camera to Auto Flash mode.
            if (mSupportedFlashModes.contains(Camera.Parameters.FLASH_MODE_AUTO))
            {
                Camera.Parameters parameters = mCamera.getParameters();
                parameters.setFlashMode(Camera.Parameters.FLASH_MODE_AUTO);
                mCamera.setParameters(parameters);
            }
        }
        surfaceView.requestLayout();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            camera = Camera.open();
        }

        catch (RuntimeException e) {
            System.err.println(e);
            return;
        }

        Camera.Parameters param;
        param = camera.getParameters();

        List<Camera.Size> sizes = param.getSupportedPictureSizes();
        Camera.Size size = sizes.get(0);
        for(int i=0;i<sizes.size();i++)
        {
            if(sizes.get(i).width > size.width)
                size = sizes.get(i);
        }
        param.setPictureSize(size.width, size.height);
        param.setRotation(90);
        param.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
//        param.setPreviewSize(352, 288);
        camera.setParameters(param);

        try {
            camera.setPreviewDisplay(surfaceHolder);
            camera.startPreview();
        }

        catch (Exception e) {
            System.err.println(e);
            return;
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        refreshCamera();
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        camera.stopPreview();
        camera.release();
        camera = null;
    }
}

Answer 1

根据您的描述，您的问题似乎是 ShowCamera是 MainActivity 的子类.据推测，您在 MainActivity 中有类似于以下内容的内容的 onCreate()方法:

SharedPreferences prefs = ...

if(prefs.getBoolean("phone_number_set", false)) {
    startActivity(new Intent(this, ShowCamera.class));
}

自 ShowCamera是 MainActivity 的子类, 调用 super.onCreate(savedInstanceState);在ShowCamera的 onCreate()方法正在执行 MainActivity的 onCreate()再次方法。当你打开ShowCamera与 Button ，您还没有设置电话号码，所以 if上面显示的条件是 false , 和 startActivity()方法不会再次被调用。

但是，在设置电话号码后，条件为 true , 它开始 ShowCamera再次调用 MainActivity的 onCreate() , 它执行 if block ，开始 ShowCamera ，它调用 MainActivity的 onCreate() , 它执行 if block ，开始 ShowCamera ...这很容易通过添加 static int 来验证。到 ShowCamera类，将其打印到登录 onCreate() , 然后立即增加它。

最终，ShowCamera 之一实例将布局其 SurfaceView并调用refreshCamera()来自 surfaceChanged()回调，但它将有一个 null Camera对象，因为之前的 Activity 已经有 camera.open，它会抛出 NullPointerException你得到了。

解决方法很简单。更改 ShowCamera类是 Activity 的直接子类.即:

public class ShowCamera extends Activity implements SurfaceHolder.Callback {