UISplitView，在设置代表时接收语义问题

Posted 2023-03-16

【中文标题】UISplitView，在设置代表时接收语义问题

【英文标题】：UISplitView, Receiving Semantic Issues in setting up delegates

【发布时间】：2012-11-16 19:43:45

【问题描述】：

我一直在关注 Big Nerd Ranch 的 ios 编程指南（第 3 版）来设置我的 Xcode 项目，该项目显示我公司产品的列表，然后是每个产品的详细视图。

我让应用程序按照我需要的方式流畅地运行，但是当我试图想象用户体验时，我开始遇到麻烦。为 iPad 添加 UISplitViewController 让我头疼欲裂，浪费了许多下午。

目前，我收到有关委托相关代码的语义问题的报告。一个在 DetailViewController.h 中，另一个在 ListViewController.m 中。

我会在发布之前总结一下我对这段代码的意图，但由于我缺乏经验，我可能会错过一些微妙之处：

AppDelegate 分配 UITableViewController（ListViewController 类）和 UIViewController（DetailViewController 类），然后检查是否有 iPad。如果是 iPad，它会使用两个视图的数组创建一个 UISplitViewController。否则它将 ListViewController 加载为主视图。

在我尝试在两个视图之间创建委托关系之前，应用程序已成功构建，但 iPad UISplitViewController 仅加载了一个空的详细视图。 iphone 加载 ListViewController，然后选择一行显示一个空的详细视图 (DetailViewController)。当您返回 TableView 并选择相同或另一个表格单元格时，正确的信息将加载到 DetailView 中。这让我相信 TableView 的初始实例没有正确传递选择，但返回它（重新分配它？）会纠正问题。我希望委托设置能解决这个问题。由于我无法使该部分正常工作，因此我无法测试该理论。我只是想我会提到它。

关于 UISplitViewController 问题和教程，我已经尽我所能（正确的关键字和搜索词使我无法理解）环顾四周，但它们都与我在项目中已经设置的内容大不相同，无论是应用程序的行为还是代码的整体结构。当我看起来如此接近时，我宁愿不必重新开始。

我打开了 BigNerdRanch 示例代码（它确实有效），正如我所说，唯一的区别似乎与我想要显示我的信息的方式有关。在这一点上，我需要一些帮助，以找出我做错了什么。

提前致谢！

AppDelegate.m：

#import "ProductFeedAppDelegate.h"
#import "ListViewController.h"
#import "DetailViewController.h"

@implementation ProductFeedAppDelegate

@synthesize window = _window;
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions


    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    ListViewController *lvc = [[ListViewController alloc] initWithStyle:UITableViewStylePlain];
    UINavigationController *masterNav = [[UINavigationController alloc] initWithRootViewController:lvc];

    DetailViewController *dvc = [[DetailViewController alloc] init];
    [lvc setDetailViewController:dvc];

    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) 


        UINavigationController *detailNav = [[UINavigationController alloc] initWithRootViewController:dvc];
        NSArray *vcs = [NSArray arrayWithObjects:masterNav, detailNav, nil];
        UISplitViewController *svc = [[UISplitViewController alloc] init];

        //set delegate
        [svc setDelegate:dvc];
        [svc setViewControllers:vcs];

        [[self window] setRootViewController:svc];

     else 

        [[self window] setRootViewController:masterNav];

    



    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;


//... trimmed out some template code to spare you
@end

` ListViewController.h：

    #import <Foundation/Foundation.h>
#import "ProductItemCell.h"
//#import "ItemStore.h"
#import "DetailViewController.h"

@class DetailViewController;

@class RSSChannel;

@interface ListViewController : UITableViewController 


    RSSChannel *channel;


@property (nonatomic, strong) DetailViewController *detailViewController;

-(void)fetchEntries;

@end

//A new protocol named ListViewControllerDelegate
@protocol ListViewControllerDelegate

//Classes that conform to this protocol must implement this method:
- (void)listViewController:(ListViewController *)lvc handleObject:(id)object;
@end

ListViewController.m:

#import "ListViewController.h"
#import "RSSChannel.h"
#import "RSSItem.h"
#import "DetailViewController.h"
#import "ContactViewController.h"
#import "FeedStore.h"

@implementation ListViewController
@synthesize detailViewController;

- (void)transferBarButtonToViewController:(UIViewController *)vc

    // Trimming Code

- (id)initWithStyle:(UITableViewStyle)style

    // Trimming Code


- (void)showInfo:(id)sender

    // Create the contact view controller
    ContactViewController *contactViewController = [[ContactViewController alloc] init];

    if ([self splitViewController]) 
        [self transferBarButtonToViewController:contactViewController];

        UINavigationController *nvc = [[UINavigationController alloc]
                                       initWithRootViewController:contactViewController];

        // Create an array with our nav controller and this new VC's nav controller
        NSArray *vcs = [NSArray arrayWithObjects:[self navigationController],
                        nvc,
                        nil];

        // Grab a pointer to the split view controller
        // and reset its view controllers array.
        [[self splitViewController] setViewControllers:vcs];

        // Make contact view controller the delegate of the split view controller
        [[self splitViewController] setDelegate:contactViewController];

        // If a row has been selected, deselect it so that a row
        // is not selected when viewing the info
        NSIndexPath *selectedRow = [[self tableView] indexPathForSelectedRow];
        if (selectedRow)
            [[self tableView] deselectRowAtIndexPath:selectedRow animated:YES];
     else 
        [[self navigationController] pushViewController:contactViewController
                                               animated:YES];
    

    // Give the VC the channel object through the protocol message
   // [channelViewController listViewController:self handleObject:channel];



- (void)viewDidLoad

    // Trimming Code



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

    return [[channel items] count];


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


    // Trimming Code



- (void)fetchEntries

    // Trimming Code


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


    if (![self splitViewController])
        [[self navigationController] pushViewController:detailViewController animated:YES];
    else 
        [self transferBarButtonToViewController:detailViewController];
        // We have to create a new navigation controller, as the old one
        // was only retained by the split view controller and is now gone
        UINavigationController *nav =
        [[UINavigationController alloc] initWithRootViewController:detailViewController];

        NSArray *vcs = [NSArray arrayWithObjects:[self navigationController],
                        nav,
                        nil];

        [[self splitViewController] setViewControllers:vcs];

        // Make the detail view controller the delegate of the split view controller
        [[self splitViewController] setDelegate:detailViewController];

    

    RSSItem *item = [[channel items] objectAtIndex:[indexPath row]];

     // Next line reports: No visible @interface for 'DetailViewController' declares the selector 'listViewController:handleObject:'
    [detailViewController listViewController:self handleObject:item]; 






@end

DetailViewController.h：

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import "ListViewController.h"

@class RSSItem;
@class Reachability;

@interface DetailViewController : UIViewController <ListViewControllerDelegate> // Cannot find protocol declaration for 'ListViewControllerDelegate' 

    __weak IBOutlet UILabel *nameField;
    __weak IBOutlet UITextView *descriptField;
    __weak IBOutlet UIImageView *imageView;
    __weak IBOutlet UITextView *introtextField;
    __weak IBOutlet UIButton *dsButton;
    __weak IBOutlet UIButton *aeButton;
    __weak IBOutlet UIButton *imButton;


-(BOOL)reachable;

@property (nonatomic, strong) RSSItem *item;
@property (nonatomic, strong) UIImage *productImage;

@end

DetailViewController.m：

#import "DetailViewController.h"
#import "RSSItem.h"
#import "RSSChannel.h"
#import "Reachability.h"


@interface DetailViewController ()

@end

@implementation DetailViewController

- (void)listViewController:(ListViewController *)lvc handleObject:(id)object

    //RSSItem *item = object; //This was in the example code but if left in the next line reported "Local declaration of 'item' hides instance variable"
    // Validate the RSSItem
    if (![item isKindOfClass:[RSSItem class]])
          return;

    [self setItem:item];
    [[self navigationItem] setTitle:[item name]];


    [nameField setText:[item name]];
    [descriptField setText:[item descript]];
    [introtextField setText:[item introtext]];


@synthesize item;

- (BOOL)reachable
    // Trimming Code

- (void)viewDidLoad

    [super viewDidLoad];
    [[self view] setBackgroundColor:[UIColor whiteColor]];


- (void)viewWillAppear:(BOOL)animated

    if (item)
        [super viewWillAppear:animated];

        [nameField setText:[item name]];
        [descriptField setText:[item descript]];
        [introtextField setText:[item introtext]];
        // Trimming Code (all the stuff that looks for this or that value and acts upon it)
      else 
        // The following appears in the log:
        NSLog(@"There's no item selected");
    





@end

【参考方案1】：

我认为你遇到了一个问题，编译器会因为有几个而感到困惑

#import "DetailViewController.h"

如果您从 ListViewController.h 中删除此导入并保留

@class DetailViewController;

那么我认为这将摆脱你的编译器问题。

您可能需要将< UISplitViewControllerDelegate > 添加到您的其他几个课程中。看起来您将它们设置为拆分视图上的委托，但未采用协议。

【讨论】：

谢谢，洛根！ （请注意，此答案是我发布给自己的答案的来源，其中逐行更改。）

【参考方案2】：

委托关系没有 100% 正确设置。这是解决此问题的方法。

在 ListViewController.m 中，添加了一个类扩展：

@interface ListViewController() <UISplitViewControllerDelegate>
@end

在 ListViewController.h 中，删除：

#import "DetailViewController.h"

在 DetailViewController.h 中，将行改为：

@interface DetailViewController : UIViewController <ListViewControllerDelegate, UISplitViewControllerDelegate>

在 ContactViewController.h 中，将行改为：

@interface ContactViewController : UIViewController <MFMailComposeViewControllerDelegate, UISplitViewControllerDelegate>

这些东西清除了所有错误。正如我在原始帖子中所希望的那样，这并没有纠正我的项目未传递给 detailViewController 的问题，因为该问题是在 DetailViewController.m 的 handleObject 语句中使用“item”而不是“object”的结果。