回退键功能

    // 设置回退建功能
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            exit();
            return false;
        } else {
            return super.onKeyDown(keyCode, event);
        }
    }
    public void exit(){
        if (!isExit) {
            isExit = true;
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
            mHandler1.sendEmptyMessageDelayed(0, 2000);
        } else {
            Intent intent = new Intent(Intent.ACTION_MAIN);
            intent.addCategory(Intent.CATEGORY_HOME);
            startActivity(intent);
            System.exit(0);
        }
    }
    Handler mHandler1 = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            isExit = false;
        }

    };
    //回退建功能结束