4-2.Android Camera 之预览图像编码模板（SurfaceView）

一、Camera

1. Camera 用于捕获图像和视频

2. 在 Android 开发的早期阶段，Android 提供 android.hardware.Camera API，开发者用它来访问和控制设备的摄像头硬件

3. 然而，随着 Android 系统的发展，从 Android 5.0（API 级别 21）开始，Android 引入了一个新的 Camera2 API，以提供更强大和灵活的控制功能

---

二、Camera 预览图像

1、Util

• MyCameraTool.java

package com.my.camera.util;

import android.hardware.Camera;
import android.util.Log;

import com.my.camera.entity.CameraIdResult;

import java.util.List;

public class MyCameraTool {

    public static final String TAG = MyCameraTool.class.getSimpleName();

    /**
     * 得到摄像头 Id 对象
     *
     * @return 摄像头 Id 对象，它有前置摄像头 Id 和后置摄像头 Id
     */
    public static CameraIdResult getCameraIdResult() {
        CameraIdResult cameraIdResult = new CameraIdResult();

        int numberOfCameras = Camera.getNumberOfCameras();
        Log.i(TAG, "------------------------------ 摄像头个数：" + numberOfCameras);

        for (int cameraId = 0; cameraId < numberOfCameras; cameraId++) {
            Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
            Camera.getCameraInfo(cameraId, cameraInfo);
            if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
                Log.i(TAG, "------------------------------ 前置摄像头，cameraId 为：" + cameraId);
                cameraIdResult.setQzCameraId(cameraId);
            }
            if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_BACK) {
                Log.i(TAG, "------------------------------ 后置摄像头，cameraId 为：" + cameraId);
                cameraIdResult.setHzCameraId(cameraId);
            } else {
                Log.i(TAG, "------------------------------ 其他摄像头，cameraId 为：" + cameraId);
            }
        }

        return cameraIdResult;
    }

    /**
     * 根据 SurfaceView 的尺寸和相机支持的预览尺寸来选择最优的预览尺寸
     *
     * @param sizes 相机支持的预览尺寸列表
     * @param w     SurfaceView 的宽度
     * @param h     SurfaceView 的高度
     * @return 最优的预览尺寸，如果没有合适的尺寸则返回 null
     */
    public static Camera.Size getOptimalPreviewSize(List<Camera.Size> sizes, int w, int h) {
        if (sizes == null) return null;

        final double ASPECT_TOLERANCE = 0.1;
        double targetRatio = (double) h / w;
        Camera.Size optimalSize = null;
        double minDiff = Double.MAX_VALUE;
        int targetHeight = h;

        // 遍历所有支持的预览尺寸
        for (Camera.Size size : sizes) {

            // 检查宽高比是否接近目标宽高比
            double ratio = (double) size.width / size.height;
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;

            // 计算当前尺寸与目标尺寸的宽度差异
            // 如果差异小于当前最小差异，则更新最优尺寸和最小差异
            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        // 如果找不到接近目标宽高比的尺寸，则选择最接近目标高度的尺寸
        if (optimalSize == null) {
            minDiff = Double.MAX_VALUE;
            for (Camera.Size size : sizes) {
                if (Math.abs(size.height - targetHeight) < minDiff) {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }

        return optimalSize;
    }
}

• CameraIdResult.java

package com.my.camera.entity;

public class CameraIdResult {
    private int qzCameraId = -1; // 前置摄像头 id
    private int hzCameraId = -1; // 后置摄像头 id

    public CameraIdResult() {
    }

    public CameraIdResult(int qzCameraId, int hzCameraId) {
        this.qzCameraId = qzCameraId;
        this.hzCameraId = hzCameraId;
    }

    public int getQzCameraId() {
        return qzCameraId;
    }

    public void setQzCameraId(int qzCameraId) {
        this.qzCameraId = qzCameraId;
    }

    public int getHzCameraId() {
        return hzCameraId;
    }

    public void setHzCameraId(int hzCameraId) {
        this.hzCameraId = hzCameraId;
    }
}

2、Activity Layout

• activity_preview_image.xml

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".PreviewImageActivity">

    <SurfaceView
        android:id="@+id/sv"
        android:layout_width="300dp"
        android:layout_height="300dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
androidx.constraintlayout.widget.ConstraintLayout>

3、Activity Code

• PreviewImageActivity.java

package com.my.camera;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.hardware.Camera;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.WindowManager;

import com.my.camera.entity.CameraIdResult;
import com.my.camera.util.MyCameraTool;

import java.io.IOException;
import java.util.List;

public class PreviewImageActivity extends AppCompatActivity {

    public static final String TAG = PreviewImageActivity.class.getSimpleName();

    private SurfaceView sv;

    private SurfaceHolder surfaceHolder;
    private int hzCameraId;
    private Camera camera;

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

        // 保持屏幕常亮
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        CameraIdResult cameraIdResult = MyCameraTool.getCameraIdResult();
        hzCameraId = cameraIdResult.getHzCameraId();

        sv = findViewById(R.id.sv);

        surfaceHolder = sv.getHolder();
        surfaceHolder.addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(@NonNull SurfaceHolder holder) {
                Log.i(TAG, "------------------------------ surfaceCreated");
                openCamera();
            }

            @Override
            public void surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height) {
                Log.i(TAG, "------------------------------ surfaceChanged");
                cameraPreview(width, height);
            }

            @Override
            public void surfaceDestroyed(@NonNull SurfaceHolder holder) {
                Log.i(TAG, "------------------------------ surfaceDestroyed");
                closeCamera();
            }
        });
    }

    private void openCamera() {
        try {
            if (camera != null) return;
            if (hzCameraId == -1) return;
            camera = Camera.open(hzCameraId);
            camera.setPreviewDisplay(surfaceHolder);
            camera.setDisplayOrientation(90);
            camera.setPreviewCallback(new Camera.PreviewCallback() {
                @Override
                public void onPreviewFrame(byte[] data, Camera camera) {
                    Log.i(TAG, "------------------------------ 得到预览帧数据的 size 为 " + data.length);
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
            closeCamera();
        }
    }

    private void cameraPreview(int width, int height) {
        if (camera == null) return;
        Camera.Parameters parameters = camera.getParameters();
        List<Camera.Size> supportedPreviewSizes = parameters.getSupportedPreviewSizes();
        Camera.Size previewSize = MyCameraTool.getOptimalPreviewSize(supportedPreviewSizes, width, height);
        parameters.setPreviewSize(previewSize.width, previewSize.height);
        camera.setParameters(parameters);
        camera.startPreview();
    }

    private void closeCamera() {
        if (camera == null) return;
        camera.setPreviewCallback(null);
        camera.stopPreview();
        camera.release();
        camera = null;
    }
}

---

三、Camera 预览图像案例解析

1、添加权限

• 在 AndroidManifest.xml 文件中添加相关权限，如果是 Android 6.0（API 级别 23）或之后，需要在运行时请求

<uses-permission android:name="android.permission.CAMERA" />

2、保持屏幕常亮

• 保持屏幕常亮就是不会自动关闭屏幕，不仅是预览图像，它也非常适用于阅读、视频播放等

getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

3、选择摄像头

• 这里借助工具类，选择后置摄像头（手机背后的）

CameraIdResult cameraIdResult = MyCameraTool.getCameraIdResult();
hzCameraId = cameraIdResult.getHzCameraId();

4、准备 SurfaceView 作为预览图像容器

• SurfaceView 控件可用于预览图像、视频播放等

<SurfaceView
    android:id="@+id/sv"
    android:layout_width="300dp"
    android:layout_height="300dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

• 通过 SurfaceView 对象得到 SurfaceHolder 对象，它作为预览图像显示，它有三个方法

1. surfaceCreated(@NonNull SurfaceHolder holder)：当 Surface 被创建时调用，这里可以打开相机

2. surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height)：当 Surface 的尺寸或格式发生变化时调用，这里可以调整相机预览的尺寸

3. surfaceDestroyed(@NonNull SurfaceHolder holder)：当 Surface 被销毁时调用，这里可以关闭相机

sv = findViewById(R.id.sv);

surfaceHolder = sv.getHolder();
surfaceHolder.addCallback(new SurfaceHolder.Callback() {
    @Override
    public void surfaceCreated(@NonNull SurfaceHolder holder) {
        Log.i(TAG, "------------------------------ surfaceCreated");
        openCamera();
    }

    @Override
    public void surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height) {
        Log.i(TAG, "------------------------------ surfaceChanged");
        cameraPreview(width, height);
    }

    @Override
    public void surfaceDestroyed(@NonNull SurfaceHolder holder) {
        Log.i(TAG, "------------------------------ surfaceDestroyed");
        closeCamera();
    }
});

5、打开相机

1. camera = Camera.open(hzCameraId);：通过打开摄像头

2. camera.setPreviewDisplay(surfaceHolder);：设置预览图像显示

3. camera.setDisplayOrientation(90);：设置预览方向（否则图像不是正向的）

4. camera.setPreviewCallback(......：注册一个预览回调来接收预览帧数据

private void openCamera() {
    try {
        if (camera != null) return;
        if (hzCameraId == -1) return;
        camera = Camera.open(hzCameraId);
        camera.setPreviewDisplay(surfaceHolder);
        camera.setDisplayOrientation(90);
        camera.setPreviewCallback(new Camera.PreviewCallback() {
            @Override
            public void onPreviewFrame(byte[] data, Camera camera) {
                Log.i(TAG, "------------------------------ 得到预览帧数据的 size 为 " + data.length);
            }
        });
    } catch (IOException e) {
        e.printStackTrace();
        closeCamera();
    }
}

6、调整相机预览的尺寸

1. Camera.Parameters parameters = camera.getParameters();：得到相机参数对象

2. List supportedPreviewSizes = parameters.getSupportedPreviewSizes();：得到支持的预览尺寸列表

3. camera.setParameters(parameters);：借助工具类选择最优的预览尺寸并设置

4. camera.startPreview();：开始预览图像

private void cameraPreview(int width, int height) {
    if (camera == null) return;
    Camera.Parameters parameters = camera.getParameters();
    List<Camera.Size> supportedPreviewSizes = parameters.getSupportedPreviewSizes();
    Camera.Size previewSize = MyCameraTool.getOptimalPreviewSize(supportedPreviewSizes, width, height);
    parameters.setPreviewSize(previewSize.width, previewSize.height);
    camera.setParameters(parameters);
    camera.startPreview();
}

7、关闭相机

1. camera.setPreviewCallback(null);：移除预览回调

2. camera.stopPreview();：停止预览图像

3. camera.release();：释放摄像头资源

private void closeCamera() {
    if (camera == null) return;
    camera.setPreviewCallback(null);
    camera.stopPreview();
    camera.release();
    camera = null;
}