Question

查看了从不同类访问NSMuatableArray的所有主题，并尝试了所有答案，但仍然无法从不同的类访问MutableArray。

我的代码：

ViewController.m

@interface ViewController () <UITableViewDataSource, UITableViewDelegate>

@property (strong, nonatomic) NSArray *printProductImages;
@property (strong, nonatomic) NSArray *printProductNames;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tableView.delegate = self;
    self.tableView.dataSource = self;

    _printProductImages = [NSArray arrayWithObjects:@"demo_1.jpg", @"demo_2.jpg", @"demo_3.jpg",nil];
    _printProductNames = [NSArray arrayWithObjects:@"text", @"text", nil];
}


- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    AnotherViewController *anotherVC = [[AnotherViewController alloc] init];

    switch (indexPath.row) {
        case 0:

           [anotherVC.array1 removeAllObjects]; // does not work and no error
           [anotherVC.array1 addObjectsFromArray:_printProductImages]; // does not work and no error

           [anotherVC.array2 removeAllObjects]; // does not work and no error
           [anotherVC.array2 addObjectsFromArray:_printProductNames]; // does not work and no error

           [self performSegueWithIdentifier:@"AnotherViewController" sender:self];

            NSLog(@"~~Row: 1");
            break;
        case 1:
            NSLog(@"~~Row: 2");
            break;
        default:
            break;
    }

AnotherViewController.h

@interface AnotherViewController: UIViewController

@property (strong, nonatomic) NSMutableArray *array1;
@property (strong, nonatomic) NSMutableArray *array2;

@end

AnotherViewController.m

@implementation AnotherViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.tableView.delegate = self;
    self.tableView.dataSource = self;
    _array1 = [NSMutableArray arrayWithObjects:@"demo_3.jpg", @"demo_4", @"demo_1.jpg", @"demo_2.jpg",nil]; // I want to delete these objects and load new objects to this array
    _array2 = [NSMutableArray arrayWithObjects:@"BIG", @"SMALL", @"MEDIUM", @"SUPER GOOD", nil]; // I want to delete these objects and load new objects to this array

Answer 1

您创建的anotherVC未添加到视图层次结构中，因此其view属性未被访问，这意味着viewDidLoad中的AnotherViewController在修改anotherVC.array1之前尚未调用，此时anotherVC.array1为零。

尝试下面的代码，我通过anotherVC.view手动访问其视图，这可能不是一个好主意，但我会告诉你机制。

AnotherViewController *anotherVC = [[AnotherViewController alloc] init];
anotherVC.view; // access its view property so viewDidLoad will be called
switch (indexPath.row) {
    case 0:

       [anotherVC.array1 removeAllObjects];
       [anotherVC.array1 addObjectsFromArray:_printProductImages];
       [anotherVC.array2 removeAllObjects];
       [anotherVC.array2 addObjectsFromArray:_printProductNames];

       [self performSegueWithIdentifier:@"SquarePhotos" sender:self];

        NSLog(@"~~Row: 1");
        break;
    case 1:
        NSLog(@"~~Row: 2");
        break;
    default:
        break;
}

顺便说一下，你最好在AnotherViewController的init方法中创建NSMutableArray。

- (id) init 
{
    self = [super init]  ;
    if (self) {
        _array1 = [NSMutableArray arrayWithObjects:@"Some Objects",nil]; 
        _array2 = [NSMutableArray arrayWithObjects:@"Some Objects", nil]; 
    }
    return self; 
}

Answer 2

这一行是你的大问题，

 AnotherViewController *anotherVC = [[AnotherViewController alloc] init];

这将创建一个AnotherViewController的实例，它与您正在进行的操作无关 - 它永远不会出现在屏幕上，并且会在didSelectRowAtIndexPath：完成后立即释放。你应该得到一个你正在准备的实例的引用，你在prepareForSegue中得到了（根本没有必要实现didSelectRowAtIndexPath：）。

我不清楚，为什么在AnotherViewController中创建2个数组，然后在切换到该控制器时删除其中的所有对象。除非您在控制器的init方法中创建数组，否则无论如何都无法工作，因为在prepareForSegue时，目标视图控制器的视图尚未加载。如果那是你想要做的，你可以这样做（这假设你直接从单元格到另一个ViewController），

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(UITableViewCell *)sender {
    NSIndexPath *indexPath = [self.tableView indexPathForCell:sender];
    if ([segue.identifier isEqualToString:@"AnotherViewController"]) {
        AnotherViewController *anotherVC = segue.destinationViewController;
        switch (indexPath.row) {
            case 0:
               [anotherVC.array1 removeAllObjects];
               [anotherVC.array1 addObjectsFromArray:_printProductImages];
               [anotherVC.array2 removeAllObjects];
               [anotherVC.array2 addObjectsFromArray:_printProductNames];

               NSLog(@"~~Row: 1");
               break;
            case 1:
                NSLog(@"~~Row: 2");
                break;
            default:
                break;
        }
   }
}

在AnotherViewController中，将2个数组（需要是可变数组）的创建移动到initWithCoder：方法

Answer 3

This is where we set viewcontroller ID
为UI中的AnotherViewController设置任何viewcontrollerID [与图像中的storyboardID相同]

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
       AnotherViewController *anotherVC = [storyboard instantiateViewControllerWithIdentifier:@"Viewcontroller ID"];

    anotherVC.array1=[[NSmutablearray alloc]init];

然后尝试

switch (indexPath.row) {
        case 0:

           [anotherVC.array1 removeAllObjects]; // does not work
           [anotherVC.array1 addObjectsFromArray:_printProductImages];

           [anotherVC.array2 removeAllObjects]; // does not work
           [anotherVC.array2 addObjectsFromArray:_printProductNames];

           [self performSegueWithIdentifier:@"SquarePhotos" sender:self];

            NSLog(@"~~Row: 1");
            break;
        case 1:
            NSLog(@"~~Row: 2");
            break;
        default:
            break;
    }

无法从不同的类访问NSMuatableArray

3 个答案: