iOS - 应用程序崩溃是 Garbagecollector 的错吗？

Question

我和我的团队正在开发一个测验应用程序，我们有 1 个 View ，我们只需重新加载标签和按钮上的文本。现在当我们开始测验时，有 2 个循环从数据库加载问题和答案。在这些循环中，我们初始化在 .h 文件中声明的对象。所以我们做的是:obj = [[class alloc] initwith:stuff];在我们第 6 次调用 2 个循环所在的方法之前，它一直运行良好。有时它在第一个循环中崩溃，有时在第二个循环中崩溃。现在奇怪的是，如果我们在“再次播放”按钮上调用该方法两次，它会在第 3 次崩溃(方法调用 6 次然后 = 崩溃)，所以我们认为它与内存或所以。我们尝试清理项目，在 iPad 和模拟器上运行它。没有效果。错误消息是我们在第一个循环中填充的数组在第二个循环中为空。

目前我无法为您提供代码片段，但最简单的方法是在用户按下“再次播放”按钮时简单地重置应用程序。有什么简单的方法可以做到这一点？如果应用程序只是关闭并重新打开启动画面，那也很好。

如果你现在不能提出任何建议，我明天会添加代码片段

提前致谢

编辑:SIGABRT这是错误消息:SoccerQuiz[1563:f803] * 由于未捕获的异常“NSRangeException”而终止应用程序，原因:“* -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'* 首先抛出调用栈:(0x159e022 0x172fcd6 0x158ad88 0x4719 0x3455 0x159fe99 0xe214e 0xe20e6 0x188ade 0x188fa7 0x188266 0x1073c0 0x1075e6 0xeddc4 0xe1 634 0x1488ef5 0x1572195 0x14d6ff2 0x14d58da 0x14d4d84 0x14d4c9b 0x14877d8 0x148788a 0xdf626 0x20ed 0x2055)终止调用抛出异常(lldb)

我的代码:

-(NSMutableArray*) readFromDatabase{

//if modus is true 20 questions will be loaded(untested). we set mds to 10 for now which works for the first 5 times and then crashes the 6th time
int mds = 0;
if (modus)
 mds = 20;
 else mds = 10;
bool loop = true;

//a_data is the array in which the data object is. it is filled with the questions and answeres    
NSMutableArray * a_data = [[NSMutableArray alloc] init];
//check_id is the array in which the question ids from the database are saved
NSMutableArray * check_id = [[NSMutableArray alloc] init];


//ant is the array in which the 4 possible answers are saved.
NSMutableArray *ant = [[NSMutableArray alloc] init];

//in id_frage the id of the question is saved and in frage the question itself
NSString *id_frage = [[NSString alloc] init];
NSString *frage = [[NSString alloc] init];

//in sql_id the statement for the question is saved
NSString *sql_id = [[NSString alloc] initWithFormat:@"select id from QQUESTION where level = %@ order by random() limit 1", difficulty];

//in the method sqlquery we get data from the database
id_frage = [[self sqlquery: sql_id with:@"Q"] objectAtIndex:0];

[check_id addObject:id_frage];


NSLog(@"1");
//we use these loops to read unique question ids from the database, as you can see random questions are loaded from the database (sql_id statement)
for (int z = 0; z < mds; z++)
{
    while (loop)
    {
    for (int y = 0; y <= check_id.count; y++)
    {
        //this loop checks if the question id is already in check_id
        if ([[check_id objectAtIndex:y] isEqualToString:id_frage])
        {
            id_frage = [[self sqlquery: sql_id with:@"Q"] objectAtIndex:0];    

            break;

        }
        else { 
            //if the id doesnt already exit, it will be added to the check_id array
            if (y == check_id.count-1)
            {
            [check_id addObject:id_frage];
            loop = false;
            break; 
            }
        }
    }
    }
    loop = true;
    id_frage = [[self sqlquery: sql_id with:@"Q"] objectAtIndex:0];
}

      NSLog(@"2");




//this loops loads the questions and answers that fit to the question ids
for (int x = 0; x < mds; x++)
{


//sql_q statement for the questions
NSString *sql_q = [[NSString alloc] initWithFormat:@"select TEXT from QQUESTIONTEXT where ID_QUESTION = '%@' and LANGUAGE = '%@'", [check_id objectAtIndex:x], language];

frage = [[self sqlquery:sql_q with:@"Q" ]objectAtIndex:0];

//sql_a statement for the answers    
NSString *sql_a = [[NSString alloc] initWithFormat:@"select answer.correct, answertext.text from QANSWER as answer, QANSWERTEXT as answertext where answer.ID_QUESTION='%@' and answer.ID = answertext.ID_ANSWER and answertext.LANGUAGE = '%@'", [check_id objectAtIndex:x], language];

ant = [self sqlquery: sql_a with:@"A"];    

    //this loop sets the right answer at the first position of the array
    for(int a = 0; a<ant.count-1; a++)
    {
        if([[ant objectAtIndex:a] isEqualToString:@"1"])
        {
            a++;
            NSString *h = [[NSString alloc]initWithFormat:[ant objectAtIndex:1]];

            [ant replaceObjectAtIndex:1 withObject:[ant objectAtIndex:a]];
            [ant replaceObjectAtIndex:a withObject:h];
            a--;

            break;

        }

    }

//this data object 'd' is filled with a question and 4 answers and 10 or 20 will be added to a_data which will be returned
d = [[data alloc] initFrage:frage mitAntwort1:[ant objectAtIndex:1] Antwort2:[ant objectAtIndex:3] Antwort3:[ant objectAtIndex:5] Antwort4:[ant objectAtIndex:7]];
[a_data addObject:d];
}

 NSLog(@"3");




return a_data;

Answer 1

iOS 上没有垃圾收集器——有手动或自动引用计数 (ARC)。在任何一种情况下，对象都是通过使用保留和释放来进行引用计数的。使用 ARC，您不必自己进行这些调用，但这并不意味着您仍然不会遇到问题。

没有您的代码或任何信息，我只能提供一般性建议。我假设您的崩溃是 EXC_BAD_ACCESS 或类似的东西。

我写了一篇博客来解释这个问题以及如何解决它

http://loufranco.com/blog/files/Understanding-EXC_BAD_ACCESS.html

在你的情况下，这就是我会做的

1. 运行分析并修复它标记的每个问题
2. 打开僵尸并重现您的问题。如果您正在与僵尸对象交谈，现在应该更容易看到发生了什么。

如果失败，则打开 Debug Malloc 并使用我博客中链接的工具来调试问题。

根据问题编辑进行编辑:

您遇到异常——在您提供的代码中，有几个 objectAtIndex 调用——使用此处的说明在异常上创建断点:

http://www.dosomethinghere.com/2011/04/18/xcode-4-exception-breakpoint/

并告诉我们确切的路线。

基本上，您不能在空数组上使用 0 调用 objectAtIndex - 因此您需要先检查长度。