Android Camera2 拍照（三）——切换摄像头，延时拍摄和闪光模式

原文:Android Camera2 拍照（三）——切换摄像头，延时拍摄和闪光模式

一、切换摄像头

在前后摄像头之间切换，首先需要关闭之前打开的摄像头，关闭preview，之后重新打开新的摄像头，重新打开preview。

public void switchCamera() {
        if (mCameraId.equals(CAMERA_FRONT)) {
            mCameraId = CAMERA_BACK;
            closeCamera();
            reopenCamera();

        } else if (mCameraId.equals(CAMERA_BACK)) {
            mCameraId = CAMERA_FRONT;
            closeCamera();
            reopenCamera();
        }
    }

关闭摄像头：

/**
     * Closes the current {@link CameraDevice}.
     */
    private void closeCamera() {
        try {
            mCameraOpenCloseLock.acquire();
            synchronized (mCameraStateLock) {

                // Reset state and clean up resources used by the camera.
                // Note: After calling this, the ImageReaders will be closed after any background
                // tasks saving Images from these readers have been completed.
                mPendingUserCaptures = 0;
                mState = STATE_CLOSED;
                if (null != mCaptureSession) {
                    mCaptureSession.close();
                    mCaptureSession = null;
                }
                if (null != mCameraDevice) {
                    mCameraDevice.close();
                    mCameraDevice = null;
                }
                if (null != mJpegImageReader) {
                    mJpegImageReader.close();
                    mJpegImageReader = null;
                }
                if (null != mRawImageReader) {
                    mRawImageReader.close();
                    mRawImageReader = null;
                }
            }
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted while trying to lock camera closing.", e);
        } finally {
            mCameraOpenCloseLock.release();
        }
    }

打开新的摄像头：

public void reopenCamera() {
        if (mTextureView.isAvailable()) {
            openCamera();
        } else {
            mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
        }
    }

如果TextureView是available的，那么直接调用openCamera（）打开camera（openCamera()的代码参考之前的博客）；如果|TextureView是unavailable的，那么调用TextureView的setSurfaceTextureListener设置SurfaceTextureListener（参考上一篇博客）。

二、延时拍摄

要实现延时拍摄，核心是实现一个定时器。本例延时分为三种模式：3s延时，10s按时，无延时。可以在三种模式之中自有切换。

private void switchDelayState() {
        switch (mDelayState) {
            case 0:
                mTimer.setImageResource(R.mipmap.ic_3s);
                mDelayTime = 3 * 1000;
                mDelayState = 1;
                break;
            case 1:
                mTimer.setImageResource(R.mipmap.ic_10s);
                mDelayTime = 10 * 1000;
                mDelayState = 2;
                break;
            case 2:
                mTimer.setImageResource(R.mipmap.timer);
                mDelayTime = 0;
                mDelayState = 0;
                break;
            default:
                break;
        }
    }

变量mDelayTime和mDelaySate的定义：

/*
     * Delay state, 0 represents no delay, 1 represents 3s delay, while 2 represents 10s delay
     */
    private short mDelayState = 0; // Timer
    private short mDelayTime;

当拍摄按钮被点击时：

@Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.capture: {
                if (mDelayState == 0) {
                    takePicture();
                } else {
                    new CountDownTimer(mDelayTime, TIME_INTERVAL) {
                        @Override
                        public void onTick(long millisUntilFinished) {
                            mTimeText.setVisibility(View.VISIBLE);
                            mTimeText.setText("" + millisUntilFinished / TIME_INTERVAL);
                        }

                        @Override
                        public void onFinish() {
                            mTimeText.setVisibility(View.GONE);
                            takePicture();
                        }
                    }.start();
                }
                break;
            }

但有3s或10s延时的时候，利用CountDownTimer实现倒计时并每隔一秒更新剩余时间提示，到时候执行拍照功能。

三、切换闪光模式

支持自动，强制，禁止闪光。与闪光模式有关的属性是CaptureRequest.CONTROL_AE_MODE和CaptureRequest.FLASH_MODE。 如果要使用FLASH_MODE属相，闪光灯必须可用，并且，CONTROL_AE_MODE必须设置为on或off，否则，自动曝光属性的ON_AUTO_FLASH,ON_ALWAYS_FLASH,
ON_AUTO_FLASH_REDEYE将会覆盖FLASH_MODE的设置。

private void switchFlashMode() {
        switch (mFlashMode) {
            case 0:
                mFlashMode = 1;
                mFlashBtn.setImageResource(R.mipmap.flash_auto);
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                try {
                    mCaptureSession.setRepeatingRequest(
                            mPreviewRequestBuilder.build(),
                            mPreCaptureCallback, mBackgroundHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                    return;
                }

                break;
            case 1:
                mFlashMode = 2;
                mFlashBtn.setImageResource(R.mipmap.flash_on);
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
                try {
                    mCaptureSession.setRepeatingRequest(
                            mPreviewRequestBuilder.build(),
                            mPreCaptureCallback, mBackgroundHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                    return;
                }
                break;
            case 2:
                mFlashMode = 0;
                mFlashBtn.setImageResource(R.mipmap.flash_off);
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);
                mPreviewRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
                try {
                    mCaptureSession.setRepeatingRequest(
                            mPreviewRequestBuilder.build(),
                            mPreCaptureCallback, mBackgroundHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                    return;
                }
                break;
        }
    }

在takePicture（）之前，需要再次设置：

private void setFlashMode() {
        switch (mFlashMode) {
            case 0:
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);
                mPreviewRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
                break;
            case 1:
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                break;
            case 2:
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
                break;
        }
    }

代码参考：https://github.com/gengqifu/361Camera，欢迎fork/star。