在android中，通过相机获取预览界面的需求似乎很变态，好像也没有什么使用场景。但是，有一个场景需要获取预览界面的图像，就是扫码，比如微信，支付宝的扫一扫，就是需要获取预览界面的图像数据的。
实现逻辑比较简单，不过肯定比打开系统相机要麻烦一点的。
下面简单说一下实现步骤：
实例化一个SurfaceView。在surfaceCreated()回调中去实例化Camera对象，去自动对焦。在onAutoFocus()回调中去调用camera.takePicture(null,null,callback);。在第3步的callback里面去获取预览图像数据int data[]。（可选）将获取的数据换成成文件。（可选）将该文件对象加载成bitmap对象。在不使用的使用释放相机资源。
代码细节：
清单文件：
<uses-feature android:name="android.hardware.camera" /><uses-feature android:name="android.hardware.camera.autofocus" /><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /><uses-permission android:name="android.permission.CAMERA" /><uses-permission android:name="android.permission.RECORD_AUDIO" />
java代码：
package com.python.cat.testgradle;import android.Manifest;import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.hardware.Camera;import android.os.Bundle;import android.view.SurfaceHolder;import android.view.SurfaceView;import android.view.View;import android.widget.Button;import android.widget.FrameLayout;import android.widget.Toast;import com.apkfuns.logutils.LogUtils;import com.google.zxing.BinaryBitmap;import com.google.zxing.ChecksumException;import com.google.zxing.FormatException;import com.google.zxing.NotFoundException;import com.google.zxing.RGBLuminanceSource;import com.google.zxing.Result;import com.mon.GlobalHistogramBinarizer;import com.google.zxing.qrcode.QRCodeReader;import com.yanzhenjie.permission.Action;import com.yanzhenjie.permission.AndPermission;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.util.Arrays;import java.util.List;public class UseCameraActivity extends Activity {private Activity get() {return this;}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_asome);setTitle(getClass().getSimpleName());final FrameLayout frameLayout = findViewById(R.id.prev_content_layout);Button btn = findViewById(R.id.start_camera_preview);btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {AndPermission.with(get()).permission(Manifest.permission.CAMERA,Manifest.permission.WRITE_EXTERNAL_STORAGE).onDenied(new Action() {@Overridepublic void onAction(List<String> permissions) {LogUtils.e("error....." + permissions);}}).onGranted(new Action() {@Overridepublic void onAction(List<String> permissions) {LogUtils.w("you can do..");ScanView scanView = new ScanView(get());frameLayout.removeAllViews();frameLayout.addView(scanView);}}).start();}});}static class ScanView extends SurfaceView implements SurfaceHolder.Callback,Camera.AutoFocusCallback {private Camera mCamera;private final File fileImg;private ScanView self;public ScanView(Context context) {super(context);fileImg = new File(context.getCacheDir(), "prev_view.jpg");SurfaceHolder mHolder = getHolder();self = this;mHolder.addCallback(this);// deprecated setting, but required on Android versions prior to 3.0mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);}@Overridepublic void onAutoFocus(boolean success, Camera camera) {LogUtils.w("auto focus..." + success);if (mCamera != null) {mCamera.takePicture(null, null, null, new Camera.PictureCallback() {@Overridepublic void onPictureTaken(byte[] data, Camera camera) {mCamera.cancelAutoFocus();mCamera.stopPreview(); // 拿到数据就停止！！！LogUtils.w("========data========");LogUtils.w("----------data-----------------");// camera.startPreview();File pictureFile = fileImg;if (pictureFile == null) {LogUtils.e("Error creating media file, check storage permissions: " +null);return;}if (data == null) {return;}try {LogUtils.d(data);FileOutputStream fos = new FileOutputStream(pictureFile);fos.write(data);fos.close();LogUtils.e("save preview complete###!!!");LogUtils.e("save preview complete###!!!" + pictureFile);BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeFile(pictureFile.getAbsolutePath(), options);options.inJustDecodeBounds = false;int outWidth = options.outWidth;int outHeight = options.outHeight;if (outWidth >= getWidth() * 2) {options.inSampleSize = outWidth / getWidth();}if (outHeight >= getHeight() * 2) {options.inSampleSize = outHeight / getHeight();}Bitmap bmp = BitmapFactory.decodeFile(pictureFile.getAbsolutePath(), options);Result result = parseInfoFromBitmap(bmp);if (result != null) {Toast.makeText(getContext(), "INFO:" + result.getText(), Toast.LENGTH_SHORT).show();LogUtils.w("解析成功：" + result);} else {LogUtils.e("再次尝试中....");mCamera.startPreview();mCamera.autoFocus(self);// todo:这里也可以做最大重试次数的限制...}} catch (Exception e) {LogUtils.e("Error accessing file: " + e.getMessage());}}});}}public Result parseInfoFromBitmap(Bitmap bitmap) {int[] pixels = new int[bitmap.getWidth() * bitmap.getHeight()];bitmap.getPixels(pixels, 0, bitmap.getWidth(), 0, 0, bitmap.getWidth(), bitmap.getHeight());LogUtils.w("### pixels dest==" + Arrays.toString(pixels));RGBLuminanceSource source = new RGBLuminanceSource(bitmap.getWidth(),bitmap.getHeight(), pixels);GlobalHistogramBinarizer binarizer = new GlobalHistogramBinarizer(source);BinaryBitmap image = new BinaryBitmap(binarizer);Result result = null;try {result = new QRCodeReader().decode(image);return result;} catch (NotFoundException e) {e.printStackTrace();Toast.makeText(getContext(), "非二维码图片，不能解析", Toast.LENGTH_SHORT).show();} catch (ChecksumException e) {e.printStackTrace();} catch (FormatException e) {e.printStackTrace();}return null;}@Overridepublic void surfaceCreated(SurfaceHolder holder) {LogUtils.e("x surfaceCreated.. #####");try {mCamera = Camera.open();mCamera.setPreviewDisplay(holder);mCamera.setDisplayOrientation(90);Camera.Parameters parameters = mCamera.getParameters();//parameters.setPictureSize(1600, 1200);//parameters.setPreviewSize(640, 480);mCamera.setParameters(parameters);mCamera.startPreview();mCamera.autoFocus(this);LogUtils.e("surfaceCreated.. #####");} catch (IOException e) {LogUtils.e("Error setting camera preview: " + e.getMessage());}}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {LogUtils.w("--change-");}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {LogUtils.w("destroy--");if (mCamera != null) {mCamera.cancelAutoFocus();mCamera.stopPreview();mCamera.release();}}}}
布局文件：
<RelativeLayout xmlns:android="/apk/res/android"xmlns:app="/apk/res-auto"xmlns:tools="/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".UseCameraActivity"><Button android:id="@+id/start_camera_preview"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:text="@string/start_camera_preview" /><FrameLayout android:id="@+id/prev_content_layout"android:layout_width="match_parent"android:layout_height="match_parent"android:layout_above="@id/start_camera_preview"></FrameLayout></RelativeLayout>
gradle配置（可选）：
implementation 'com.yanzhenjie:permission:2.0.0-rc4' // 运行时权限语法糖implementation 'com.google.zxing:core:3.3.1' // zxing 解析二维码图片
嗯，以上就是获取相机预览图像数据的代码了。不过，这里用的Camera接口是过时的了，不建议使用。不过可以运行。我目前的compileSdkVersion=26。
就酱咯。 完整app代码也许有的吧。
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update: 关于Camera2，我选择放弃….
官方的说法是：
The android.hardware.camera2 package provides an interface to individual camera devices connected to an Android device. It replaces the deprecated Camera class.
This package models a camera device as a pipeline, which takes in input requests for capturing a single frame, captures the single image per the request, and then outputs one capture result metadata packet, plus a set of output image buffers for the request. The requests are processed in-order, and multiple requests can be in flight at once. Since the camera device is a pipeline with multiple stages, having multiple requests in flight is required to maintain full framerate on most Android devices.
反正是看懂了一句话，就是用来替代Camera的。
但是，真的很麻烦。我没有找到中文的，可以直接运行的案例，找到了两个外国人写的博客，里面给了完整的代码。不过估计不能直接访问。我把拷贝到我的项目里面去了。可以直接运行。
完整app代码
因为每一篇代码都很长，我就不贴出来了，说一下路径。
com.python.cat.testgradle.MainActivity.java[由于这个原始代码没有加动态权限申请，我手动添加了一下…]
com.python.cat.testgradle.AndroidCameraApi.java
我给的是我代码的路径，以及原始链接。
不清楚是出于什么考虑，camera2里面比camera多了好几类，复杂度也提升了不少。有需要的可以研究一下。上手难度大于camera。（目前我还是一头雾水，对于camera2）。
中文的找到一个：这个我并没有去下载运行验证，不过看博客里面写的挺多的。
