Android Camera开发详解 一 实现一个可复用的相机组件

若自己的应用需要使用camera，有两种解决方案。

1. 使用Intent调用自带的Camera程序

2. 使用Camera API在程序中构造自己的Camera。

本文主要讲解第二种。

 

构造一个相机APP，通常需要六个步骤

1. 声明Manifest的相机权限

2. 创建一个相机预览类（继承SurfaceView）

3. 创建一个类实现相机拍照之后的回调函数

 

本文将一步步带你实现上述三个步骤。

1. 声明Manifest的相机权限。

应为我们需要写文件与调用相机，所以在你的manifest文件中加上。

<uses-permission android:name="android.permission.CAMERA" />

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

 

2. 创建一个相机预览类

由于相机的预览是使用的SurfaceView，所以这里我们创建一个SurfaceView的子类。

为了让这个View所见即所得，我们将其设置为4/3的比例。重写它的onMeasure方法

代码如下：

package com.example.cameratutorial;

import android.content.Context;

import android.util.Log;
import android.view.SurfaceView;

/**
* @author CTGU小龙同学 2014-6-21
*/
public class CameraSurfaceView extends SurfaceView {
private static final String TAG = "CameraSurfaceView";
// 用四比三的比例
public static double RATIO = 3.0 / 4.0;

/**
* @param context
*/
public CameraSurfaceView(Context context) {
super(context);

}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

int height = MeasureSpec.getSize(heightMeasureSpec);
int width = MeasureSpec.getSize(widthMeasureSpec);
Log.d("Measured", "before width" + width + "height" + height);

boolean isWidthLonger;
int longSide;
int shortSide;
// 以短边为准确定一下长边
if (width < height) {
height = (int) (width / RATIO);
isWidthLonger = false;

} else {
width = (int) (height / RATIO);
isWidthLonger = true;
}

Log.d("Measured", "after width" + width + "height" + height);
setMeasuredDimension(width, height);

}

}
3. 现在我们使用一个实现了SurfaceHolder.Callback, Camera.PictureCallback 的Fragment来把我们需要的组件都封装起来。

代码如下：

package com.example.cameratutorial;

import java.io.*;
import java.util.*;
import android.app.Activity;
import android.app.Fragment;
import android.graphics.*;

import android.graphics.Bitmap.CompressFormat;
import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.hardware.Camera.Size;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.*;

import android.widget.RelativeLayout;
import android.widget.Toast;

/**
* @author CTGU小龙同学 2014-6-21
*/
public class CameraFragment extends Fragment implements SurfaceHolder.Callback, Camera.PictureCallback {
private Camera mCamera;
// CameraPreview的holder
private SurfaceHolder mSurfaceHolder;
private CameraSurfaceView preview;
private int mFrontCameraId = -1;
private int mBackCameraId = -1;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

preview = new CameraSurfaceView(getActivity());
preview.getHolder().addCallback(this);

RelativeLayout layout = new RelativeLayout(getActivity());
layout.addView(preview);

return layout;

}

@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
findAvailableCameras();

}

@Override
public void onResume() {

super.onResume();
Log.d("camera", "mFrontCameraId" + mFrontCameraId);
Log.d("camera", "mbackCameraId" + mBackCameraId);
if (mBackCameraId != -1) {

mCamera = Camera.open(mBackCameraId);

} else {
Toast.makeText(getActivity(), "fialed to open camera", Toast.LENGTH_SHORT).show();
}

}

@Override
public void onPause() {
super.onPause();

mCamera.stopPreview();
mCamera.release();
}

/**
* 获得可用的相机，并设置前后摄像机的ID
*/
private void findAvailableCameras() {

Camera.CameraInfo info = new CameraInfo();
int numCamera = Camera.getNumberOfCameras();
for (int i = 0; i < numCamera; i++) {
Camera.getCameraInfo(i, info);
// 找到了前置摄像头
if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
mFrontCameraId = info.facing;
}
// 招到了后置摄像头
if (info.facing == Camera.CameraInfo.CAMERA_FACING_BACK) {
mBackCameraId = info.facing;
}

}

}

/**
* 当相机拍照时会回调该方法
*/
@Override
public void onPictureTaken(byte[] data, Camera camera) {
final Bitmap bitmap;

final String path;
try {
// /storage/emulated/0/Pictures/XXX.jpg

path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath() + "/" + new Date().toLocaleString() + ".jpg";
Log.d("Path", path);
bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
camera.stopPreview();

final int displayOrientation = getCorrectOrientation();
new Thread(new Runnable() {

@Override
public void run() {
FileOutputStream fos;
Matrix matrix = new Matrix();
matrix.postRotate(displayOrientation);
Bitmap rotaBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false);

try {
fos = new FileOutputStream(path);
rotaBitmap.compress(CompressFormat.JPEG, 100, fos);
fos.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}).start();

} catch (Exception e) {

}
camera.startPreview();
}

/**
* 让预览跟照片符合正确的方向。<br/>
* 因为预览默认是横向的。如果是一个竖向的应用，就需要把预览转90度<br/>
* 比如横着时1280*960的尺寸时，1280是宽.<br/>
* 竖着的时候1280就是高了<br/>
* 这段代码来自官方API。意思就是让拍出照片的方向和预览方向正确的符合设备当前的方向（有可能是竖向的也可能使横向的）
*
*/
private int getCorrectOrientation() {
android.hardware.Camera.CameraInfo info = new android.hardware.Camera.CameraInfo();
android.hardware.Camera.getCameraInfo(mBackCameraId, info);
int rotation = getActivity().getWindowManager().getDefaultDisplay().getRotation();
int degrees = 0;
switch (rotation) {
case Surface.ROTATION_0:
degrees = 0;
break;
case Surface.ROTATION_90:
degrees = 90;
break;
case Surface.ROTATION_180:
degrees = 180;
break;
case Surface.ROTATION_270:
degrees = 270;
break;
}

int result;
if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
result = (info.orientation + degrees) % 360;
result = (360 - result) % 360; // compensate the mirror
} else { // back-facing
result = (info.orientation - degrees + 360) % 360;
}
Log.d("orientationResult", result + "");
return result;
}

public void takePicture() {
mCamera.takePicture(null, null, this);
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
mSurfaceHolder = holder;

startPreView();

}

private void startPreView() {
try {
mCamera.setPreviewDisplay(mSurfaceHolder);
setPreviewSize();
setDisplayOrientation();
mCamera.startPreview();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

private void setDisplayOrientation() {
int displayOrientation = getCorrectOrientation();

mCamera.setDisplayOrientation(displayOrientation);
}

/**
* 我们用4比3的比例设置预览图片
*/
private void setPreviewSize() {
Camera.Parameters params = mCamera.getParameters();
List<Size> sizes = params.getSupportedPreviewSizes();
for (Size size : sizes) {
Log.d("previewSize", "width:" + size.width + " height " + size.height);
}
for (Size size : sizes) {
if (size.width / 4 == size.height / 3) {
params.setPreviewSize(size.width, size.height);
Log.d("previewSize", "SET width:" + size.width + " height " + size.height);
break;
}
}

// params一定要记得写回Camera
mCamera.setParameters(params);

}

private void setPictureSize() {
Camera.Parameters params = mCamera.getParameters();
List<Size> sizes = params.getSupportedPictureSizes();
for (Size size : sizes) {
Log.d("picSize", "width:" + size.width + " height " + size.height);
}
for (Size size : sizes) {
if (size.width / 4 == size.height / 3) {
params.setPictureSize(size.width, size.height);
break;
}
}

}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
mCamera.release();
}

}

4. 程序的Mainactivity以及相应的布局文件

package com.example.cameratutorial;

import android.os.Bundle;
import android.app.Activity;
import android.app.FragmentManager;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final CameraFragment fragment=(CameraFragment) getFragmentManager().findFragmentById(R.id.camera_fragment);
Button button=(Button) findViewById(R.id.TakePic);
button.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
fragment.takePicture();

}
});

}

}

布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>

<fragment
android:id="@+id/camera_fragment"
android:name="com.example.cameratutorial.CameraFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>

<Button
android:id="@+id/TakePic"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:text="capture" />

</RelativeLayout>

这样，我们一个可以复用的相机组件就完成了

下一篇文章应该是关于如何实现触摸对焦测光的。