【移动应用开发技术】Android Camera2怎么实现预览功能

【移动应用开发技术】AndroidCamera2怎么实现预览功能

这篇文章主要介绍AndroidCamera2怎么实现预览功能，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！1.概述最近在做一些关于人脸识别的项目，需要用到Android相机的预览功能。网上查阅相关资料后，发现Android5.0及以后的版本中，原有的CameraAPI已经被Camera2API所取代。全新的Camera2在Camera的基础上进行了改造，大幅提升了Android系统的拍照功能。它通过以下几个类与方法来实现相机预览时的工作过程：•CameraManager：摄像头管理器，主要用于检测系统摄像头、打开系统摄像头等；•CameraDevice:用于描述系统摄像头，可用于关闭相机、创建相机会话、发送拍照请求等；•CameraCharacteristics：用于描述摄像头所支持的各种特性；•CameraCaptureSession：当程序需要预览、拍照时，都需要先通过CameraCaptureSession来实现。该会话通过调用方法setRepeatingRequest()实现预览；•CameraRequest：代表一次捕获请求，用于描述捕获图片的各种参数设置；•CameraRequest.Builder：负责生成CameraRequest对象。2.相机预览下面通过源码来讲解如何使用Camera2来实现相机的预览功能。2.1相机权限设置<uses-permission

android:name="android.permission.CAMERA"

/>2.2App布局•activity_main.xml<?xml

version="1.0"

encoding="utf-8"?>

<FrameLayout

xmlns:android="/apk/res/android"

xmlns:tools="/tools"

android:id="@+id/container"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:background="#000"

tools:context=".MainActivity">

</FrameLayout>

•fragment_camera.xml

<?xml

version="1.0"

encoding="utf-8"?>

<RelativeLayout

xmlns:android="/apk/res/android"

xmlns:tools="/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context=".CameraFragment">

<com.lightweh.camera2preview.AutoFitTextureView

android:id="@+id/textureView"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_centerVertical="true"

android:layout_centerHorizontal="true"

/>

</RelativeLayout>2.3相机自定义Viewpublic

class

AutoFitTextureView

extends

TextureView

{

private

int

mRatioWidth

=

0;

private

int

mRatioHeight

=

0;

public

AutoFitTextureView(Context

context)

{

this(context,

null);

}

public

AutoFitTextureView(Context

context,

AttributeSet

attrs)

{

this(context,

attrs,

0);

}

public

AutoFitTextureView(Context

context,

AttributeSet

attrs,

int

defStyle)

{

super(context,

attrs,

defStyle);

}

public

void

setAspectRatio(int

width,

int

height)

{

if

(width

<

0

||

height

<

0)

{

throw

new

IllegalArgumentException("Size

cannot

be

negative.");

}

mRatioWidth

=

width;

mRatioHeight

=

height;

requestLayout();

}

@Override

protected

void

onMeasure(int

widthMeasureSpec,

int

heightMeasureSpec)

{

super.onMeasure(widthMeasureSpec,

heightMeasureSpec);

int

width

=

MeasureSpec.getSize(widthMeasureSpec);

int

height

=

MeasureSpec.getSize(heightMeasureSpec);

if

(0

==

mRatioWidth

||

0

==

mRatioHeight)

{

setMeasuredDimension(width,

height);

}

else

{

if

(width

<

height

*

mRatioWidth

/

mRatioHeight)

{

setMeasuredDimension(width,

width

*

mRatioHeight

/

mRatioWidth);

}

else

{

setMeasuredDimension(height

*

mRatioWidth

/

mRatioHeight,

height);

}

}

}

}2.4动态申请相机权限public

class

MainActivity

extends

AppCompatActivity

{

private

static

final

int

REQUEST_PERMISSION

=

1;

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

if

(hasPermission())

{

if

(null

==

savedInstanceState)

{

setFragment();

}

}

else

{

requestPermission();

}

}

@Override

public

void

onRequestPermissionsResult(int

requestCode,

String

permissions[],

int[]

grantResults)

{

if

(requestCode

==

REQUEST_PERMISSION)

{

if

(grantResults.length

==

1

&&

grantResults[0]

==

PackageManager.PERMISSION_GRANTED)

{

setFragment();

}

else

{

requestPermission();

}

}

else

{

super.onRequestPermissionsResult(requestCode,

permissions,

grantResults);

}

}

//

权限判断，当系统版本大于23时，才有必要判断是否获取权限

private

boolean

hasPermission()

{

if

(Build.VERSION.SDK_INT

>=

Build.VERSION_CODES.M)

{

return

checkSelfPermission(Manifest.permission.CAMERA)

==

PackageManager.PERMISSION_GRANTED;

}

else

{

return

true;

}

}

//

请求相机权限

private

void

requestPermission()

{

if

(Build.VERSION.SDK_INT

>=

Build.VERSION_CODES.M)

{

if

(shouldShowRequestPermissionRationale(Manifest.permission.CAMERA))

{

Toast.makeText(MainActivity.this,

"Camera

permission

are

required

for

this

demo",

Toast.LENGTH_LONG).show();

}

requestPermissions(new

String[]{Manifest.permission.CAMERA},

REQUEST_PERMISSION);

}

}

//

启动相机Fragment

private

void

setFragment()

{

getSupportFragmentManager()

.beginTransaction()

.replace(R.id.container,

CameraFragment.newInstance())

.commitNowAllowingStateLoss();

}

}2.5开启相机预览首先，在onResume()中，我们需要开启一个HandlerThread，然后利用该线程的Looper对象构建一个Handler用于相机回调。@Override

public

void

onResume()

{

super.onResume();

startBackgroundThread();

//

When

the

screen

is

turned

off

and

turned

back

on,

the

SurfaceTexture

is

//

already

available,

and

"onSurfaceTextureAvailable"

will

not

be

called.

In

//

that

case,

we

can

open

a

camera

and

start

preview

from

here

(otherwise,

we

//

wait

until

the

surface

is

ready

in

the

SurfaceTextureListener).

if

(mTextureView.isAvailable())

{

openCamera(mTextureView.getWidth(),

mTextureView.getHeight());

}

else

{

mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);

}

}

private

void

startBackgroundThread()

{

mBackgroundThread

=

new

HandlerThread("CameraBackground");

mBackgroundThread.start();

mBackgroundHandler

=

new

Handler(mBackgroundThread.getLooper());

}同时，在onPause()中有对应的HandlerThread关闭方法。当屏幕关闭后重新开启，SurfaceTexture已经就绪，此时不会触发onSurfaceTextureAvailable回调。因此，我们判断mTextureView如果可用，则直接打开相机，否则等待SurfaceTexture回调就绪后再开启相机。private

void

openCamera(int

width,

int

height)

{

if

(ContextCompat.checkSelfPermission(getActivity(),

Manifest.permission.CAMERA)

!=

PackageManager.PERMISSION_GRANTED)

{

return;

}

setUpCameraOutputs(width,

height);

configureTransform(width,

height);

Activity

activity

=

getActivity();

CameraManager

manager

=

(CameraManager)

activity.getSystemService(Context.CAMERA_SERVICE);

try

{

if

(!mCameraOpenCloseLock.tryAcquire(2500,

TimeUnit.MILLISECONDS))

{

throw

new

RuntimeException("Time

out

waiting

to

lock

camera

opening.");

}

manager.openCamera(mCameraId,

mStateCallback,

mBackgroundHandler);

}

catch

(CameraAccessException

e)

{

e.printStackTrace();

}

catch

(InterruptedException

e)

{

throw

new

RuntimeException("Interrupted

while

trying

to

lock

camera

opening.",

e);

}

}开启相机时，我们首先判断是否具备相机权限，然后调用setUpCameraOutputs函数对相机参数进行设置（包括指定摄像头、相机预览方向以及预览尺寸的设定等），接下来调用configureTransform函数对预览图片的大小和方向进行调整，最后获取CameraManager对象开启相机。因为相机有可能会被其他进程同时访问，所以在开启相机时需要加锁。private

final

CameraDevice.StateCallback

mStateCallback

=

new

CameraDevice.StateCallback()

{

@Override

public

void

onOpened(@NonNull

CameraDevice

cameraDevice)

{

mCameraOpenCloseLock.release();

mCameraDevice

=

cameraDevice;

createCameraPreviewSession();

}

@Override

public

void

onDisconnected(@NonNull

CameraDevice

cameraDevice)

{

mCameraOpenCloseLock.release();

cameraDevice.close();

mCameraDevice

=

null;

}

@Override

public

void

onError(@NonNull

CameraDevice

cameraDevice,

int

error)

{

mCameraOpenCloseLock.release();

cameraDevice.close();

mCameraDevice

=

null;

Activity

activity

=

getActivity();

if

(null

!=

activity)

{

activity.finish();

}

}

};相机开启时还会指定相机的状态变化回调函数mStateCallback，如果相机成功开启，则开始创建相机预览会话。private

void

createCameraPreviewSession()

{

try

{

//

获取

texture

实例

SurfaceTexture

texture

=

mTextureView.getSurfaceTexture();

assert

texture

!=

null;

//

设置

TextureView

缓冲区大小

texture.setDefaultBufferSize(mPreviewSize.getWidth(),

mPreviewSize.getHeight());

//

获取

Surface

显示预览数据

Surface

surface

=

new

Surface(texture);

//

构建适合相机预览的请求

mPreviewRequestBuilder

=

mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

//

设置

surface

作为预览数据的显示界面

mPreviewRequestBuilder.addTarget(surface);

//

创建相机捕获会话用于预览

mCameraDevice.createCaptureSession(Arrays.asList(surface),

new

CameraCaptureSession.StateCallback()

{

@Override

pu