Android 完全退出应用程序的解决方法

public class ExitUtil {
 public static final int EXIT_APPLICATION = 0x0001;
 private Context mContext;
 public ExitUtil(Context context) {
  mContext = context;
 }
 // 完全退出应用程序
 public void exit() {
  Intent intent = new Intent(mContext, MainActivity.class);
  // 设置FLAG!!!表示从当前Activity跳转到intent构造方法中添加的类，并且把两个Activity之间的Activity给finish掉！
  intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
  // 发出退出应用程序指示
  intent.putExtra("flag", EXIT_APPLICATION);
  mContext.startActivity(intent);
 }
}

public class BActivity extends Activity {
 private static final int MENU_EXITAPPLICATION = Menu.FIRST;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  TextView tv = new TextView(this);
  tv.setText("wecolme!");
  setContentView(tv);
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  menu.add(0, MENU_EXITAPPLICATION, 0, "退出程序");
  return super.onCreateOptionsMenu(menu);
 }
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  // 其它Activity调用程序就通过此方法
  if (item.getItemId() == MENU_EXITAPPLICATION) {
   ExitUtil eu = new ExitUtil(this);
   eu.exit();
  }
  return super.onOptionsItemSelected(item);
 }
}

public class MainActivity extends Activity {
 Button btn = null;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  btn = (Button) findViewById(R.id.btn);
  btn.setOnClickListener(new OnClickListener() {// 点击进入BActivity
   @Override
   public void onClick(View v) {
    Intent intent = new Intent(getApplicationContext(), BActivity.class);
    startActivity(intent);
   }
  });
 }
 // 接受退出程序的指令
 @Override
 protected void onStart() {
  int flag = getIntent().getIntExtra("flag", 0);// 第一次,进入应用时获取得到的flag为默认的值0!
  if (flag == ExitUtil.EXIT_APPLICATION) {
   finish();
  }
  Log.i("TAG", "Start");
  super.onStart();
 }
 // 当Activity是单例模式的时候，两次启动该Activity就不会调用onCreate->onStart这些方法了
 @Override
 protected void onNewIntent(Intent intent) {
  int flag = getIntent().getIntExtra("flag", 0);
  if (flag == ExitUtil.EXIT_APPLICATION) {
   finish();
  }
  Log.i("TAG", "NewIntent");
  super.onNewIntent(intent);
 }
}