Android应用开发提高篇（5）Camera使用

一、概述

      Camera是手机的一个很重要的设备，可以说现在的每一部手机上都有。回想当时在Linux搞摄像头编程真的要捏一把汗。有人会说在Linux下装个opencv就可以通过它的函数来使用摄像头啦，但我并没有这么做，我还是用最原始的方法（V4L2）实现了。之前研究过Android关于摄像头这部分的源码，毫无疑问，Android关于摄像头底层的实现用的也是V4L2。

二、实现

     新建工程MyCamera，修改/res/layout/main.xml文件，使用RelativeLayout布局，并添加一个SurfaceView和一个Button，完整的main.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"   
    >
     
    <SurfaceView 
        android:id="@+id/surfaceview"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_above="@+id/button"
        />
    
    <Button 
        android:id="@+id/button"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:text="拍照"
        />
        
</RelativeLayout>

接着，修改MyCameraActivity.java文件，实现了SurfaceHolder.Callback接口，用于初始化、释放摄像头和Camera.PictureCallback接口，用于保存图片数据到文件里。完整的内容如下：

package com.nan.camera;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.Bundle;
import android.os.Environment;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MyCameraActivity extends Activity 
{
    private SurfaceView mSurfaceView = null;
    private SurfaceHolder mSurfaceHolder = null;
    private Button takePictureButton = null;
    private Camera mCamera;
    //记录保存的是第几张图片
    private int whichPicture = 0;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        takePictureButton = (Button)this.findViewById(R.id.button);
        mSurfaceView = (SurfaceView)this.findViewById(R.id.surfaceview);
        mSurfaceHolder = mSurfaceView.getHolder();
        mSurfaceHolder.addCallback(new SurfaceHolderCallback());
        //设置缓冲区类型
        mSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);   
        //拍照按钮监听    
        takePictureButton.setOnClickListener(new View.OnClickListener() 
        {
            
            @Override
            public void onClick(View v) 
            {
                // TODO Auto-generated method stub
                //拍照
                mCamera.takePicture(null, null, pictureCallback);
            }
        });
         
    }
    
    private class SurfaceHolderCallback implements SurfaceHolder.Callback
    {

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width,
                int height) {
            // TODO Auto-generated method stub
            
        }

        @Override
        public void surfaceCreated(SurfaceHolder holder) 
        {
            // TODO Auto-generated method stub
            //打开摄像头
            mCamera = Camera.open();
            try {
                mCamera.setPreviewDisplay(mSurfaceHolder);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            //获取摄像头参数
            Camera.Parameters mParameters = mCamera.getParameters();
            //设置图片格式
            mParameters.setPictureFormat(PixelFormat.JPEG);
            mCamera.setParameters(mParameters); 
            //开始预览
            mCamera.startPreview();
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) 
        {
            // TODO Auto-generated method stub
            if(mCamera!=null)
            {
                //停止预览
                mCamera.stopPreview();
                //释放摄像头
                mCamera.release();
                mCamera = null;
            }
        }
        
    }
    
    //拍照回调
    private Camera.PictureCallback pictureCallback = new Camera.PictureCallback()
    {

        @Override
        public void onPictureTaken(byte[] data, Camera camera) 
        {
            // TODO Auto-generated method stub
            //停止预览
            mCamera.stopPreview();
            Bitmap mBitmap;
            mBitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
            //文件路径和文件名
            File pictureFile = new File(Environment.getExternalStorageDirectory(),"camera"+Integer.toString(whichPicture)+".jpg");    
            
            try 
            {
                FileOutputStream mFileOutputStream = new FileOutputStream(pictureFile);
                //将图像数据压入文件
                mBitmap.compress(Bitmap.CompressFormat.JPEG, 75, mFileOutputStream);
                try {
                    //关闭输出流
                    mFileOutputStream.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            } 
            catch (FileNotFoundException e) 
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }        
            displayToast("保存成功！");
            whichPicture++;
            //开始预览
            mCamera.startPreview();
        }
        
    }; 
    
    //显示Toast函数
    private void displayToast(String s)
    {
        Toast.makeText(this, s, Toast.LENGTH_SHORT).show();
    }
      
}

在真机上运行该程序：

按一下“拍照”按钮：

图片会被保存到sd卡的根目录下面。