如何解决仍然为零的委托

Posted 2023-03-13

【中文标题】如何解决仍然为零的委托

【英文标题】：How to solve a delegate that is still nil

【发布时间】：2012-04-23 06:02:47

【问题描述】：

我关心我的 4 个视图控制器。第一个是 CardWalletViewController，它是一个表格视图，由用户创建的卡片对象填充（卡片创建是可以的，所以我不会发布有关的代码）。现在，鉴于这个表格视图已经填充了卡片对象，一旦用户点击一个单元格，另一个名为 CardDetailsViewController 的视图控制器就会出现。这将显示卡的当前积分以及特权。请注意，当前点通过 UILabel 显示，并且特权是表格视图的单元格。此表视图的单元格值（特权）是静态类型的，来自 NSDictionary，然后存储在 NSArray 中（用于单元格的文本显示目的）。现在，当我点击一个福利时，PerksDetailsViewController 会出现。这包含显示 perk 名称和所需点数的 UILabels。这些 UILabels 值来自以前的 ViewController。此外，PerksDetailsVC 有一个名为兑换的按钮。单击该按钮后，我将进入另一个视图控制器 BarCodeViewController，它负责计算。

现在我关心的是如何通过选定的卡片，以及与选定的特权相对应的点数。我已经使用委托来执行此操作，但似乎我的委托对象没有被设置。

下面是我当前的代码。

CardWalletViewController.h

#import <UIKit/UIKit.h>
#import "Card.h"

@class CardWalletViewController;

@protocol CardWalletDelegate <NSObject>

-(void)cardWalletViewController: (CardWalletViewController *)sender
                withCurrentCard: (Card *) currentCard;

@end

@interface CardWalletViewController : UITableViewController 

@property (nonatomic, strong) NSMutableArray *myWallet;

@property (nonatomic, weak) id <CardWalletDelegate> delegate;

@end  

CardWalletViewController.m

#import "CardWalletViewController.h"
#import "AddCardViewController.h"
#import "Card.h"
#import "CardDetailsViewController.h"

@interface CardWalletViewController ()

@end

@implementation CardWalletViewController

@synthesize delegate = _delegate;

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

    NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = (UITableViewCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) 
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];

    
    Card *cardDummy = [self.myWallet objectAtIndex:indexPath.row]; //myWallet is an Array where the table cell's values come from
    cell.textLabel.text = cardDummy.name;
    cell.detailTextLabel.text = [NSString stringWithFormat:@"%@", cardDummy.points]; 

    return cell;


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

    //this method is responsible for showing the details of a selected card

    CardDetailsViewController *details = [self.storyboard instantiateViewControllerWithIdentifier:@"cardDetails"];


    Card *selectedCard = [self.myWallet objectAtIndex:indexPath.row]; // I want this selected card to be accessible until the user clicks another card or during end of program.

    details.myPoints = [NSString stringWithFormat:@"%@", selectedCard.points];

    [self.navigationController pushViewController:details animated:YES];


    [self.delegate cardWalletViewController:self withCurrentCard:selectedCard];

    //checking purposes
    if (!self.delegate) 
        NSLog(@"delegate is nil");
    

CardDetailsViewController.m

#import "CardDetailsViewController.h"
#import "PerksDetailsViewController.h"
#import "Card.h"

@interface CardDetailsViewController ()

@end

@implementation CardDetailsViewController

@synthesize pointsLabel = _pointsLabel;
@synthesize myPoints  = _myPoints;

@synthesize perks = _perks;
@synthesize datasource = _datasource;
@synthesize datasourcePoints = _datasourcePoints;

-(void)setupArray

    self.perks = [[NSMutableDictionary alloc] init];
    [self.perks setObject:@"200" forKey:@"10% Discount"];
    [self.perks setObject:@"100" forKey:@"250php Off"];

    self.datasource = [self.perks allKeys]; //contains perk's description
    self.datasourcePoints = [self.perks allValues]; //contains perk's required points


-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 

    return 2;


-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = (UITableViewCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (!cell) 
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    

 cell.textLabel.text = [self.datasource objectAtIndex:indexPath.row];
    cell.detailTextLabel.text = [self.datasourcePoints objectAtIndex:indexPath.row];

    return cell;


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

    PerksDetailsViewController *perksDetails = [self.storyboard instantiateViewControllerWithIdentifier:@"detailsOfMyPerks"];

    [self.navigationController pushViewController:perksDetails animated:YES];

    perksDetails.perkDetailsLabel.text = [self.datasource objectAtIndex:indexPath.row];
    perksDetails.pointsLabel.text = [self.perks objectForKey:perksDetails.perkDetailsLabel.text];


- (void)viewDidLoad


    //show the number of points of the selected Card
    self.pointsLabel.text = self.myPoints;

    [self setupArray];

    [super viewDidLoad];

PerksDetailsViewController.m

#import "PerksDetailsViewController.h"
#import "Card.h"
#import "CardWalletViewController.h"
#import "BarcodeViewController.h"

@interface PerksDetailsViewController ()

@end

@implementation PerksDetailsViewController

@synthesize pointsLabel = _pointsLabel;
@synthesize perkDetailsLabel = _perkDetailsLabel;
@synthesize perkDetailText = _perkDetailText;
@synthesize pointsText = _pointsText;
@synthesize delegate = _delegate;
@synthesize pointsRequired = _pointsRequired;


- (IBAction)redeemPressed:(id)sender 
    // get required points of a perk selected
    // cast the NSString value to an NSInteger

     NSNumberFormatter * f = [[NSNumberFormatter alloc] init];
     [f setNumberStyle:NSNumberFormatterDecimalStyle];

     self.pointsRequired = [f numberFromString: (self.pointsLabel.text)];

    NSLog(@"points required by the perk %@", self.pointsRequired);

    [self.delegate perksDetailsViewController:self didPassRequiredPoints:self.pointsRequired];

    if (!self.delegate)
        NSLog(@"delegate is nil");
    

PerksDetailsViewController.h

#import <UIKit/UIKit.h>
#import "BarcodeViewController.h"

@class PerksDetailsViewController;

@protocol PerksDetailsDelegate <NSObject>

- (void)perksDetailsViewController:(PerksDetailsViewController *)sender
             didPassRequiredPoints: (NSNumber *) requiredPoints;

@end

@interface PerksDetailsViewController : UIViewController

    NSString *perkDetailText;
    NSString *pointsText;
    IBOutlet UILabel *perkDetailsLabel;
    IBOutlet UILabel *pointsLabel;


@property (nonatomic, retain) IBOutlet UILabel *perkDetailsLabel, *pointsLabel;
@property (nonatomic, retain) NSString *perkDetailText, *pointsText;
@property (nonatomic, weak) NSNumber *pointsRequired;

@property (nonatomic, weak) id <PerksDetailsDelegate> delegate;

@end

现在这个 ViewController 实现了两个委托方法

BarCodeViewController.h

#import <UIKit/UIKit.h>

@interface BarcodeViewController : UIViewController 

@property (nonatomic, strong) NSNumber *myPoints;

@end

BarCodeViewController.m

  #import "BarcodeViewController.h"
    #import "CardWalletViewController.h"
    #import "Card.h"
    #import "PerksDetailsViewController.h"

    @interface BarcodeViewController () <CardWalletDelegate, PerksDetailsDelegate>

    @end

    @implementation BarcodeViewController

    @synthesize myPoints = _myPoints;
    - (void)perksDetailsViewController:(PerksDetailsViewController *)sender didPassRequiredPoints:(NSNumber *)requiredPoints 
    
        self.myPoints = requiredPoints;
    

    - (void)cardWalletViewController:(CardWalletViewController *)sender withCurrentCard:(Card *)currentCard 
    
        Card *myCurrentCard = currentCard;
        [myCurrentCard.pointsToDeduct addObject:self.myPoints];

        NSLog(@"contents :%@", [myCurrentCard.pointsToDeduct description]);
    

@end

【问题讨论】：

设置 PerksDetailsViewController 的委托属性的代码在哪里？

稍后会发布，敬请期待。

【参考方案1】：

首先，你的委托对象属性声明

@property (nonatomic, strong) id <PerksDetailsDelegate> delegate;

应该从 strong 更改为 weak，因为你的班级不拥有它。

其次，您永远不会为您的班级设置委托对象。这就是为什么它是nil 的原因。我的猜测是BarCodeViewController（您的PerksDetailsDelegate 协议实现类）应该是CardDetailsViewController 的实例变量，而您错过了将其设置为perksDetails 中perksDetails 对象的代表@。

编辑。

您应该在CardDetailsViewController 类中有一个BarCodeViewController 的实例（命名为bcvController，对于下面的示例代码）：

CardDetailsViewController.m

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

    PerksDetailsViewController *perksDetails = [self.storyboard instantiateViewControllerWithIdentifier:@"detailsOfMyPerks"];
    [perksDetails setDelegate:bcvController]; // bcvController should be created before this line
    [self.navigationController pushViewController:perksDetails animated:YES];

    perksDetails.perkDetailsLabel.text = [self.datasource objectAtIndex:indexPath.row];
    perksDetails.pointsLabel.text = [self.perks objectForKey:perksDetails.perkDetailsLabel.text];

编辑 2

BarCodeViewController.h

#import <UIKit/UIKit.h>
#import "CardWalletViewController.h"
#import "Card.h"
#import "PerksDetailsViewController.h"

@interface BarcodeViewController : UIViewController <CardWalletDelegate, PerksDetailsDelegate>

@property (nonatomic, strong) NSNumber *myPoints;

@end

BarCodeViewController.m

#import "BarcodeViewController.h"

//    @interface BarcodeViewController () 
//
//    @end

@implementation BarcodeViewController

@synthesize myPoints = _myPoints;
- (void)perksDetailsViewController:(PerksDetailsViewController *)sender didPassRequiredPoints:(NSNumber *)requiredPoints 

    self.myPoints = requiredPoints;


- (void)cardWalletViewController:(CardWalletViewController *)sender withCurrentCard:(Card *)currentCard 

    Card *myCurrentCard = currentCard;
    [myCurrentCard.pointsToDeduct addObject:self.myPoints];

    NSLog(@"contents :%@", [myCurrentCard.pointsToDeduct description]);


@end

编辑 3

如果你想显示一个 BarcodeViewController，你应该使用这个对象的 bcvController。

CardDetailsViewController.m

#import "CardDetailsViewController.h"
#import "PerksDetailsViewController.h"
#import "Card.h"

@implementation CardDetailsViewController

@synthesize pointsLabel = _pointsLabel;
@synthesize myPoints  = _myPoints;

@synthesize perks = _perks;
@synthesize datasource = _datasource;
@synthesize datasourcePoints = _datasourcePoints;
@synthesize bcvController = _bcvController; // new instance variable

// other functions removed for clarity

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

    PerksDetailsViewController *perksDetails = [self.storyboard instantiateViewControllerWithIdentifier:@"detailsOfMyPerks"];
    [perksDetails setDelegate:bcvController];
    [self.navigationController pushViewController:perksDetails animated:YES];

    perksDetails.perkDetailsLabel.text = [self.datasource objectAtIndex:indexPath.row];
    perksDetails.pointsLabel.text = [self.perks objectForKey:perksDetails.perkDetailsLabel.text];


- (void)viewDidLoad


    //show the number of points of the selected Card
    self.pointsLabel.text = self.myPoints;

    [self setupArray];

    [self setBcvController:[self.storyboard instantiateViewControllerWithIdentifier:@"myBarcodeVC"]]; // use setter to retain object properly

    [super viewDidLoad];

【讨论】：

谢谢！我已经把它从强变弱了。关于您的第二条建议，我该如何处理？在您最方便的时候给我一些样品。

我由此创建了 bcvController，BarcodeViewController *bcvController = [self.storyboard instantiateViewControllerWithIdentifier:@"myBarcodeVC"];这个好用吗？

我只是把它放在perksDetails的创建下。但是在这样做时，发生了一个错误，说“将'BarCodeViewController *_strong'发送到不兼容类型'id'的参数”

我的 BarCodeViewController.m 上有这个 @interface BarcodeViewController () @end 这个不正确吗？

好的，到此为止。利用它来设置属性 barCodeVC @property (nonatomic, strong) UIViewController *barCodeVC; 我猜现在正在设置委托对象。我已经编辑了使用if (self.delegate) NSLog(@"delegate is not nil"); 来检查它的方法。单击redeemPressed 后，现在会出现此NSLog 消息。即使它现在设置了委托对象，我现在在[perksDetails setDelegate: self.barCodeVC]; 行上收到一条警告，说“将 'UIViewController*' 发送到不兼容类型 'id' 的参数”