cellForRowAtIndexPath 返回 null 但确实需要类似的方法

Question

我的UITableViewController 中有一个UITableView（很明显，哈哈），但我需要在- (void)viewWillAppear:(BOOL)animated 方法内的给定索引处获取一个单元格。

现在，我的单元格是静态的，我在界面构建器中创建它们。如果我打电话给

UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:previously_selected_cell.integerValue inSection:0]];

它为单元格返回 null。我在 1 个部分中只有 3 个静态单元格。我尝试了第 0 节和第 1 节，都返回 null。

目前我已经删除了- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 方法，因为如果我添加它，它将清除我所有静态单元格的UITableView。

我可以在- (void)viewWillAppear:(BOOL)animated 中调用一个方法来返回给定索引处的单元格吗？

提前致谢！

编辑：我检查了this stackoverflow question，但我使用的是没有 cellForRowAtIndexPath 的静态单元格，所以这个问题没有帮助。 :(

EDIT2：我正在尝试在视图加载时设置单元格的附件类型。但仅限于某个单元格，该单元格是用户在退出应用之前选择的那个单元格。

#import "AutoSyncSettings.h"
#import "CDFetchController.h"


@implementation AutoSyncSettings

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    CDFetchController *cdfc = [[CDFetchController alloc] init];
    NSFetchedResultsController *results = [cdfc getFetchedResultsControllerWithEntityName:@"SETTINGS"];
    NSArray *objects = [results fetchedObjects];
    NSNumber *sync_setting;

    if(objects.count > 0)
    {     
        NSManagedObject *object = [objects objectAtIndex:0];
        sync_setting = [object valueForKey:@"wifi_setting"];

        NSLog(@"(Settings)sync_setting: %@",sync_setting);
    NSLog(@"(Settings)sync_setting int value: %i",sync_setting.integerValue);
    NSLog(@"(Settings)TableView: %@",self.tableView);

//cell is null, even after this.
    UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:wifi_settings.integerValue inSection:0]];
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
//cell is still null. WHY OH WHY? :(

        objects = nil;
    }

    cdfc = nil;
    results = nil;
    objects = nil;
    sync_setting = nil;

    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    return NO;
}

- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
    return NO;
}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    for (int i = 0; i < [tableView numberOfRowsInSection:indexPath.section]; i++)
    {
        if([[tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:indexPath.section]] accessoryType] == UITableViewCellAccessoryCheckmark)
        {
            [tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:indexPath.section]].accessoryType = UITableViewCellAccessoryNone;
        }
    }

    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    cell.accessoryType = UITableViewCellAccessoryCheckmark;

    CDFetchController *cdfc = [[CDFetchController alloc] init];
    NSFetchedResultsController *results = [cdfc getFetchedResultsControllerWithEntityName:@"SETTINGS"];
    NSManagedObjectContext *context = [results managedObjectContext];
    NSArray *objects = [results fetchedObjects];

    if(objects.count > 0)
    {

        NSManagedObject *object = [objects objectAtIndex:0];

        NSNumber *sync_setting = [NSNumber numberWithInt:indexPath.row];
        [object setValue:sync_setting forKey:@"sync_interval"];
        [object setValue:[NSNumber numberWithInt:0] forKey:@"id"];

        [ErrorHandler saveMoc:context];
    }
    else
    {
        //INSERT NEW OBJECT
        NSManagedObject *object = [NSEntityDescription insertNewObjectForEntityForName:@"SETTINGS" inManagedObjectContext:context];

        NSNumber *sync_setting = [NSNumber numberWithInt:indexPath.row];
        [object setValue:sync_setting forKey:@"sync_interval"];
        [object setValue:[NSNumber numberWithInt:0] forKey:@"id"];

        [ErrorHandler saveMoc:context];
    }
}

@end

Answer 1

我有一个项目正是这样做的，而且效果很好。但是，除非您在尝试以这种方式访问​​单元格之前调用 [super viewWillAppear:animated]，否则它不起作用。

基本实现可能会从情节提要加载到单元格中。

Answer 2

我想在之前选择的单元格中添加一个复选标记附件， 即使应用程序，previous_selected_cell 变量也会被存储 退出/崩溃

要走的路是控制你的 cellForRowAtIndexPath 实现中的 indexPath 并在它等于 previous_selected_cell.integerValue 时采取行动：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{ 
    // usual cache lookup, allocation of the cell, etc
    if (indexPath.row == previously_selected_cell.integerValue) {
        // add checkbox here
    } else {
        // remove checkbox
    }
}