Android的照相機預覽功能(Camera Preview)

這是一個最簡單的照相機預覽功能的示範: 在佈局設置一個SurfaceView提供預覽功能; 本應用程式只能預覽, 並不支持其他如拍照等功能.




首先, 修改AndroidManifest.xml授予使用照相機權限, "android.permission.CAMERA".

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.AndroidCameraPreview"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".AndroidCameraPreview"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
    <uses-sdk android:minSdkVersion="7" />
    <uses-permission android:name="android.permission.CAMERA"></uses-permission>
</manifest> 

修改佈局(main.xml), 添加一個SurfaceView.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<SurfaceView
    android:id="@+id/previewsurface" 
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    />
</LinearLayout>

主要代碼, AndroidCameraPreview.java

package com.AndroidCameraPreview;

import java.io.IOException;

import android.app.Activity;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class AndroidCameraPreview extends Activity implements SurfaceHolder.Callback{
 
 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.main);
        
        getWindow().setFormat(PixelFormat.UNKNOWN);      
        previewSurfaceView = (SurfaceView)findViewById(R.id.previewsurface);
        previewSurfaceHolder = previewSurfaceView.getHolder();
        previewSurfaceHolder.addCallback(this);
        previewSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

 @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);
   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();
 }

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

主活動(AndroidCameraPreview)定義為extends Activity implements SurfaceHolder.Callback, 所以，我們必須重寫surfaceCreated(), surfaceChanged()和surfaceDestroyed()方法. 這裡亦是實現照相機預覽功能的主要部分.
以及, 需要在onCreate()方法中先設置我們的SurfaceHolder.


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