編輯:關於Android編程
要自己寫一個相機應用直接使用相機硬件,首先應用需要一個權限設置,在AndroidManifest.xml中加上使用設備相機的權限:
為你的應用創建自定義的相機,一般步驟如下:
1.檢測相機硬件並獲取訪問
2.建立一個Preview類:需要一個相機預覽的類,繼承 SurfaceView
類,並實現SurfaceHolder接口。
3.建立預覽的布局。
4.為拍照建立監聽。
5.拍照並且存儲文件。
6.釋放相機。
因為相機是一個共享資源,所以應該被謹慎管理,這樣應用之間才不會發生沖突。
所以使用完相機之後應該調用 Camera.release()
來釋放相機對象。
如果不釋放,後續的使用相機請求(其他應用或本應用)都會失敗。
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; } }
設備上可能有多個相機,Android 2.3以後可以使用 Camera.getNumberOfCameras()
來查看相機的數目。
如下面這段程序用於檢測設備中的相機,並得到默認相機的索引號:
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) { // 如果沒有後向攝像頭 defaultId = 0; } else { // 沒有攝像頭 Toast.makeText(getApplicationContext(), R.string.no_camera, Toast.LENGTH_LONG).show(); } } return defaultId; }看了Camera類的代碼實現後,其中不帶參數的open()方法:默認是調用後置攝像頭
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; }
要獲取主要的相機,可以使用 Camera.open()
方法,注意異常處理。
在使用這個方法的時候一定要檢查異常,如果相機正在被使用或者不存在,沒有處理異常,將會使得應用被系統關閉。
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之後,可以使用Camera.open(int)來獲取特定的相機。
可以使用Camera.getParameters()方法來檢查相機的特性。
API Level 9之後,可以使用 Camera.getCameraInfo()
來查看相機是在設備前面還是後面,還可以得到圖像的方向。
為了有效地拍照或錄像,用戶必須要看到相機能看到的圖像。
相機的preview類是一個 SurfaceView
,展示了相機正在捕捉的圖像。
下面是一個預覽類的例子(來自官網):
/** 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()); } } }
注意要設置尺寸的話需要放在surfaceChanged()方法裡,調用 setPreviewSize()
方法,並且應該使用 getSupportedPreviewSizes()
返回的值,而不要使用任意的尺寸。
布局時可以使用FrameLayout,這樣其他的按鈕或者元素可以疊加在預覽圖像上。
對於大多數設備來說,相機預覽的默認方向是橫放的(landscape)。
從Android 2.2 (API Level 8)開始,可以使用 setDisplayOrientation()
來設置預覽圖像的方向。
如果需要在用戶改變設備方向的時候改變預覽圖像的方向,可以在 surfaceChanged()
方法中,首先用 Camera.stopPreview()
停止預覽,改變方向,然後用Camera.startPreview()開啟新的預覽。
當然你也可以直接在manifest中設置好方向,如下:
在應用裡面,必須為用戶控制加上監聽,來響應用戶拍照的動作。
為了得到圖像,要使用 Camera.takePicture()
方法。
這個方法接收三個參數,用於從相機獲取圖像。
為了接收到JPEG格式的數據,需要實現Camera.PictureCallback接口用來接收圖像數據並且寫入文件。
下面的代碼展示了一個最基本的實現:
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()); } } };
// 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); } } );
相機是設備資源,被所有應用共享,當應用不使用相機時應當及時釋放,應當在Activity.onPause()中釋放。
如果不及時釋放,後續的相機請求(包括你自己的應用和其他的應用發出的)都將失敗並且導致應用退出。
完整的照相程序需要考慮相機切換、預覽圖像的尺寸設置、焦距變換、縮放、白平衡的相機參數設置。
請查閱文後的參考資料進行進一步學習。
附上一個粗糙待完善的自定義相機程序(2013/4/6)
預覽圖像類:
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; /** * 相機圖片預覽類 * * @author * */ public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback { private SurfaceHolder mHolder; private Camera mCamera; Size mPreviewSize; ListmSupportedPreviewSizes; 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); } // 這裡可以用來設置尺寸 // 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 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); // 無標題欄的窗口 requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN); // 設置布局 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); // 將相機預覽圖加入幀布局裡面 preview.addView(mPreview, 0); // 使用按鈕進行拍攝動作監聽 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); } }); // 得到默認的相機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(); } /** * 得到默認相機的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) { // 如果沒有後向攝像頭 defaultId = 0; } else { // 沒有攝像頭 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卡上創建文件夾需要權限: //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()); } // 拍照後重新開始預覽 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; } } }
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