双击退出Activity

利用时间差来实现：

private long exitTime = 0;
public void ExitApp(){
if ((System.currentTimeMillis() - exitTime) > 2000){
Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
exitTime = System.currentTimeMillis();
} else{
finish();
}
}
public boolean onKeyDown(int keyCode, KeyEvent event) {

if (keyCode == KeyEvent.KEYCODE_BACK) {
ExitApp();
return true;
}
return super.onKeyDown(keyCode, event);
}
}