Question

我有两个视图控制器，一个传递对象，另一个按照预期传递给另一个。但是当我尝试传递字符串时，某种程度上会发生一些事情，因为在另一个ViewController上它始终返回为（null）。我在这里遗失了什么？

ViewController one.h

@class ViewControllerTwo;

@interface ViewControllerOne : UIViewController{

    ViewControllerTwo* playboard;

@property(nonatomic, retain) ViewControllerTwo* playBoard;

@end

ViewController One

playBoard = [[ViewControllerTwo alloc] init];    
        [playBoard setQuickPlayFilters:[[NSMutableArray alloc] init]];
        [playboard setChallenge:[[NSString alloc] init]];


passToPlayboard = [[NSString alloc] initWithString:@"one"];                    
                    filters = [[NSMutableArray alloc] initWithObjects:
                               [NSNumber numberWithInt:5],
                               [NSNumber numberWithInt:1],
                               [NSNumber numberWithInt:1],
                               [NSNumber numberWithInt:2],
                               [NSNumber numberWithInt:9],
                               [NSNumber numberWithInt:0],
                               [NSNumber numberWithInt:0],
                               [NSNumber numberWithInt:8], nil];

  [playBoard setQuickPlayFilters:[filters mutableCopy]];
      [playboard setChallenge:[NSString stringWithString:passToPlayboard]];

Touch_TestingAppDelegate* appDelegate = [[UIApplication sharedApplication] delegate];
      [appDelegate.navController pushViewController:playBoard animated:YES];

ViewController Two.h

#import <UIKit/UIKit.h>

@interface ViewControllerTwo : UIViewController {
    NSString* challenge;
NSMutableArray* quickPlayFilters;
}

@property(nonatomic, retain) NSString* challenge;
@property(nonatomic, retain) NSMutableArray* quickPlayFilters;

@end

ViewController Two.m

- (void)viewDidLoad{
    [super viewDidLoad];

    cover = [[CoverView alloc] initWithFrame:CGRectMake(140.0f, 80.0f, 620.0f, 610.0f) andRemaningTiles:[quickPlayFilters lastObject]];
    cover.backgroundColor = [UIColor clearColor];
    [self.view addSubview:cover];

    NSLog(@"Quick Play : %@", quickPlayFilters);
    NSLog(@"Challenge from Load : %@", challenge);


    [[self cover] setFilters:[quickPlayFilters mutableCopy]];

    timerDisplay = [[TimerDisplay alloc] 
                    initWithFrame:CGRectMake(813.f, 120.f, 181.f, 162.f) 
                    andTimeCycle:[quickPlayFilters objectAtIndex:0] 
                    andNumberOfRows:[quickPlayFilters objectAtIndex:6]]; 
}

当我在quickPlayFilters中寻找playBoard时，我可以立即找到它们。但是我不能为challenge字符串返回除null之外的任何内容。请帮忙。

Answer 1

主要问题是ViewControllerTwo.h中的拼写错误。 playboard iVar全部为小写，但属性为camelcase（playBoard）。这导致您的班级有两个iVars（playboard和playBoard）。修复拼写错误，以便所有内容都为playBoard，并且可以正常运行。

我的初步答案留待参考，因为我仍然建议您按照我的建议清理代码。我修改了代码以在所有实例中使用playBoard。

=原始答案

如果没有在ViewControllerTwo.m中查看您的代码，则无法回答这个问题。确保challenge的属性定义为：

@property (nonatomic, copy)  NSString * challenge;

如果您有自定义设置器，请确保它正在执行正确的分配ala：

- (void)setChallenge:(NSString *)newChallenge
{
    if (![challenge isEqualToString:newChallenge]) {
        challenge = [newChallenge copy];
        // whatever else you need to do
    }
}

你正在创建一堆你并不真正需要的对象。你上面的代码可能是：

playBoard = [[ViewControllerOne alloc] init];    
passToPlayBoard = [[NSString alloc] initWithString:@"one"];
filters = [[NSMutableArray alloc] initWithObjects:
    [NSNumber numberWithInt:5],
    [NSNumber numberWithInt:1],
    [NSNumber numberWithInt:1],
    [NSNumber numberWithInt:2],
    [NSNumber numberWithInt:9],
    [NSNumber numberWithInt:0],
    [NSNumber numberWithInt:0],
    [NSNumber numberWithInt:8], nil];

[playBoard setQuickPlayFilters:filters];
[playBoard setChallenge:passToPlayBoard];

Touch_TestingAppDelegate* appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate.navController pushViewController:playBoard animated:YES];

注意：上面的代码假设您的项目使用ARC。如果没有，您将必须适当地释放对象。

编辑：发现实际问题。添加到这个答案的顶部。

Answer 2

在setChallenge方法中，请保留您的对象值.. like。

（void）setChallenge：（NSString *）newChallenge {
```
challenge = [newChallenge retain];
```
}

无法在ViewControllers之间传递NSString，而其他对象可以

2 个答案: