Android-发送广播结束所有Activity

public class BaseActivity extends Activity {  
    @Override  
	protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState);  
       //注册广播
        IntentFilter filter = new IntentFilter();  
        filter.addAction("com.lioil.win.close");  
        registerReceiver(new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                //注销广播
                unregisterReceiver(this); 
                ((Activity) context).finish();
            }
       }, filter);  
    }
  
    public void close() {
        //发送广播
       Intent intent = new Intent();
       intent.setAction("com.lioil.win.close");
       sendBroadcast(intent);
       finish();
    }
} 

Public class MyActivity extends BaseActivity {
    @Override  
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.a1);
    } 
    private long exitTime = 0;

    @Override  
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode == KeyEvent.KEYCODE_BACK){
            //时间间隔大于2秒不退出
            if((System.currentTimeMillis()-exitTime) > 2000){
                Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();  
                exitTime = System.currentTimeMillis();  
            } else {
                //使用基类BaseActivity方法,发送广播给所有Activity，退出应用
                close();  
            }
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }
}