一次关闭所有Activity和连续点击两次返回键关闭程序的方法

package net.loonggg.test;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
public class BaseActivity extends Activity {
 /**
  * 关闭Activity的广播，放在自定义的基类中，让其他的Activity继承这个Activity就行
  */
 protected BroadcastReceiver finishAppReceiver = new BroadcastReceiver() {
 @Override
 public void onReceive(Context context, Intent intent) {
 finish();
 }
 };
 @Override
 public void onResume() {
 super.onResume();
 // 在当前的activity中注册广播
 IntentFilter filter = new IntentFilter();
 filter.addAction("net.loonggg.exitapp");
 this.registerReceiver(this.finishAppReceiver, filter);
 }
 @Override
 protected void onDestroy() {
 super.onDestroy();
 this.unregisterReceiver(this.finishAppReceiver);
 }
}

/**
  * 记录标记时间
  */
 private long exitTime = 0;
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
 if (KeyEvent.KEYCODE_BACK == keyCode) {
 // 判断是否在两秒之内连续点击返回键，是则退出，否则不退出
 if (System.currentTimeMillis() - exitTime > 2000) {
 Toast.makeText(getApplicationContext(), "再按一次退出程序",
 Toast.LENGTH_SHORT).show();
 // 将系统当前的时间赋值给exitTime
 exitTime = System.currentTimeMillis();
 } else {
 exitApp();
 }
 return true;
 }
 return super.onKeyDown(keyCode, event);
 }

/** 
     * 退出应用程序的方法，发送退出程序的广播 
     */  
    private void exitApp() {  
        Intent intent = new Intent();  
        intent.setAction("net.loonggg.exitapp");  
        this.sendBroadcast(intent);  
    }