通过 Camera API 2 捕获图片并将其保存为位图

Question

我正在开发一个使用相机拍照然后在另一个活动中显示的应用程序，我尝试了以下代码

public void onImageAvailable(ImageReader imageReader) {
        Image image = imageReader.acquireLatestImage();
        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
        byte[] bytes = new byte[buffer.remaining()];
        buffer.get(bytes);
        Bitmap myBitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length, null);
        SetBitmap setBitmap = new SetBitmap();
        setBitmap.setMbitmap(myBitmap);
        image.close();
    }

在此之后，我在像这样的其他活动中获得我的位图

    myBitmap = CamActivity.setBitmap.getMbitmap();
    ImageView myImage = (ImageView) findViewById(R.id.imageView);
    myImage.setImageBitmap(myBitmap);

SetBitmap 是一个设置位图的类

当我点击它时，我有一个捕捉摄像头的按钮，它假设拍照并启动另一个活动来显示图像，但它随后崩溃 那么我现在该怎么办我以错误的方式开始我的活动？或者问题出在位图上？ 这是错误日志

                                                                         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.camtest/com.example.android.camtest.DisplayActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.Bitmap com.example.android.camtest.SetBitmap.getMbitmap()' on a null object reference
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
                                                                             at android.app.ActivityThread.access$900(ActivityThread.java:177)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:145)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5942)
                                                                             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:1400)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
                                                                          Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.Bitmap com.example.android.camtest.SetBitmap.getMbitmap()' on a null object reference
                                                                             at com.example.android.camtest.DisplayActivity.onCreate(DisplayActivity.java:37)
                                                                             at android.app.Activity.performCreate(Activity.java:6283)
                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758) 
                                                                             at android.app.ActivityThread.access$900(ActivityThread.java:177) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                             at android.os.Looper.loop(Looper.java:145) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5942) 
                                                                             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:1400) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195) 

                                                                       java.lang.IllegalStateException: Handler (android.media.ImageReader$ListenerHandler) {b9cb033} sending message to a Handler on a dead thread
                                                                           at android.os.MessageQueue.enqueueMessage(MessageQueue.java:325)
                                                                           at android.os.Handler.enqueueMessage(Handler.java:631)
                                                                           at android.os.Handler.sendMessageAtTime(Handler.java:600)
                                                                           at android.os.Handler.sendMessageDelayed(Handler.java:570)
                                                                           at android.os.Handler.sendEmptyMessageDelayed(Handler.java:534)
                                                                           at android.os.Handler.sendEmptyMessage(Handler.java:519)
                                                                           at android.media.ImageReader.postEventFromNative(ImageReader.java:511)
                                                                           at android.hardware.camera2.legacy.LegacyCameraDevice.nativeProduceFrame(Native Method)
                                                                           at android.hardware.camera2.legacy.LegacyCameraDevice.produceFrame(LegacyCameraDevice.java:516)
                                                                           at android.hardware.camera2.legacy.RequestThreadManager$2.onPictureTaken(RequestThreadManager.java:224)
                                                                           at android.hardware.Camera$EventHandler.handleMessage(Camera.java:1142)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:145)
                                                                           at android.hardware.camera2.legacy.CameraDeviceUserShim$CameraLooper.run(CameraDeviceUserShim.java:144)
                                                                           at java.lang.Thread.run(Thread.java:818)

这是我拍照的地方

private void takePic() {
    if (cameraDevice == null)
        return;
    CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraDevice.getId());
        Size[] jpegSizes = null;
        if (characteristics != null)
            jpegSizes = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
                    .getOutputSizes(ImageFormat.JPEG);

        int width = 700;
        int height = 600;

        if (jpegSizes != null && jpegSizes.length > 0) {
            width = jpegSizes[0].getWidth();
            height = jpegSizes[0].getHeight();
        }
        final ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
        List<Surface> outputSurface = new ArrayList<>(2);
        outputSurface.add(reader.getSurface());
        outputSurface.add(new Surface(textureView.getSurfaceTexture()));

        final CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
        captureBuilder.addTarget(reader.getSurface());
        captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);

        int rotation = getWindowManager().getDefaultDisplay().getRotation();
        captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));


        String fileName = "IMG_" + new SimpleDateFormat("yyyyMMdd-HHmmss").format(new Date()) + ".jpg";

        File captureDirectory = new File("/Download");

        if (!captureDirectory.isDirectory()) captureDirectory.mkdirs();
        final File mediaFile = new File(captureDirectory, fileName);

        final Uri fileUri = FileProvider.getUriForFile(this,
                "com.mydomain.fileprovider",
                mediaFile);


        ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader imageReader) {

                Image mImage = imageReader.acquireLatestImage();
                ByteBuffer buffer = mImage.getPlanes()[0].getBuffer();
                byte[] bytes = new byte[buffer.remaining()];
                buffer.get(bytes);
                try {
                    save(bytes);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                OutputStream output = null;
                try {
                    output = getContentResolver().openOutputStream(fileUri);
                    output.write(bytes);
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    mImage.close();
                    if (output != null) {
                        try {
                            output.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }


            }

            private void save(byte[] bytes) throws IOException {
                OutputStream output = null;
                try {
                    output = new FileOutputStream(mediaFile);
                    output.write(bytes);
                } finally {
                    if (output != null)
                        output.close();
                }

            }
        };
        Intent displayIntent = new Intent(this, DisplayActivity.class);
        displayIntent.putExtra("FILE_URI", fileUri);

        Log.e("uri", fileUri + "");


        startActivity(displayIntent);

        reader.setOnImageAvailableListener(readerListener, mBackgroundHandler);

        final CameraCaptureSession.CaptureCallback captureListener = new CameraCaptureSession.CaptureCallback() {
            @Override
            public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
                super.onCaptureCompleted(session, request, result);
                Toast.makeText(CamActivity.this, "Saved ", Toast.LENGTH_SHORT).show();

            }
        };


    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

这是显示活动

   @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display);
    imageView = findViewById(R.id.imageView);

    bundleExtras = getIntent().getExtras();
    if(bundleExtras != null){
        Uri savedBitmapUri = bundleExtras.getParcelable("FILE_URI");
        imageView.setImageURI(savedBitmapUri);
        Log.e("uri",savedBitmapUri+"");
    } else {
        Toast.makeText(this, "null pic", Toast.LENGTH_SHORT).show();

    }

}

文件提供者

<paths xmlns:android="http://schemas.android.com/apk/res/android">
<external-path name="myDownloads" path="Download" />
<root-path name="sdcard1" path="." /> </paths>

Answer 1

您将位图数据传递给另一个活动的方法是错误的。首先，您应该检查Android Activity Lifecycle。当你启动不同的 Activity 时，我们从 A 调用它 B，A Activity 将被销毁，所有资源都将被销毁。在 Android Activity LifeCycle 文档中，他们提到了这一点：

onDestroy() 回调释放所有尚未被释放的资源 由更早的回调（例如 onStop()）释放。

因此，活动销毁后您无法访问变量。您应该做的是，您应该将位图保存到文件中，并通过 Intent extra 传递文件 URI，并从另一个活动的 onCreate 回调中获取 URI。

您可以使用 FileProvider 来保存文件，并通过 Intent 传递提供者 URI，这是最好的“Android kind”方法，或者您可以保存文件的路径共享偏好，并从另一个不稳定且不是最佳实践的活动中读取它。

让我们使用 FileProvider： 您可以检查Android Documentation about FileProvider 来定义它。

// Assume that you added Captures path to your FileProvider's paths.
// Create temporary image file.
String fileName = "IMG_" + new SimpleDateFormat("yyyyMMdd-HHmmss").format(new Date()) + ".jpg";  
File captureDirectory = new File(getFilesDir(), "Captures");
if( !captureDirectory.isDirectory() ) captureDirectory.mkdirs();
File mediaFile = new File(captureDirectory, fileName);

Uri fileUri = FileProvider.getUriForFile(this,
                    "com.mydomain.fileprovider",
                    mediaFile);  

// Save the Bitmap.
public void onImageAvailable(ImageReader imageReader) {
    Image mImage = imageReader.acquireLatestImage();
    ByteBuffer buffer = mImage.getPlanes()[0].getBuffer();
    byte[] bytes = new byte[buffer.remaining()];
    buffer.get(bytes);
    OutputStream output = null;
    try {
        output = getContentResolver().openOutputStream(fileUri);
        output.write(bytes);
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        mImage.close();
        if (output != null) {
            try {
                output.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

// Pass the file uri via intent.
Intent displayIntent = new Intent(this, DisplayActivity.class);
displayIntent.putExtra("FILE_URI", mediaFile);
startActivity(displayIntent);

// Read the uri from started activity and show the bitmap
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display);

    ... 
    bundleExtras = getIntent().getExtras();
    if(bundleExtras != null){
        Uri savedBitmapUri = bundleExtras.getParcelable("FILE_URI");
        mImageView_Preview.setImageURI(savedBitmapUri);
    }
    else{
        // Uri not inside the intent data.
    }
    ...
}

您不应将所有字节作为位图加载到内存中。您只需将捕获的图像保存到文件中，然后传递从应用程序的 FileProvider 创建的文件 Uri，并使用一行代码显示文件 Uri。

基本优化： - 您可以在缓存目录中创建文件
- 完成任务后，您可以使用FileProvider permissions 删除文件。 - 您可以像 Google 在android-Camera2Basic 示例中所做的那样在后台线程上进行保存工作。 - 还有更多...