Question

我有一个tableView来自NSString的{{1}}值。我将单元配置为检查/取消选中单元格。这非常有效。

我正在尝试配置单元格，因此单击单元格中的一个标签会触发到另一个视图控制器的segue。我配置了标签并在我想要做segue的地方扔了一个日志声明，一切正常。当我添加segue时，没有编译器错误，但它在运行时崩溃并出现以下错误：

NSFetchedResultsController

我相当肯定我做了一件令人吃惊的事情，但是我很难过。我欢迎提出建议。

MyCustomCell.h：

2015-05-31 08:09:04.656 MyApp[17682:1240919] -[UIViewController selectedItemPhoto:]: unrecognized selector sent to instance 0x7fa42b65d4e0
2015-05-31 08:09:04.694 MyApp[17682:1240919] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIViewController selectedItemPhoto:]: unrecognized selector sent to instance 0x7fa42b65d4e0'

FirstVC.m方法：

@property (strong, nonatomic) IBOutlet UILabel *itemDescription; @property (strong, nonatomic) IBOutlet UILabel *itemGroup; @property (strong, nonatomic) IBOutlet UIImageView *itemImage;方法

cellForRowAtIndexPath

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { // implement custom cell MyCustomCell *customCell = [tableView dequeueReusableCellWithIdentifier:@"customCell" forIndexPath:indexPath]; // Get a hold of myManagedObject from FRC MyNSManagedObject *myObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; // Configures 1st label to look like a hyperlink customCell.itemDescription.text = myObject.itemDescription; customCell.itemDescription.textColor = [UIColor blueColor]; customCell.itemDescription.userInteractionEnabled = YES; // Enables gesture and sets demoObject to pass along via the segue called from labelTap UITapGestureRecognizer *labelTapGesture = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(labelTap)]; [customCell.itemDescription addGestureRecognizer:labelTapGesture]; self.demoObject = myObject; // Configures 2nd label within customCell customCell.itemGroup.text = myObject.itemGroup; // add image to cell, already imported into Images.xcassets NSString *imageName = [NSString stringWithFormat:@"%@-1.jpg", myObject.photo]; customCell.imageView.image = [UIImage imageNamed:imageName]; // The following code ensures random checkmarks don't appear when the user scrolls. if ([self.selectedObjects containsObject:[self.fetchedResultsController objectAtIndexPath:indexPath]]) { customCell.accessoryType = UITableViewCellAccessoryCheckmark; } else { customCell.accessoryType = UITableViewCellAccessoryNone; } return customCell; }方法

didSelectRowAtIndexPath

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { self.selectedObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; // Set the checkmark accessory for the selected row. if ([tableView cellForRowAtIndexPath:indexPath].accessoryType == UITableViewCellAccessoryNone) { [[tableView cellForRowAtIndexPath:indexPath] setAccessoryType:UITableViewCellAccessoryCheckmark]; [self.selectedObjects addObject:self.selectedObject]; [tableView deselectRowAtIndexPath:indexPath animated:YES]; } else { [[tableView cellForRowAtIndexPath:indexPath] setAccessoryType:UITableViewCellAccessoryNone]; [self.selectedObjects removeObject:self.selectedObject]; [tableView deselectRowAtIndexPath:indexPath animated:YES]; } // Enables save button if there are items in the selectedObjects array if (self.selectedObjects.count > 0) { [self.saveButton setEnabled:YES]; } else { [self.saveButton setEnabled:NO]; } }方法

labelTap

- (void) labelTap { // The "hyperlink" effect I'm trying to achieve works without the segue NSLog(@"itemDescription tapped"); [self performSegueWithIdentifier:@"mySegue" sender:nil]; }方法

prepareForSegue

SecondViewController.h属性

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([[segue identifier] isEqualToString:@"mySegue"] && self.demoObject != nil) {
        // This line returns a value...
        NSLog(@"self.demoObject = %@", self.demoObject.itemDescription);
        // ...but it crashes here when it tries to set on the destinationViewController
        SecondViewController *destinationViewController = [segue destinationViewController];
        destinationViewController.selectedItemPhoto = self.demoObject.photo;
        destinationViewController.selectedItemTitle = self.demoObject.itemDescription;
    }
}

Answer 1

从错误看，您似乎没有设置第二个视图控制器的类。它似乎是UIViewController，应该是SecondViewController。

在故事板中选择第二个视图控制器并将其类设置为SecondViewController。

另一个建议是，在Objective C中，你应该在投射对象之前使用内省。所以在你的代码中我会添加：

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([[segue identifier] isEqualToString:@"mySegue"] && self.demoObject != nil) {
        // This line returns a value...
        NSLog(@"self.demoObject = %@", self.demoObject.itemDescription);
        // ...but it crashes here when it tries to set on the destinationViewController
        if ([[segue destinationViewController] isKindOfClass:[SecondViewController class]]) {
            SecondViewController *destinationViewController = (SecondViewController *)[segue destinationViewController];
            destinationViewController.selectedItemPhoto = self.demoObject.photo;
            destinationViewController.selectedItemTitle = self.demoObject.itemDescription;
        }
    }
}

通过这种方式，segue不会发生，但应用程序不会崩溃。

Answer 2

我明白了！我有三个问题（两个被捆绑在一起）：

问题1： Juan Catalan指出我没有设置SecondViewController的故事板

问题2： Yuchen＆amp; luk2302提出了我如何执行segue的问题。

问题3：我不需要prepareForSegue

这就是我的所作所为：

1：我删除了prepareForSegue。

2：我删除了故事板segue。

2：我更改了labelTap方法，为labelTapGesture添加参数

- (void) labelTap:(UITapGestureRecognizer *)sender {
    NSLog(@"stretchDescription tapped");

    CGPoint location = [sender locationInView:self.view];

    if (CGRectContainsPoint([self.view convertRect:self.tableView.frame fromView:self.tableView.superview], location)) {
        CGPoint locationInTableview = [self.tableView convertPoint:location fromCoordinateSpace:self.view];
        NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:locationInTableview];
        if (indexPath) {
            self.demoObject = [self.fetchedResultsController objectAtIndexPath:indexPath];
            DisplayStretchViewController *destinationViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"SecondVC"];

            // Set properties on destinationVC
            destinationViewController.itemPhoto = self.demoObject.photo;
            destinationViewController.itemTitle = self.demoObject.stretchDescription;
            [self.navigationController pushViewController:destinationViewController animated:YES];
        }
    }
}

我还发现这篇文章非常有帮助： UILabel with Gesture Recognizer inside UITableViewCell blocks didSelectRowAtIndexPath

感谢大家的投入！

将NSManagedObject属性的字符串值传递给新视图控制器

2 个答案: