Question

我在洗牌数组中找到的所有示例都是针对NSMutableArrays的。将NSArray复制到NSMutable数组，混洗，然后复制总是会使应用程序崩溃。是否有可能改组NSArray？

Objective-c中的任何内容类似于Collections.shuffle（）（Java）？

修改

static NSUInteger random_below(NSUInteger n) {
NSUInteger m = 1;

do {
    m <<= 1;
} while(m < n);

NSUInteger ret;

do {
    ret = random() % m;
} while(ret >= n);

return ret;
}
- (NSArray *)loadAllData{
    XYZAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;
    NSFetchRequest *request = [[NSFetchRequest alloc] init]; 
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Quote" inManagedObjectContext:managedObjectContext]; 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"id" ascending:YES];  
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];   

    [request setSortDescriptors:sortDescriptors];
    [request setEntity: entity]; 

    NSError *myError;   
    NSArray *theResults = [managedObjectContext executeFetchRequest:request error:&myError];

    if (theResults == nil) {
        NSLog(@"Testing: No results found");
    }else {
        NSLog(@"Testing: Results found.");
    }

    [request release];
    [sortDescriptors release];

    for(NSUInteger i = [theResults count]; i > 1; i--) {
        NSUInteger j = random_below(i);
        [theResults exchangeObjectAtIndex:i-1 withObjectAtIndex:j];
    }

    return theResults;
}




warning: 'NSArray' may not respond to '-exchangeObjectAtIndex:withObjectAtIndex:' which crashed the application.     

error: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[_PFArray exchangeObjectAtIndex:withObjectAtIndex:]: unrecognized selector sent to instance 0x3d35a40

Answer 1

行。我想我看到了一个问题。始终查看错误消息。我以为你说你在这个函数中使用了NSMutableArrays？

NSArray *theResults = [managedObjectContext executeFetchRequest:request error:&myError];

将其更改为

NSMutableArray *theResults = [[managedObjectContext executeFetchRequest:request error:&myError] mutableCopy];

告诉我它是否有效，如果没有，我会尽力帮助。

更多信息：

-exchangeObjectAtIndex:withObjectAtIndex:

是NSMutableArray的方法。您使用的是NSArray，它们是不同的类（NSMutableArray是NSArray的子类（并添加了可以修改它的方法））。

我如何改变NSArray？

修改

1 个答案: