Android/Java：检查 arraylist 是否为空，然后启动另一个活动
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Android/Java: Check if arraylist is empty and then launch another activity
提问by psalomonsen
Im trying to build this Quiz program where a person is asked a question from and then has to answer, it's a game for two persons, and they just go through all the questions and the game ends.
我试图建立这个测验程序，一个人被问到一个问题，然后必须回答，这是一个两个人的游戏，他们只是通过所有的问题，游戏就结束了。
What i've managed to make so far is the general code for loading the array (the array in the strings.xml file) into an arraylist and then take a random id from 0 to arraylist.size and then show that string (Questions) then it deletes the random id and takes a new one.
到目前为止，我设法制作的是将数组（strings.xml 文件中的数组）加载到数组列表中的通用代码，然后从 0 到 arraylist.size 取一个随机 id，然后显示该字符串（问题）然后它删除随机 id 并获取一个新的。
But when ive run through all the id's in the arraylist the program crashes, my code looks like this: http://pastebin.com/MaEj49BL
但是当我遍历 arraylist 中的所有 id 时，程序崩溃了，我的代码如下所示：http: //pastebin.com/MaEj49BL
The important part is this:
重要的部分是这样的：
public void gameCode()
{
setContentView(R.layout.game);
if (mList == null)
{
String[] mQuestions = getResources().getStringArray(R.array.mQuestions);
mList = new ArrayList();
Collections.addAll(mList, mQuestions);
}
else if (mList.isEmpty())
{
m = (TextView)findViewById(R.id.textView1);
m.setText("You've run out of questions!");
}
if (wList == null)
{
String[] wQuestions = getResources().getStringArray(R.array.wQuestions);
wList = new ArrayList();
Collections.addAll(wList, wQuestions);
}
else if (wList.isEmpty())
{
w = (TextView)findViewById(R.id.textView1);
w.setText("You've run out of questions!");
}
//Takes a random ID from the arraylist
int rndm = generator.nextInt(mList.size());
int rndw = generator.nextInt(wList.size());
//Sets the Strings to a random number from one of the array lists
String qMan = (String) mList.get(rndm);
String qWoman = (String) wList.get(rndw);
if(i == 0)
{
//Defines that w is textView1 with the value of qWoman
w = (TextView)findViewById(R.id.textView1);
w.setText(qWoman);
wList.remove(rndw);
i = 1;
final Button buttonNext = (Button) findViewById(R.id.buttonNext);
buttonNext.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
gameCode();
}
});
}
else
{
m = (TextView)findViewById(R.id.textView1);
m.setText(qMan);
mList.remove(rndm);
i = 0;
final Button buttonNext = (Button) findViewById(R.id.buttonNext);
buttonNext.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
gameCode();
}
});
}
}
}
}
There is comments in the source code from the pastebin. Right now I just need to to change the text to "You've run out of questions"
pastebin 的源代码中有注释。现在我只需要将文本更改为“你的问题已经用完了”
回答by Chris
You're checking whether or not the 2 arrays are empty but you're not short-circuiting the remainder of the logic when they are...
您正在检查 2 个数组是否为空，但是当它们为空时，您并没有短路其余的逻辑...
if mList and wList are empty, you should bypass the remainder of the method or, at a minimum, check that mList.size() > 0and wList.size()>0before trying to get the next random question from each array.
如果 mList 和 wList 为空，您应该绕过该方法的其余部分，或者至少mList.size() > 0and wList.size()>0在尝试从每个数组中获取下一个随机问题之前进行检查。
回答by anirudh bhatnagar
Use CollectionUtils.isEmpty() which is null safe
使用 CollectionUtils.isEmpty() 是空安全的
