Android中“再按一次返回键退出程序”实现

    private long exitTime = 0; 

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){
    if((System.currentTimeMillis()-exitTime) > 2000){
    Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
    exitTime = System.currentTimeMillis();
    } else {
    finish();
    System.exit(0);
    }
    return true;
    }
    return super.onKeyDown(keyCode, event);
    }