当没有可用于tableView的数据时显示自定义标签 [英] Show custom label when no data available for tableView

问题描述

相关应用可让用户将商品标记为收藏。当用户没有保存收藏夹时，我想通知他们这个事实（大多数我讨厌空白tableView的想法）。

The app in question has an ability for users to mark items as favourite. When the user has no favourites saved, I'd like to notify them of the fact (mostly I hate the idea of a blank tableView).

当用户没有标记为收藏的项目时，我的 numberOfRowsInSection 为零。我想设置cell.textLabel.text = @你没有收藏夹，但是当没有表的项目时，不会调用cellForRowAtIndexPath 。

My numberOfRowsInSection is zero when there are no items the user has marked as favourite. I'd like to set cell.textLabel.text = @"You have no favourites" but when there are no items for the table cellForRowAtIndexPath is not called.

我可以测试 numberOfRowsInSection 在遇到0时给出结果然后在中测试1行cellForRowAtIndexPath 然后插入自定义文本，但如果他们只有一个收藏夹会怎样？

I could test numberOfRowsInSection to give a result when it encounters a 0 and then test for 1 row in cellForRowAtIndexPath and then insert the custom text but then what if they only have one favourite?

更新

我尝试实现上面的想法，并在下面推荐，但也许我做得不对，可能是因为它是一个fetchedResultsController，其中委托方法在发生更改时更新表。

I tried implementing the idea I had above, and recommended below, but perhaps I'm not doing it right, probably due to the fact that it's a fetchedResultsController with the delegate methods to update the table when a change occurs.

当我在表格中只有一个单元格时删除单元格时出现此错误：

I get this error when I delete the cell when there is but one cell in the table:

***断言失败 - [UITableView _endCellAnimationsWithContext：]，/ SourceCache / UIKit_Sim / UIKit-1447.6.4 / UITableView.m：976
严重的应用程序错误。在调用-controllerDidChangeContent：期间，从NSFetchedResultsController的委托中捕获到异常。无效更新：第0节中的行数无效。更新（1）后现有部分中包含的行数必须等于更新前该部分中包含的行数（1），加上或减去数字从该部分插入或删除的行数（插入0，删除1）。 with userInfo（null）

当第一个地方没有要显示的单元格时，它会崩溃：

and when there are no cells to be displayed in the first place it crashes with:

***由于未捕获的异常'NSRangeException'终止应用程序，原因：'*** - [_ PFBatchFaultingArray objectAtIndex：]：索引（0）超出边界（0） '

以下是相关代码：

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    // Return the number of rows in the section.
    id <NSFetchedResultsSectionInfo> sectionInfo = [[_fetchedResultsController sections] objectAtIndex:section];

    if ([sectionInfo numberOfObjects]==0) {
        return 1;
    } else {
        return [sectionInfo numberOfObjects];
    }
} 

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {

if ([[_fetchedResultsController sections] objectAtIndex:0]==0) {
    cell.textLabel.text = @"You have no favorites";
} else {
    Shows *show = [_fetchedResultsController objectAtIndexPath:indexPath];

    cell.textLabel.text = show.ShowsToSerials.serialName;
    cell.detailTextLabel.text = [NSString stringWithFormat:@"%@", show.showTitle];
}
}

推荐答案

1在我自己的iOS应用程序中，我创建了一个带有UILabel的子视图，说没有结果
当numberOfSectionsInTableView为零时，我将子视图添加到tableview。当它是！=零时，我将其删除。
这当然要求将子视图作为保留对象保留在内存中，以便您可以将其删除。

1) In my own iOS apps, I create a subview with a UILabel in it, saying "No Results" When numberOfSectionsInTableView is zero, I add the subview to the tableview. When it is != zero, I remove it. This of course requires maintaining the subview in memory as a retained object, so that you can remove it.

2）如果要将一个单元格设为你有点提到：
当numberOfSectionsInTableView为零时，返回1.然后，在numberOfRowsInSection中也返回1。
在cellForRowAtIndexPath中，检查numberOfSectionsInTableView和numberOfRowsInSection，如果它们应该为零（毕竟你返回1），则显示任何消息。

2) If you want to make one cell as you somewhat mentioned: When numberOfSectionsInTableView is zero, return 1. Then, in numberOfRowsInSection return 1 as well. In cellForRowAtIndexPath, check both numberOfSectionsInTableView and numberOfRowsInSection, and if they SHOULD be zero (after all you returned 1), then display whatever message.

解决方案1需要维护一个变量来保存子视图，但代码更短更清晰，我相信CPU密集度更低（不会导致任何重大性能问题）。

Solution 1 requires maintaining a variable to hold the subview, but is shorter and cleaner code, and I believe is less CPU intensive (not that either will cause any significant performance issues).

编辑以包含代码：
它实际上与我想的有点不同，但基本相同。
这里显然有些东西需要改变以适应你的代码和品味。

Edit to include code: It was actually a little different than I thought, but basically the same. There are obviously things in here that are to be changed to fit your code and taste.

（确保声明 UIView * nomatchesView; in .h）

(Make sure to declare UIView *nomatchesView; in .h)

- (void)viewDidLoad{

        nomatchesView = [[UIView alloc] initWithFrame:self.view.frame];
        nomatchesView.backgroundColor = [UIColor clearColor];

        UILabel *matchesLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,0,320,320)];
        matchesLabel.font = [UIFont boldSystemFontOfSize:18];
        matchesLabel.minimumFontSize = 12.0f;
        matchesLabel.numberOfLines = 1;
        matchesLabel.lineBreakMode = UILineBreakModeWordWrap;
        matchesLabel.shadowColor = [UIColor lightTextColor];
        matchesLabel.textColor = [UIColor darkGrayColor];
        matchesLabel.shadowOffset = CGSizeMake(0, 1);
        matchesLabel.backgroundColor = [UIColor clearColor];
        matchesLabel.textAlignment =  UITextAlignmentCenter;

        //Here is the text for when there are no results
        matchesLabel.text = @"No Matches";


        nomatchesView.hidden = YES;
        [nomatchesView addSubview:matchesLabel];
        [self.tableView insertSubview:nomatchesView belowSubview:self.tableView];
    }



    - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
    {
        //If there is no table data, unhide the "No matches" view
        if([data count] == 0 ){
        nomatchesView.hidden = NO;
        } else {
        nomatchesView.hidden = YES;
        }

        return [data count];
    }

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