Android_Back键再按一次退出程序

主要思路：在Activity中覆写Activity的onKeyDown方法

    private long exitTime = 0;
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            if ((System.currentTimeMillis() - exitTime) > 2000) {
                Toast.makeText(this,getResources().getString(R.string.tips_exit),0).show();;
                exitTime = System.currentTimeMillis();
            } else {
                Intent intent = new Intent(Intent.ACTION_MAIN);
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                intent.addCategory(Intent.CATEGORY_HOME);
                startActivity(intent);
            }
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }