在本课程中，我们将讨论如何使用框架 API 直接控制相机硬件。

与从已有相机应用请求照片或视频相比，直接控制设备相机所需要的代码要多得多。不过，如果您要开发专门的相机应用或者与您的应用界面完全集成的应用，本课程将向您介绍具体操作方法。

请参阅以下相关资源：

打开 Camera 对象

获取

如果相机已被其他应用使用，则调用 try 块中。

Kotlin

private fun safeCameraOpen(id: Int): Boolean {

return try {

releaseCameraAndPreview()

mCamera = Camera.open(id)

true

} catch (e: Exception) {

Log.e(getString(R.string.app_name), "failed to open Camera")

e.printStackTrace()

false

}

}

private fun releaseCameraAndPreview() {

preview?.setCamera(null)

mCamera?.also { camera ->

camera.release()

mCamera = null

}

}Java

private boolean safeCameraOpen(int id) {

boolean qOpened = false;

try {

releaseCameraAndPreview();

camera = Camera.open(id);

qOpened = (camera != null);

} catch (Exception e) {

Log.e(getString(R.string.app_name), "failed to open Camera");

e.printStackTrace();

}

return qOpened;

}

private void releaseCameraAndPreview() {

preview.setCamera(null);

if (camera != null) {

camera.release();

camera = null;

}

}

从 API 级别 9 开始，相机框架支持多个摄像头。如果您使用的是旧版 API 并且调用不带参数的

创建相机预览

在拍摄照片时，用户通常要先看到拍摄目标的预览效果，然后再按下快门。为此，您可以使用

预览类

如需开始显示预览，您需要预览类。预览需要实现 android.view.SurfaceHolder.Callback 接口，该接口用于将图片数据从相机硬件传递到相机应用。

Kotlin

class Preview(

context: Context,

val surfaceView: SurfaceView = SurfaceView(context)

) : ViewGroup(context), SurfaceHolder.Callback {

var mHolder: SurfaceHolder = surfaceView.holder.apply {

addCallback(this@Preview)

setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS)

}

...

}Java

class Preview extends ViewGroup implements SurfaceHolder.Callback {

SurfaceView surfaceView;

SurfaceHolder holder;

Preview(Context context) {

super(context);

surfaceView = new SurfaceView(context);

addView(surfaceView);

// Install a SurfaceHolder.Callback so we get notified when the

// underlying surface is created and destroyed.

holder = surfaceView.getHolder();

holder.addCallback(this);

holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

}

...

}

您必须先将预览类传递给

设置并启动预览

您必须按特定顺序创建相机实例及其相关预览，其中相机对象位于第一位。在下面的代码段中，初始化相机的过程已经过封装，这样每当用户执行操作以更改相机时，setCamera() 方法都会调用 surfaceChanged() 回调方法中重启预览。

Kotlin

fun setCamera(camera: Camera?) {

if (mCamera == camera) {

return

}

stopPreviewAndFreeCamera()

mCamera = camera

mCamera?.apply {

mSupportedPreviewSizes = parameters.supportedPreviewSizes

requestLayout()

try {

setPreviewDisplay(holder)

} catch (e: IOException) {

e.printStackTrace()

}

// Important: Call startPreview() to start updating the preview

// surface. Preview must be started before you can take a picture.

startPreview()

}

}Java

public void setCamera(Camera camera) {

if (mCamera == camera) { return; }

stopPreviewAndFreeCamera();

mCamera = camera;

if (mCamera != null) {

List localSizes = mCamera.getParameters().getSupportedPreviewSizes();

supportedPreviewSizes = localSizes;

requestLayout();

try {

mCamera.setPreviewDisplay(holder);

} catch (IOException e) {

e.printStackTrace();

}

// Important: Call startPreview() to start updating the preview

// surface. Preview must be started before you can take a picture.

mCamera.startPreview();

}

}

修改相机设置

相机设置会更改相机拍照的方式(从缩放级别到曝光补偿)。此示例只会更改预览大小；请查看相机应用的源代码以了解更多信息。

Kotlin

override fun surfaceChanged(holder: SurfaceHolder, format: Int, w: Int, h: Int) {

mCamera?.apply {

// Now that the size is known, set up the camera parameters and begin

// the preview.

parameters?.also { params ->

params.setPreviewSize(previewSize.width, previewSize.height)

requestLayout()

parameters = params

}

// Important: Call startPreview() to start updating the preview surface.

// Preview must be started before you can take a picture.

startPreview()

}

}Java

@Override

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {

// Now that the size is known, set up the camera parameters and begin

// the preview.

Camera.Parameters parameters = mCamera.getParameters();

parameters.setPreviewSize(previewSize.width, previewSize.height);

requestLayout();

mCamera.setParameters(parameters);

// Important: Call startPreview() to start updating the preview surface.

// Preview must be started before you can take a picture.

mCamera.startPreview();

}

设置预览屏幕方向

大多数相机应用会将屏幕锁定为横屏模式，因为这是摄像头传感器的自然屏幕方向。此设置不会阻止您拍摄纵向模式的照片，因为设备的屏幕方向会记录在 EXIF 头文件中。通过

拍照

如果要连续抓取图片，您可以创建

重启预览

拍摄一张照片后，您必须重启预览，然后用户才能拍摄另一张照片。在下面的示例中，重启是通过过载快门按钮完成的。

Kotlin

fun onClick(v: View) {

previewState = if (previewState == K_STATE_FROZEN) {

camera?.startPreview()

K_STATE_PREVIEW

} else {

camera?.takePicture(null, rawCallback, null)

K_STATE_BUSY

}

shutterBtnConfig()

}Java

@Override

public void onClick(View v) {

switch(previewState) {

case K_STATE_FROZEN:

camera.startPreview();

previewState = K_STATE_PREVIEW;

break;

default:

camera.takePicture( null, rawCallback, null);

previewState = K_STATE_BUSY;

} // switch

shutterBtnConfig();

}

停止预览并释放相机

应用使用相机完成操作后，应该对相机进行清理。具体来说，您必须释放

应在何时停止预览并释放相机？如果预览表面遭到破坏，则明确表示您应该停止预览并释放相机(如 Preview 类中的下列方法所示)。

Kotlin

override fun surfaceDestroyed(holder: SurfaceHolder) {

// Surface will be destroyed when we return, so stop the preview.

// Call stopPreview() to stop updating the preview surface.

mCamera?.stopPreview()

}

/**

* When this function returns, mCamera will be null.

*/

private fun stopPreviewAndFreeCamera() {

mCamera?.apply {

// Call stopPreview() to stop updating the preview surface.

stopPreview()

// Important: Call release() to release the camera for use by other

// applications. Applications should release the camera immediately

// during onPause() and re-open() it during onResume()).

release()

mCamera = null

}

}Java

@Override

public void surfaceDestroyed(SurfaceHolder holder) {

// Surface will be destroyed when we return, so stop the preview.

if (mCamera != null) {

// Call stopPreview() to stop updating the preview surface.

mCamera.stopPreview();

}

}

/**

* When this function returns, mCamera will be null.

*/

private void stopPreviewAndFreeCamera() {

if (mCamera != null) {

// Call stopPreview() to stop updating the preview surface.

mCamera.stopPreview();

// Important: Call release() to release the camera for use by other

// applications. Applications should release the camera immediately

// during onPause() and re-open() it during onResume()).

mCamera.release();

mCamera = null;

}

}

如本课程前面所述，此过程也是 setCamera() 方法的一部分，因此要初始化相机，您必须先停止预览。