相機預覽與方向性

在Android默認情況，當“屏幕方向”或“鍵盤顯示隱藏”變化時都會銷毀當前Activity，創建新的Activity。如果不希望重新創建Activity實例，可以在AndroidManifest.xml中配置
Activity：
<activity android:name=".MainActivity" android:configChanges="keyboardHidden|orientation" >
這樣就不會銷毀重建了在配置了這個屬性後，android:configChanges 屬性就會捕獲“屏幕方向”和“鍵盤顯示隱藏”變化，當捕獲到這些變化後會調用Activity的onConfigurationChanged()方法。

我在手機上調試發現橫豎屏切換時，並沒有執行onConfigurationChanged()方法，但是Activity卻執行了銷毀重建的過程這是為什麼呢？這是因為版本的問題上面的配置只在android4.o之前的版本起作用，在android 4.0 以上不起作用，必須要加上screenSize,也就是說android 4.0以後的版本必須這樣配置android:configChanges=" keyboardHidden|orientation|screenSize"

下面我們結合實例說orientation和onConfigurationChanaged方法

代碼：

          <activity
            android:name=".MainActivity"
            android:configChanges="orientation|keyboardHidden|screenSize"
            android:screenOrientation="landscape"
            >

AndroidManifest.xml 中加上 permission 和 feature

        
     
<uses-permission android:name="android.permission.CAMERA">
<uses-feature android:name="android.hardware.camera">
<uses-feature android:name="android.hardware.camera.autofocus">

另外使用Camera API拍照或攝像，都需要用到預覽，預覽就要用到SurfaceView，為此Activity的佈局中必須有SurfaceView。

   
<SurfaceView
 android:id="@+id/surfaceView1"
 android:layout_width="320px"
 android:layout_height="240px">
</SurfaceView>

code:

   
package com.example.cheng.camera_for_led;

import android.app.Activity;
import android.content.res.Configuration;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import java.io.IOException;
import static android.hardware.Camera.getNumberOfCameras;

public class MainActivity extends Activity implements SurfaceHolder.Callback,Camera.PreviewCallback {
    private static final String TAG = "My_CAMERA";
    Camera myCamera;
    SurfaceView previewSurfaceView;
    SurfaceHolder previewSurfaceHolder;
    boolean previewing = false;

    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getWindow().setFormat(PixelFormat.UNKNOWN);

        previewSurfaceView = (SurfaceView) findViewById(R.id.previewsurface);
        previewSurfaceHolder = previewSurfaceView.getHolder();// 绑定SurfaceView，取得SurfaceHolder对象
        previewSurfaceHolder.addCallback(this);//SurfaceHolder加入回调接口
        previewSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);// 設置顯示器類型，setType必须设置
    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub

        if (previewing) {
            myCamera.stopPreview();
            previewing = false;
        }
        try {
            myCamera.setPreviewDisplay(arg0);
            //Camera.Parameters parameters = myCamera.getParameters();
            Log.d(TAG, "ttttt");
            myCamera.startPreview();
            previewing = true;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {
        // TODO Auto-generated method stub
        myCamera = Camera.open();//开启摄像头（2.3版本后支持多摄像头,需传入参数）
        int a = getNumberOfCameras();
        Log.d(TAG+" number = ", String.valueOf(a));
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {
        // TODO Auto-generated method stub
        myCamera.stopPreview();
        myCamera.release();
        myCamera = null;
        previewing = false;
    }

    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {

    }
    //当指定了android:configChanges="orientation"后,方向改变时onConfigurationChanged被调用,并且activity不再销毁重建
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        switch (newConfig.orientation) {
            case Configuration.ORIENTATION_PORTRAIT://竖屏
                Log.i(TAG,"竖屏");
                // setContentView(R.layout.activity_main);
                myCamera.setDisplayOrientation(0); // 在2.2以上可以使用
                break;
            case Configuration.ORIENTATION_LANDSCAPE://横屏
                Log.i(TAG,"横屏");
                myCamera.setDisplayOrientation(90); // 在2.2以上可以使用
                //setContentView(R.layout.activity_main);
            default:
                break;
        }
    }
    //Activity创建或者从后台重新回到前台时被调用
    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG,"执行了onStart方法");
    }
    //Activity从后台重新回到前台时被调用
    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG,"执行了onRestart方法");
    }
    //Activity创建或者从被覆盖、后台重新回到前台时被调用
    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG,"执行了onResume方法");
    }
    //Activity被覆盖到下面或者锁屏时被调用
    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG,"执行了onPause方法");
    }
    //退出当前Activity或者跳转到新Activity时被调用
    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG,"执行了onStop方法");
    }
    //退出当前Activity时被调用,调用之后Activity就结束了
    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG,"执行了onDestroy方法");
    }
}

Reference:

   
http://simonxanderandroid.blogspot.tw/2011/02/android-camera.html
http://stackoverflow.com/questions/8242749/how-to-set-androidscreenorientation-portrait-for-camera
http://www.kancloud.cn/digest/singwhiledrinking/122022
http://www.cnblogs.com/skyseraph/archive/2012/03/26/2418665.html