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  File Name     : FlashLightActivity.java

package com.richview.flashlight;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.Toast;

public class FlashLightActivity extends Activity {
    private Button onebutton = null;
    private Camera camera = null;
    private Parameters parameters = null;
    public static boolean kaiguan = true; //false :poweron, true:poweroff
    private int back = 0;//record the back key pressed times
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       
  getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD,WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
  getWindow().setFlags(WindowManager.LayoutParams.FLAG_HOMEKEY_DISPATCHED,WindowManager.LayoutParams.FLAG_HOMEKEY_DISPATCHED); 
        setContentView(R.layout.main);
       
        onebutton = (Button)findViewById(R.id.onebutton);
        onebutton.setOnClickListener(new Mybutton());
    }
 
    class Mybutton implements OnClickListener{
  @Override
  public void onClick(View v) {
   if(kaiguan){

    onebutton.setBackgroundResource(R.drawable.bgon);
    camera = Camera.open(); 
    parameters = camera.getParameters();
    parameters.setFlashMode(Parameters.FLASH_MODE_TORCH);
    camera.setParameters(parameters);
    kaiguan = false;
   }else{
    onebutton.setBackgroundResource(R.drawable.bg);
    parameters.setFlashMode(Parameters.FLASH_MODE_OFF);
    camera.setParameters(parameters);
    kaiguan = true;
    camera.release();
   }
  }
    }

 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  if(keyCode == KeyEvent.KEYCODE_BACK){
   back++;
   switch (back) {
   case 1:
    Toast.makeText(FlashLightActivity.this,R.string.press_again_to_exit,Toast.LENGTH_LONG).show();
    break;
   case 2:
    back = 0;//初始化back值
    Myback();
    break;
   }
   return true;//设置成false让back失效    ，true表示 不失效
  }else if(keyCode == KeyEvent.KEYCODE_HOME)
  {
   Myback();
   return super.onKeyDown(keyCode, event);
  }
  else{
   return super.onKeyDown(keyCode, event);
  }
 }
 
 public void Myback(){ //关闭程序
   if(kaiguan){//开关关闭时
    FlashLightActivity.this.finish();
    android.os.Process.killProcess(android.os.Process.myPid());//关闭进程
   }else if(!kaiguan){//开关打开时
    camera.release();
    FlashLightActivity.this.finish();
    android.os.Process.killProcess(android.os.Process.myPid());//关闭进程
    kaiguan = true;//避免，打开开关后退出程序，再次进入不打开开关直接退出时，程序错误
   }
 }
}