Android Camera 相机程序编写
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。
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：
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;
}
说明open方法默认是打开第一个后向摄像头的。
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。
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。
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。
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>
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);
}
}
);
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。
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;
}
}
主要的Activity类：
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;
}
}
}
布局文件：
<?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文件：
<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>
三星S5660上测试可以拍照用，其他手机未知。
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
http://www.cnblogs.com/mengdd/archive/2013/04/06/3002975.html
