Android Camera使用指南

要自己写一个相机应用直接使用相机硬件，首先应用需要一个权限设置，在AndroidManifest.xml中加上使用设备相机的权限：

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

为你的应用创建自定义的相机，一般步骤如下：

　　1.检测相机硬件并获取访问

　　2.建立一个Preview类：需要一个相机预览的类，继承 SurfaceView 类，并实现SurfaceHolder接口。

　　3.建立预览的布局。

　　4.为拍照建立监听。

　　5.拍照并且存储文件。

　　6.释放相机。

　　因为相机是一个共享资源，所以应该被谨慎管理，这样应用之间才不会发生冲突。

　　所以使用完相机之后应该调用 Camera.release()来释放相机对象。

　　如果不释放，后续的使用相机请求（其他应用或本应用）都会失败。

检测相机硬件

如果你的程序没有在manifest的声明中要求有相机，那么你应该在运行时检查相机的存在与否，主要用了 PackageManager.hasSystemFeature() 方法。比如：

/** Check if this device has a camera */    private boolean checkCameraHardware(Context context)    {        if (context.getPackageManager().hasSystemFeature(                PackageManager.FEATURE_CAMERA))        {            // this device has a camera            return true;        }        else        {            // no camera on this device            return false;        }    }

设备上可能有多个相机，Android 2.3以后可以使用 Camera.getNumberOfCameras()来查看相机的数目。

　　如下面这段程序用于检测设备中的相机，并得到默认相机的索引号：

    private int getDefaultCameraId()    {        int defaultId = -1;        // Find the total number of cameras available        mNumberOfCameras = Camera.getNumberOfCameras();        // Find the ID of the default camera        CameraInfo cameraInfo = new CameraInfo();        for (int i = 0; i < mNumberOfCameras; i++)        {            Camera.getCameraInfo(i, cameraInfo);            if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK)            {                defaultId = i;            }        }        if (-1 == defaultId)        {            if (mNumberOfCameras > 0)            {                // 如果没有后向摄像头                defaultId = 0;            }            else            {                // 没有摄像头                Toast.makeText(getApplicationContext(), R.string.no_camera,                        Toast.LENGTH_LONG).show();            }        }        return defaultId;    }

看了Camera类的代码实现后，其中不带参数的open()方法：默认是调用后置摄像头

    public static Camera open()    {        int numberOfCameras = getNumberOfCameras();        CameraInfo cameraInfo = new CameraInfo();        for (int i = 0; i < numberOfCameras; i++)        {            getCameraInfo(i, cameraInfo);            if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK)            {                return new Camera(i);            }        }        return null;    }

访问相机

当检测到设备上有相机之后，必须获取其访问权，获取一个 Camera 类的对象。

　　要获取主要的相机，可以使用 Camera.open() 方法，注意异常处理。

　　在使用这个方法的时候一定要检查异常，如果相机正在被使用或者不存在，没有处理异常，将会使得应用被系统关闭。

　　如：

/** A safe way to get an instance of the Camera object. */    public static Camera getCameraInstance()    {        Camera c = null;        try        {            c = Camera.open(); // attempt to get a Camera instance        }        catch (Exception e)        {            // Camera is not available (in use or does not exist)        }        return c; // returns null if camera is unavailable    }

Android 2.3之后，可以使用Camera.open(int)来获取特定的相机。

检查相机特性

可以使用Camera.getParameters()方法来检查相机的特性。

　　API Level 9之后，可以使用 Camera.getCameraInfo()来查看相机是在设备前面还是后面，还可以得到图像的方向。

建立Preview类

　　为了有效地拍照或录像，用户必须要看到相机能看到的图像。

　　相机的preview类是一个 SurfaceView ，展示了相机正在捕捉的图像。

　　下面是一个预览类的例子（来自官网）：

/** A basic Camera preview class */public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {    private SurfaceHolder mHolder;    private Camera mCamera;    public CameraPreview(Context context, Camera camera) {        super(context);        mCamera = camera;        // Install a SurfaceHolder.Callback so we get notified when the        // underlying surface is created and destroyed.        mHolder = getHolder();        mHolder.addCallback(this);        // deprecated setting, but required on Android versions prior to 3.0        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);    }    public void surfaceCreated(SurfaceHolder holder) {        // The Surface has been created, now tell the camera where to draw the preview.        try {            mCamera.setPreviewDisplay(holder);            mCamera.startPreview();        } catch (IOException e) {            Log.d(TAG, "Error setting camera preview: " + e.getMessage());        }    }    public void surfaceDestroyed(SurfaceHolder holder) {        // empty. Take care of releasing the Camera preview in your activity.    }    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {        // If your preview can change or rotate, take care of those events here.        // Make sure to stop the preview before resizing or reformatting it.        if (mHolder.getSurface() == null){          // preview surface does not exist          return;        }        // stop preview before making changes        try {            mCamera.stopPreview();        } catch (Exception e){          // ignore: tried to stop a non-existent preview        }        // set preview size and make any resize, rotate or        // reformatting changes here        // start preview with new settings        try {            mCamera.setPreviewDisplay(mHolder);            mCamera.startPreview();        } catch (Exception e){            Log.d(TAG, "Error starting camera preview: " + e.getMessage());        }    }}

注意要设置尺寸的话需要放在surfaceChanged()方法里，调用 setPreviewSize()方法，并且应该使用 getSupportedPreviewSizes()返回的值，而不要使用任意的尺寸。

 

把Preview放在布局里面

　　布局时可以使用FrameLayout，这样其他的按钮或者元素可以叠加在预览图像上。

　　对于大多数设备来说，相机预览的默认方向是横放的（landscape）。

　　从Android 2.2 (API Level 8)开始，可以使用 setDisplayOrientation()来设置预览图像的方向。

　　如果需要在用户改变设备方向的时候改变预览图像的方向，可以在 surfaceChanged()方法中，首先用 Camera.stopPreview() 停止预览，改变方向，然后用Camera.startPreview()开启新的预览。

　　当然你也可以直接在manifest中设置好方向，如下：

<activity android:name=".CameraActivity"          android:label="@string/app_name"          android:screenOrientation="landscape">          <!-- configure this activity to use landscape orientation -->          <intent-filter>        <action android:name="android.intent.action.MAIN" />        <category android:name="android.intent.category.LAUNCHER" />    </intent-filter></activity>

拍照

　　在应用里面，必须为用户控制加上监听，来响应用户拍照的动作。

　　为了得到图像，要使用 Camera.takePicture()方法。

　　这个方法接收三个参数，用于从相机获取图像。

　　为了接收到JPEG格式的数据，需要实现Camera.PictureCallback接口用来接收图像数据并且写入文件。

　　下面的代码展示了一个最基本的实现：

private PictureCallback mPicture = new PictureCallback() {    @Override    public void onPictureTaken(byte[] data, Camera camera) {        File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);        if (pictureFile == null){            Log.d(TAG, "Error creating media file, check storage permissions: " +                e.getMessage());            return;        }        try {            FileOutputStream fos = new FileOutputStream(pictureFile);            fos.write(data);            fos.close();        } catch (FileNotFoundException e) {            Log.d(TAG, "File not found: " + e.getMessage());        } catch (IOException e) {            Log.d(TAG, "Error accessing file: " + e.getMessage());        }    }};

照相动作可以用按钮控制，如下：

// Add a listener to the Capture buttonButton captureButton = (Button) findViewById(id.button_capture);captureButton.setOnClickListener(    new View.OnClickListener() {        @Override        public void onClick(View v) {            // get an image from the camera            mCamera.takePicture(null, null, mPicture);        }    });

释放相机

　　相机是设备资源，被所有应用共享，当应用不使用相机时应当及时释放，应当在Activity.onPause()中释放。

　　如果不及时释放，后续的相机请求（包括你自己的应用和其他的应用发出的）都将失败并且导致应用退出。

 

 

实验程序

　　完整的照相程序需要考虑相机切换、预览图像的尺寸设置、焦距变换、缩放、白平衡的相机参数设置。

　　请查阅文后的参考资料进行进一步学习。

　　附上一个粗糙待完善的自定义相机程序（2013/4/6）

　　预览图像类：　

package com.example.hellocustomcamera;import java.io.IOException;import java.util.List;import android.R.integer;import android.content.Context;import android.graphics.ImageFormat;import android.graphics.PixelFormat;import android.hardware.Camera;import android.hardware.Camera.CameraInfo;import android.hardware.Camera.Size;import android.util.AttributeSet;import android.util.Log;import android.view.SurfaceHolder;import android.view.SurfaceView;/** * 相机图片预览类 *  * @author *  */public class CameraPreview extends SurfaceView implements        SurfaceHolder.Callback{    private SurfaceHolder mHolder;    private Camera mCamera;    Size mPreviewSize;    List<Size> mSupportedPreviewSizes;    public CameraPreview(Context context, AttributeSet attrs, int defStyle)    {        super(context, attrs, defStyle);        init();    }    public CameraPreview(Context context, AttributeSet attrs)    {        super(context, attrs);        init();    }    public CameraPreview(Context context)    {        super(context);        init();    }    /**     * 初始化工作     *      */    private void init()    {        Log.d(AppConstants.LOG_TAG, "CameraPreview initialize");        // Install a SurfaceHolder.Callback so we get notified when the        // underlying surface is created and destroyed.        mHolder = getHolder();        mHolder.addCallback(this);        // deprecated setting, but required on Android versions prior to 3.0        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);    }    public void setCamera(Camera camera)    {        mCamera = camera;        if (mCamera != null)        {            mSupportedPreviewSizes = mCamera.getParameters()                    .getSupportedPreviewSizes();            requestLayout();        }    }    @Override    public void surfaceCreated(SurfaceHolder holder)    {        Log.d(AppConstants.LOG_TAG, "surfaceCreated");        // The Surface has been created, now tell the camera where to draw the        // preview.        try        {            if (null != mCamera)            {                mCamera.setPreviewDisplay(holder);            }        }        catch (IOException e1)        {            e1.printStackTrace();            Log.d(AppConstants.LOG_TAG,                    "Error setting camera preview display: " + e1.getMessage());        }        try        {            if (null != mCamera)            {                mCamera.startPreview();            }            Log.d(AppConstants.LOG_TAG, "surfaceCreated successfully! ");        }        catch (Exception e)        {            Log.d(AppConstants.LOG_TAG,                    "Error setting camera preview: " + e.getMessage());        }    }    @Override    public void surfaceChanged(SurfaceHolder holder, int format, int width,            int height)    {        Log.d(AppConstants.LOG_TAG, "surface changed");        // If your preview can change or rotate, take care of those events here.        // Make sure to stop the preview before resizing or reformatting it.        if (null == mHolder.getSurface())        {            // preview surface does not exist            return;        }        // stop preview before making changes        try        {            if (null != mCamera)            {                mCamera.stopPreview();            }        }        catch (Exception e)        {            // ignore: tried to stop a non-existent preview        }        // set preview size and make any resize, rotate or        // reformatting changes here        if (null != mCamera)        {            Camera.Parameters parameters = mCamera.getParameters();            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);            requestLayout();            mCamera.setParameters(parameters);            mCamera.setDisplayOrientation(90);            Log.d(AppConstants.LOG_TAG, "camera set parameters successfully!: "                    + parameters);        }        // 这里可以用来设置尺寸        // start preview with new settings        try        {            if (null != mCamera)            {                mCamera.setPreviewDisplay(mHolder);                mCamera.startPreview();            }        }        catch (Exception e)        {            Log.d(AppConstants.LOG_TAG,                    "Error starting camera preview: " + e.getMessage());        }    }    @Override    public void surfaceDestroyed(SurfaceHolder holder)    {        Log.d(AppConstants.LOG_TAG, "surfaceDestroyed");        if (null != mCamera)        {            mCamera.stopPreview();        }    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)    {        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        // We purposely disregard child measurements because act as a        // wrapper to a SurfaceView that centers the camera preview instead        // of stretching it.        final int width = resolveSize(getSuggestedMinimumWidth(),                widthMeasureSpec);        final int height = resolveSize(getSuggestedMinimumHeight(),                heightMeasureSpec);        setMeasuredDimension(width, height);        if (mSupportedPreviewSizes != null)        {            mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width,                    height);        }    }    private Size getOptimalPreviewSize(List<Size> sizes, int w, int h)    {        final double ASPECT_TOLERANCE = 0.1;        double targetRatio = (double) w / h;        if (sizes == null)            return null;        Size optimalSize = null;        double minDiff = Double.MAX_VALUE;        int targetHeight = h;        // Try to find an size match aspect ratio and size        for (Size size : sizes)        {            double ratio = (double) size.width / size.height;            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE)                continue;            if (Math.abs(size.height - targetHeight) < minDiff)            {                optimalSize = size;                minDiff = Math.abs(size.height - targetHeight);            }        }        // Cannot find the one match the aspect ratio, ignore the requirement        if (optimalSize == null)        {            minDiff = Double.MAX_VALUE;            for (Size size : sizes)            {                if (Math.abs(size.height - targetHeight) < minDiff)                {                    optimalSize = size;                    minDiff = Math.abs(size.height - targetHeight);                }            }        }        return optimalSize;    }}

package com.example.hellocustomcamera;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.text.SimpleDateFormat;import java.util.Date;import android.app.Activity;import android.content.Context;import android.content.pm.PackageManager;import android.hardware.Camera;import android.hardware.Camera.CameraInfo;import android.hardware.Camera.PictureCallback;import android.os.Bundle;import android.os.Environment;import android.util.Log;import android.view.Display;import android.view.View;import android.view.Window;import android.view.WindowManager;import android.widget.Button;import android.widget.FrameLayout;import android.widget.Toast;public class HelloCustomCameraActivity extends Activity{    private Camera mCamera;    private CameraPreview mPreview;    int mNumberOfCameras;    int mCameraCurrentlyLocked;    // The first rear facing camera    int mDefaultCameraId;    int mScreenWidth, mScreenHeight;    @Override    public void onCreate(Bundle savedInstanceState)    {        Log.d(AppConstants.LOG_TAG, "onCreate");        super.onCreate(savedInstanceState);        // 无标题栏的窗口        requestWindowFeature(Window.FEATURE_NO_TITLE);        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);        // 设置布局        setContentView(R.layout.activity_hello_custom_camera);        // 得到屏幕的大小        WindowManager wManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE);        Display display = wManager.getDefaultDisplay();        mScreenHeight = display.getHeight();        mScreenWidth = display.getWidth();        // Create our Preview view and set it as the content of our activity.        mPreview = new CameraPreview(this);        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);        // 将相机预览图加入帧布局里面        preview.addView(mPreview, 0);        // 使用按钮进行拍摄动作监听        Button captureButton = (Button) findViewById(R.id.button_capture);        captureButton.setOnClickListener(new View.OnClickListener()        {            @Override            public void onClick(View v)            {                // get an image from the camera                mCamera.takePicture(null, null, mPicture);            }        });        // 得到默认的相机ID        mDefaultCameraId = getDefaultCameraId();        mCameraCurrentlyLocked = mDefaultCameraId;    }    @Override    protected void onResume()    {        Log.d(AppConstants.LOG_TAG, "onResume");        super.onResume();        // Open the default i.e. the first rear facing camera.        mCamera = getCameraInstance(mCameraCurrentlyLocked);                mPreview.setCamera(mCamera);    }    @Override    protected void onPause()    {        Log.d(AppConstants.LOG_TAG, "onPause");        super.onPause();        // Because the Camera object is a shared resource, it's very        // important to release it when the activity is paused.        if (mCamera != null)        {            mPreview.setCamera(null);            Log.d(AppConstants.LOG_TAG, "onPause --> Realease camera");            mCamera.release();            mCamera = null;        }    }    @Override    protected void onDestroy()    {        Log.d(AppConstants.LOG_TAG, "onDestroy");        super.onDestroy();    }    /**     * 得到默认相机的ID     *      * @return     */    private int getDefaultCameraId()    {        Log.d(AppConstants.LOG_TAG, "getDefaultCameraId");        int defaultId = -1;        // Find the total number of cameras available        mNumberOfCameras = Camera.getNumberOfCameras();        // Find the ID of the default camera        CameraInfo cameraInfo = new CameraInfo();        for (int i = 0; i < mNumberOfCameras; i++)        {            Camera.getCameraInfo(i, cameraInfo);            Log.d(AppConstants.LOG_TAG, "camera info: " + cameraInfo.orientation);            if (cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK)            {                defaultId = i;            }        }        if (-1 == defaultId)        {            if (mNumberOfCameras > 0)            {                // 如果没有后向摄像头                defaultId = 0;            }            else            {                // 没有摄像头                Toast.makeText(getApplicationContext(), R.string.no_camera,                        Toast.LENGTH_LONG).show();            }        }        return defaultId;    }    /** A safe way to get an instance of the Camera object. */    public static Camera getCameraInstance(int cameraId)    {        Log.d(AppConstants.LOG_TAG, "getCameraInstance");        Camera c = null;        try        {            c = Camera.open(cameraId); // attempt to get a Camera instance        }        catch (Exception e)        {            // Camera is not available (in use or does not exist)            e.printStackTrace();            Log.e(AppConstants.LOG_TAG, "Camera is not available");        }        return c; // returns null if camera is unavailable    }    public static final int MEDIA_TYPE_IMAGE = 1;    public static final int MEDIA_TYPE_VIDEO = 2;    /** Create a File for saving an image or video */    private static File getOutputMediaFile(int type)    {        Log.d(AppConstants.LOG_TAG, "getOutputMediaFile");        // To be safe, you should check that the SDCard is mounted        // using Environment.getExternalStorageState() before doing this.        File mediaStorageDir = null;        try        {            // This location works best if you want the created images to be            // shared            // between applications and persist after your app has been            // uninstalled.            mediaStorageDir = new File(                    Environment                            .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),                    "MyCameraApp");            Log.d(AppConstants.LOG_TAG,                    "Successfully created mediaStorageDir: " + mediaStorageDir);        }        catch (Exception e)        {            e.printStackTrace();            Log.d(AppConstants.LOG_TAG, "Error in Creating mediaStorageDir: "                    + mediaStorageDir);        }        // Create the storage directory if it does not exist        if (!mediaStorageDir.exists())        {            if (!mediaStorageDir.mkdirs())            {                // 在SD卡上创建文件夹需要权限：                // <uses-permission                // android:name="android.permission.WRITE_EXTERNAL_STORAGE" />                Log.d(AppConstants.LOG_TAG,                        "failed to create directory, check if you have the WRITE_EXTERNAL_STORAGE permission");                return null;            }        }        // Create a media file name        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss")                .format(new Date());        File mediaFile;        if (type == MEDIA_TYPE_IMAGE)        {            mediaFile = new File(mediaStorageDir.getPath() + File.separator                    + "IMG_" + timeStamp + ".jpg");        }        else if (type == MEDIA_TYPE_VIDEO)        {            mediaFile = new File(mediaStorageDir.getPath() + File.separator                    + "VID_" + timeStamp + ".mp4");        }        else        {            return null;        }        return mediaFile;    }    private PictureCallback mPicture = new PictureCallback()    {        @Override        public void onPictureTaken(byte[] data, Camera camera)        {            Log.d(AppConstants.LOG_TAG, "onPictureTaken");            File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);            if (pictureFile == null)            {                Log.d(AppConstants.LOG_TAG,                        "Error creating media file, check storage permissions: ");                return;            }            try            {                FileOutputStream fos = new FileOutputStream(pictureFile);                fos.write(data);                fos.close();            }            catch (FileNotFoundException e)            {                Log.d(AppConstants.LOG_TAG, "File not found: " + e.getMessage());            }            catch (IOException e)            {                Log.d(AppConstants.LOG_TAG,                        "Error accessing file: " + e.getMessage());            }            // 拍照后重新开始预览            mCamera.stopPreview();            mCamera.startPreview();        }    };    /** Check if this device has a camera */    private boolean checkCameraHardware(Context context)    {        if (context.getPackageManager().hasSystemFeature(                PackageManager.FEATURE_CAMERA))        {            // this device has a camera            return true;        }        else        {            // no camera on this device            return false;        }    }}

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <FrameLayout        android:id="@+id/camera_preview"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_weight="1" >    <Button        android:id="@+id/button_capture"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="bottom|center"        android:text="Capture" />    </FrameLayout></LinearLayout>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.hellocustomcamera"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk        android:minSdkVersion="9"        android:targetSdkVersion="15" />    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />    <uses-permission android:name="android.permission.CAMERA" />    <uses-feature android:name="android.hardware.camera" />    <application        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <activity            android:name=".HelloCustomCameraActivity"            android:label="@string/title_activity_hello_custom_camera" >            <!-- android:screenOrientation="landscape" -->            <!-- configure this activity to use landscape orientation -->            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

参考资料

　　Reference: Camera

　　http://developer.android.com/reference/android/hardware/Camera.html

　　相机参数：

　　http://developer.android.com/reference/android/hardware/Camera.Parameters.html

　　API Guides: Camera

　　http://developer.android.com/guide/topics/media/camera.html

　　API Demos:

　　com.example.android.apis.graphics包下的CameraPreview

　　实例教程：Android设备功能之Camera教程篇：

　　http://www.eoeandroid.com/thread-167870-1-1.html