按两次back键返回

Java代码

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);???

}????