iOS:UITableViewController——cellForRowAtIndexPath 单元格创建

Question

我知道 Apple 文档没有指定 cellForRowAtIndexPath 按顺序进行，即首先它会转到第 0 节，索引 0；然后是第 0 节，索引 2；然后是第 1 节，索引 0...等等。我认为它跳来跳去。

有什么更好的方法来完成下面的工作？目前我不断收到错误

NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 3 beyond bounds [0 .. 2]'

错误出现 b/c 我认为 cellForRowAtIndexPath 跳转并标记*sectioned = NULL，因此条件被跳过，它进入一个空数组或由于进入错误条件而超过索引计数。

代码如下:

... declared and synthesized 
NSManaged *object;
@property (strong, nonatomic) NSNumber *sevenDaysSectionFilled;
@property (strong, nonatomic) NSNumber *fourteenDaysSectionFilled;
@property (strong, nonatomic) NSNumber *thirtyDaysSectionFilled;


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    object = NULL;
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    if (indexPath.section == 0)
    {
        if ((SevenDaysArraySectioned == [NSNumber numberWithBool:YES]) && (sevenDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
            object = [pastSevenDayArray objectAtIndex:indexPath.row];
            sevenDaysSectionFilled = [NSNumber numberWithBool:YES];
        }

        else if ((fourteenDaysArraySectioned == [NSNumber numberWithBool:YES]) && (fourteenDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
            object = [pastFourteenDaysArray objectAtIndex:indexPath.row];
            fourteenDaysSectionFilled = [NSNumber numberWithBool:YES];
        }

        else if ((thirtyDaysArraySectioned == [NSNumber numberWithBool:YES]) && (thirtyDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
            object = [pastThirtyDaysArray objectAtIndex:indexPath.row];
            thirtyDaysSectionFilled = [NSNumber numberWithBool:YES];
        }

    else if (indexPath.section == 1)
    {
        if ((fourteenDaysArraySectioned == [NSNumber numberWithBool:YES]) && (fourteenDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
            object = [pastFourteenDaysArray objectAtIndex:indexPath.row];
            fourteenDaysSectionFilled = [NSNumber numberWithBool:YES];
        }

        else if ((thirtyDaysArraySectioned == [NSNumber numberWithBool:YES]) && (thirtyDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
            object = [pastThirtyDaysArray objectAtIndex:indexPath.row];
            thirtyDaysSectionFilled = [NSNumber numberWithBool:YES];
        }

    else if (indexPath.section == 2)
    {
        if ((thirtyDaysArraySectioned == [NSNumber numberWithBool:YES]) && (thirtyDaysSectionFilled != [NSNumber numberWithBool:YES]))
        {
             object = [pastThirtyDaysArray objectAtIndex:indexPath.row];
            thirtyDaysSectionFilled = [NSNumber numberWithBool:YES];
        }
     }

NSString *entityName = [[object entity]name];
cell.textLabel.text = [NSString stringWithFormat:@"%@   %i", entityName, [indexPath row]];

  object = NULL;
  return cell;
}

请告诉我是否有更好的方法来完成此操作。谢谢。

*编辑

这有点复杂，但在这里:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    numberOfSections = 0;

    if ([pastSevenDayArray count] > 0) numberOfSections++;
    if ([pastFourteenDaysArray count] > 0) numberOfSections++;
    if ([pastThirtyDaysArray count] > 0) numberOfSections++;
    if ([pastSixtyDaysArray count] > 0) numberOfSections++;
    if ([pastNinteyDaysArray count] > 0) numberOfSections++;
    if ([pastArray count] > 0) numberOfSections++;

    [self numberOfCells];


    return numberOfSections;
}

细胞数

-(void)numberOfCells
{
    for (int section = 0; section<numberOfSections; section ++)
    {
        if (section == 0)
        {
            if ([pastSevenDayArray count] > 0)
            {
                SevenDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastSevenDayArray count];
                sectionZeroHeader = sevenDaysSectionLabel;
            }
            else if ([pastFourteenDaysArray count] > 0)
            {
                fourteenDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastFourteenDaysArray count];
                sectionZeroHeader = fourteenDaysSectionLabel;
            }
            else if ([pastThirtyDaysArray count] > 0)
            {
                thirtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastThirtyDaysArray count];
                sectionZeroHeader = thirtyDaysSectionLabel;
            }
            else if ([pastSixtyDaysArray count] > 0)
            {
                sixtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastSixtyDaysArray count];
                sectionZeroHeader = sixtyDaysSectionLabel;

            }
            else if ([pastNinteyDaysArray count] > 0)
            {
                ninetyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastNinteyDaysArray count];
                sectionZeroHeader = ninetyDaysSectionLabel;
            }
            else if ([pastArray count] > 0)
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionZeroCellCount = [pastArray count];
                sectionZeroHeader = pastSectionLabel;
            }
        }

        else if (section == 1)
        {    
            if (([pastFourteenDaysArray count] > 0) && (fourteenDaysArraySectioned != [NSNumber numberWithBool:YES]))

            {
                fourteenDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionOneCellCount = [pastFourteenDaysArray count];
                sectionOneHeader = fourteenDaysSectionLabel;
            }
            else if (([pastThirtyDaysArray count] > 0) && (thirtyDaysArraySectioned != [NSNumber numberWithBool:YES]))

            {
                thirtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionOneCellCount = [pastThirtyDaysArray count];
                sectionOneHeader = thirtyDaysSectionLabel;
            }
            else if (([pastSixtyDaysArray count] > 0) && (sixtyDaysArraySectioned != [NSNumber numberWithBool:YES]))
            {
                sixtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionOneCellCount = [pastSixtyDaysArray count];
                sectionOneHeader = sixtyDaysSectionLabel;
            }
            else if (([pastNinteyDaysArray count] > 0) && (ninetyDaysArraySectioned != [NSNumber numberWithBool:YES]))

            {
                ninetyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionOneCellCount = [pastNinteyDaysArray count];
                sectionOneHeader = ninetyDaysSectionLabel;
            }
            else if (([pastArray count] > 0) && (pastArraySectioned != [NSNumber numberWithBool:YES]))
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionOneCellCount = [pastArray count];
                sectionOneHeader = pastSectionLabel;
            }
        }
        else if (section ==2)
        {
            if (([pastThirtyDaysArray count] > 0) && (thirtyDaysArraySectioned != [NSNumber numberWithBool:YES]))

            {
                thirtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionTwoCellCount = [pastThirtyDaysArray count];
                sectionTwoHeader = thirtyDaysSectionLabel;
            }
            else if (([pastSixtyDaysArray count] > 0) && (sixtyDaysArraySectioned != [NSNumber numberWithBool:YES]))
            {
                sixtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionTwoCellCount = [pastSixtyDaysArray count];
                sectionTwoHeader = sixtyDaysSectionLabel;
            }
            else if (([pastNinteyDaysArray count] > 0) && (ninetyDaysArraySectioned != [NSNumber numberWithBool:YES]))

            {
                ninetyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionTwoCellCount = [pastNinteyDaysArray count];
                sectionTwoHeader = ninetyDaysSectionLabel;
            }
            else if (([pastArray count] > 0) && (pastArraySectioned != [NSNumber numberWithBool:YES]))
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionTwoCellCount = [pastArray count];
                sectionTwoHeader = pastSectionLabel;
            }
        }
        else if (section ==3)

        {
            NSLog(@"Entered Section %i", section);

            if (([pastSixtyDaysArray count] > 0) && (sixtyDaysArraySectioned != [NSNumber numberWithBool:YES]))            {
                sixtyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionThreeCellCount = [pastSixtyDaysArray count];
                sectionThreeHeader = sixtyDaysSectionLabel;
            }
            else if (([pastNinteyDaysArray count] > 0) && (ninetyDaysArraySectioned != [NSNumber numberWithBool:YES]))
            {
                ninetyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionThreeCellCount = [pastNinteyDaysArray count];
                sectionThreeHeader = ninetyDaysSectionLabel;          
            }
            else if (([pastArray count] > 0) && (pastArraySectioned != [NSNumber numberWithBool:YES]))
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionThreeCellCount = [pastArray count];
                sectionThreeHeader = pastSectionLabel;
            }
        }
        else if (section ==4)
        {
            NSLog(@"Entered Section %i", section);

            if (([pastNinteyDaysArray count] > 0) && (ninetyDaysArraySectioned != [NSNumber numberWithBool:YES]))
            {
                ninetyDaysArraySectioned = [NSNumber numberWithBool:YES];
                sectionFourCellCount = [pastNinteyDaysArray count];
                sectionFourHeader = ninetyDaysSectionLabel;
            }
            else if (([pastArray count] > 0) && (pastArraySectioned != [NSNumber numberWithBool:YES]))
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionFourCellCount = [pastArray count];
                sectionFourHeader = pastSectionLabel;
            }
        }

        else if (section ==5)
        {
            NSLog(@"Entered Section %i", section);

            if (([pastArray count] > 0) && (pastArraySectioned != [NSNumber numberWithBool:YES]))
            {
                pastArraySectioned = [NSNumber numberWithBool:YES];
                sectionFiveCellCount = [pastArray count];
                sectionFiveHeader = pastSectionLabel;
            }
        }

    }

}

节中的行数

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

    if (section == 0)
    {
        return sectionZeroCellCount;
    }

    else if (section == 1)
    {
        return sectionOneCellCount;
    }
    else if (section == 2)
    {
        return sectionTwoCellCount;
    }
    else if (section == 3)
    {
        return sectionThreeCellCount;
    }
    else if (section == 4)
    {
        return sectionFourCellCount;
    }
    if (section == 5)
    {
        return sectionFiveCellCount;
    }
}

编辑 2

标题:

- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
    return 30.0;
}

- (UIView *) tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    UIView *headerView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 150)];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 3, tableView.bounds.size.width - 10, 25)];
    label.backgroundColor = [UIColor clearColor];
    [label setFont:[UIFont boldSystemFontOfSize:16]];
    label.textColor = [UIColor whiteColor];

    if (section == 0)
    {
        label.text = sectionZeroHeader;
    }
    else if (section == 1)
    {
        label.text = sectionOneHeader;
    }

    else if (section == 2)
    {
        label.text = sectionTwoHeader;
    }
    else if (section == 3)
    {
        label.text = sectionThreeHeader;
    }
    else if (section == 4)
    {
        label.text = sectionFourHeader;
    }
    else if (section == 5)
    {
        label.text = sectionFiveHeader;
    }    

    [headerView addSubview:label];
    return headerView;
}

Answer 1

在各种实例变量中维护了很多不必要的状态。我们可以使用集合和其他数据结构来构建表格的定义，然后在我们的数据源/委托(delegate)方法中引用它。

这个 View Controller 的基本思想是，每个部分都由一个 CVSectionModel 对象表示，该对象包含该部分的行数据，以及特定于部分的信息，例如标题 View 。在 viewDidLoad 中，我们构建了这些部分模型，并且每当我们完成数据更新时，我们都应该重新构建它们。要尝试不同的数据安排，请将 viewDidLoad 中对 testCase1 的调用替换为其他测试方法之一。

我们维护了一系列的部分模型，并且只有在有内容要显示的情况下才会为部分创建模型。如您所见，这简化了从哪个数组中获取行信息以及每个部分中有多少行的计算。我们只是询问段模型要做什么，而不是同步几个不同的实例变量。

请注意，此表 Controller 不支持更精细的内容插入、删除或重新排序动画，因此如果需要，则需要额外的工作。不过，它确实支持在更新后定期重新加载表，正如在 viewDidLoad 后运行 10 秒的 block 中所见。

请检查代码并提出任何问题。这是实现文件，但 header 中除了 @interface CVViewController: UIViewController @end 什么都没有。

@interface CVSectionModel : NSObject

@property (nonatomic) NSArray *rowModels;
@property (nonatomic) NSString *sectionTitle;
@property (nonatomic) NSInteger tag; // possibly useful for animations, different behavior on section, etc.

@end

@implementation CVSectionModel

@end


@interface CVViewController () <UITableViewDataSource, UITableViewDelegate>

@property (weak, nonatomic) IBOutlet UITableView *tableView;

@property (nonatomic) NSArray *sectionModels;

@property (nonatomic) NSArray *sevenDays;
@property (nonatomic) NSArray *fourteenDays;
@property (nonatomic) NSArray *thirtyDays;

@end

@implementation CVViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    // In your application, you'll be loading and processing your real data
    // But here I'm just going to simulate a number of cases with strings for illustration
    // Call the other methods to try different configurations
    [self testCase1];

    // We call this once on viewDidLoad. You'll also want to call it whenever you update the underlying data, as in the block below
    [self processSectionData];

    [self.tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:@"IDENTIFIER"];

    // Demonstrate support for modifying the underlying data and refresh the view.
    // Uncomment to test it.
//    double delayInSeconds = 10.0;
//    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
//    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
//        [self testCase2];
//        [self processSectionData];
//        [self.tableView reloadData];
//    });
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [self.sectionModels count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [((CVSectionModel *)self.sectionModels[section]).rowModels count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"IDENTIFIER"];
    // In your app this appears to be an NSManagedObject of some type, here it's just a string
    NSString *modelForRow = ((CVSectionModel *)self.sectionModels[indexPath.section]).rowModels[indexPath.row];
    cell.textLabel.text = modelForRow;
    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
    return 30.0;
}

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    NSString *sectionTitle = ((CVSectionModel *)self.sectionModels[section]).sectionTitle;
    UIView *headerView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 150)];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 3, tableView.bounds.size.width - 10, 25)];
    label.backgroundColor = [UIColor clearColor];
    [label setFont:[UIFont boldSystemFontOfSize:16]];
    label.textColor = [UIColor whiteColor];
    label.text = sectionTitle;
    [headerView addSubview:label];
    return headerView;
}

- (void)processSectionData
{
    NSArray *allDayArrays = @[self.sevenDays, self.fourteenDays, self.thirtyDays];
    // You won't use hard-coded strings here - use your sevenDaysSectionLabel, etc. variables instead
    NSArray *labelTitles = @[@"7 days", @"14 days", @"30 days"];
    NSMutableArray *mutableSectionModels = [NSMutableArray array];

    [allDayArrays enumerateObjectsUsingBlock:^(NSArray *array, NSUInteger index, BOOL *stop) {
        if ([array count] > 0) {
            CVSectionModel *sectionModel = [[CVSectionModel alloc] init];
            sectionModel.rowModels = array;
            sectionModel.sectionTitle = labelTitles[index];
            sectionModel.tag = index+1; // track this to enable re-ordering in the future
            [mutableSectionModels addObject:sectionModel];
        }
    }];

    // If Animating insertions / deletions will require something more elaborate
    self.sectionModels = [mutableSectionModels copy];
}

// Case 1:
// All three populated
- (void)testCase1
{
    self.sevenDays = @[@"sevendayitem1", @"sevendayitem2", @"sevendayitem3", @"sevendayitem4"];
    self.fourteenDays = @[@"14day item 1", @"14 day item 2"];
    self.thirtyDays = @[@"30 day item 1", @"30 day item 2", @"30 day item 3"];
}

// Case 2:
// self.fourteenDays is empty
- (void)testCase2
{
    self.sevenDays = @[@"sevendayitem1", @"sevendayitem2", @"sevendayitem3", @"sevendayitem4"];
    self.fourteenDays = @[];
    self.thirtyDays = @[@"30 day item 1", @"30 day item 2", @"30 day item 3"];
}

// Case 3:
// self.thirtydays is the only one
- (void)testCase3
{
    self.sevenDays = @[];
    self.fourteenDays = @[];
    self.thirtyDays = @[@"30 day item 1", @"30 day item 2", @"30 day item 3"];
}

@end