iphone - 从文件读取数据时出现“NSRangeException”

Question

我试图在按下主页按钮时保存数据。这是我的相关代码。

   - (NSString *) saveFilePath
{
    NSArray *path =
    NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    return [[path objectAtIndex:0] stringByAppendingPathComponent:@"savefile.plist"];

}
- (void)applicationDidEnterBackground:(UIApplication *)application {
     NSArray *values = [[NSArray alloc] initWithObjects:
                   [NSNumber numberWithInt:askedQuestions],  //for questionLabel
                   [NSNumber numberWithInt:timeMin],         //timeMin
                   [NSNumber numberWithInt:timeSec],         //timeSec
                   [NSNumber numberWithInt:skipCount],       //skipped question
                   [NSNumber numberWithInt:correctAnswers],   //corectAnswers
                   nil];
[values writeToFile:[self saveFilePath] atomically:YES];
 }

saveFilePath 方法提供文件路径。

并在viewDidLoad中

NSString *myPath = [self saveFilePath];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:myPath]; 
if (fileExists)
{
    NSArray *values = [[NSArray alloc] initWithContentsOfFile:myPath];
    _readerLabel.text = [[values objectAtIndex:0] stringValue];
    askedQuestions=[[values objectAtIndex:0] intValue];
    timeMin=[[values objectAtIndex:1]intValue];
    timeSec=[[values objectAtIndex:2]intValue];
    skipCount=[[values objectAtIndex:3]intValue];
    correctAnswers=[[values objectAtIndex:4]intValue];

}

UIApplication *myApp = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(applicationDidEnterBackground:)
 name:UIApplicationDidEnterBackgroundNotification
 object:myApp];

我得到了这个:

Terminating app due to uncaught exception 'NSRangeException', reason: '-[__NSCFArray objectAtIndex:]:        index (0) beyond bounds (0)'
*** First throw call stack:
(0x16a1012 0x13aee7e 0x16a0deb 0x16957e0 0x6891 0x312d 0x305817 0x305882 0x254a25 0x254dbf 0x254f55     0x25df67 0x221fcc 0x222fab 0x234315 0x23524b 0x226cf8 0x2703df9 0x2703ad0 0x1616bf5 0x1616962 0x1647bb6   0x1646f44 0x1646e1b 0x2227da 0x22465c 0x26cd 0x25f5)
libc++abi.dylib: terminate called throwing an exception

代码哪里出了问题。请帮忙!

Answer 1

您没有检查是否有任何效果!

如果会发生什么

NSArray *values = [[NSArray alloc] initWithContentsOfFile:myPath];

要么失败(文件可能不存在)，要么返回一个包含 0 个项目的数组？

您需要添加类似以下内容:

NSArray *values = [[NSArray alloc] initWithContentsOfFile:myPath];
if (values.count > 0) {
  ...
}

您还应该在 applicationDidEnterBackground: 上设置一个断点，并逐步执行以确保您的保存方法按预期工作。

<小时/>

另外，我怀疑这两行之一是错误的:

_readerLabel.text = [[values objectAtIndex:0] stringValue];
askedQuestions=[[values objectAtIndex:0] intValue];

他们都在请求索引 0 处的项目