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 button Button 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