Question

-[__NSArrayM objectAtIndex:]: index 6 beyond bounds [0 .. 4]'我有点问题如何显示(null)如果我没有数据。

这是代码

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{

if ([[bookList objectAtIndex:indexPath.item]quiz_url]==[[bookList objectAtIndex:6]quiz_url]) {// This one is problem, I have  `objectAtIndex:` only 0 - 5 .

//             quiz_all = [[bookList objectAtIndex:indexPath.item]quiz_url];
        _getQuiz6 = [[bookList objectAtIndex:6]quiz_url];
         NSLog(@" test quiz6 = %@",_getQuiz6); //It's possible? Can I print `(null)` if no data.
    }
...

和

-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return [bookList count];
}

我在webservice上没有数据[[bookList objectAtIndex:6]quiz_url]。

Answer 1

你有很多方法可以解决这个问题。处理它的一种方法是使用“占位符”对象填充内容，例如NSNull。或者您可以修改Book对象并添加isLoaded等属性。

无论你选择哪种方法，然后（坚持使用NSNull）;

- (UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    // Whatever code you have

    Book *book = [bookList objectAtIndex:indexPath.item];

    // NSNull is a singleton, you can safely do pointer comparison
    if (book == [NSNull null])
    {
        // Show loading or something in the cell
        cell.loadingOrSomething = YES;

        // Return the cell here
        return cell;
    }

    // book wasn't NSNull, then proceed with the rest of stuff
    NSURL *url = [book quiz_url];

    cell.loadingOrSomething = NO;

    return cell;
}

Answer 2

如果需要，您可以使用类别。标题中的某处包括：

@interface NSArray (custom)
-(id)quizURLAtIndex:(int)index;
@end

并在.m文件中添加：

@implementation NSArray (custom)

-(id)quizURLAtIndex:(int)index{
    if(index >= self.count) return nil;
    else return [[self objectAtIndex:index] quiz_url];
}

@end

从现在开始，无论何时，您都可以拨打[bookList quizURLAtIndex:indexPath.item]而不是[[bookList objectAtIndex:indexPath.row] quiz_url]

- [__ NSArrayM objectAtIndex：]问题

2 个答案: