如何在切换 ViewController 时保留 UITableView 内容

Question

我在这里和其他网站上查看了许多代码示例，但我找不到与这种特定情况相关的示例，所以我想我会尝试询问。

我的应用程序使用启用了自动引用计数 (ARC) 的实用程序应用程序模板（主视图和反面视图）。

在另一面视图上，我有一个空的 UITableView，其中有一个导航栏，其中有一个“完成”按钮，可让您返回主视图和一个“添加”按钮。单击“添加”按钮会创建一个空行并激活 UIImagePicker。从 UIImagePicker 选择照片后，该照片将传递到新单元格的 imageView 中。

我的问题是，在向表中添加新行后，当我切换到主视图然后返回到翻转视图时，表再次为空。

我认为这与我如何将图像写入 NSMutableArray 有关。

如果有人知道如何防止 UITableView 在切换视图时被擦除，那就太棒了。

提前致谢，
斯蒂芬

AppDelegate.h

#import <UIKit/UIKit.h>

@class MainViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) MainViewController *mainViewController;

@end

AppDelegate.m

#import "AppDelegate.h"

#import "MainViewController.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize mainViewController = _mainViewController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.mainViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    self.window.rootViewController = self.mainViewController;
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    /*
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
     */
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
     */
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    /*
     Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
     */
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     */
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    /*
     Called when the application is about to terminate.
     Save data if appropriate.
     See also applicationDidEnterBackground:.
     */
}

@end

MainViewController.h

#import "FlipsideViewController.h"

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate>

- (IBAction)showInfo:(id)sender;

@end

MainViewController.m

#import "MainViewController.h"

@implementation MainViewController

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark - Flipside View

- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller
{
    [self dismissModalViewControllerAnimated:YES];
}

- (IBAction)showInfo:(id)sender
{    
    FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideViewController" bundle:nil];
    controller.delegate = self;
    controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:controller animated:YES];
}

@end

FlipsideViewController.h

#import <UIKit/UIKit.h>

@class FlipsideViewController;

@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

@interface FlipsideViewController : UIViewController <UIActionSheetDelegate, UIAlertViewDelegate, UIImagePickerControllerDelegate,UINavigationControllerDelegate>
{
NSMutableArray *dataArray;
IBOutlet UITableView *tableView;
IBOutlet UIBarButtonItem *addPhotoButton;
UITableViewCell *addedCell;
UIImage *image;
UIImagePickerController *imagePicker;
}

@property (nonatomic, strong) NSMutableArray *dataArray;
@property (nonatomic, strong) IBOutlet UITableView *tableView;
@property (nonatomic, strong) IBOutlet UIBarButtonItem *addPhotoButton;
@property (nonatomic, strong) UITableViewCell *addedCell;
@property (nonatomic, strong) UIImage *image;
@property (nonatomic, strong) UIImagePickerController *imagePicker;

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

- (IBAction)addPhoto:(id)sender;
- (IBAction)done:(id)sender;
@end

FlipsideViewController.m

#import "FlipsideViewController.h"
#import "MainViewController.h"

@implementation FlipsideViewController

@synthesize delegate = _delegate;
@synthesize dataArray, tableView, addPhotoButton, addedCell, image, imagePicker;

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
[super viewDidLoad];

self.dataArray = [[NSMutableArray alloc] init];
self.imagePicker = [[UIImagePickerController alloc] init];
self.imagePicker.allowsEditing = NO;    
self.imagePicker.delegate = self;   
self.imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
}

#pragma mark - UITableView delegate methods

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.dataArray.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *kCellID = @"cellID";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellID];
if (cell == nil)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:kCellID];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
cell.showsReorderControl = YES;
}

return cell;
}

- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark - Actions

- (IBAction)addPhoto:(id)sender
{
[self presentModalViewController:self.imagePicker animated:YES];
}


- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)img editingInfo:(NSDictionary *)editInfo {
// AppDelegate* appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
// appDelegate.pickerImage = img;

image = img;
[self dismissModalViewControllerAnimated:YES];

[self.tableView beginUpdates]; 
[self.dataArray addObject:@""];
NSArray *paths = [NSArray arrayWithObject:[NSIndexPath indexPathForRow:(self.dataArray.count - 1) inSection:0]];
[self.tableView insertRowsAtIndexPaths:paths withRowAnimation:NO];
[self.tableView endUpdates];

addedCell = [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:(self.dataArray.count - 1) inSection:0]];
addedCell.imageView.image = image;
[self.tableView reloadData];
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
NSUInteger row = [indexPath row];
[self.dataArray removeObjectAtIndex:row];
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}

- (IBAction)done:(id)sender
{
[self.delegate flipsideViewControllerDidFinish:self];
}
@end

Answer 1

你需要问自己问题，因为这是一个逻辑问题。

如何在 MainViewController 中创建 FlipsideViewController ？

您是否每次都创建一个新的，如果是或否，原因是什么？

您如何保持数据的活力？

至少有 3 或 4 种方式可能发生这种情况，主要是在我们的 MainViewController 中。

如果这些问题对您没有帮助，请发布 MainViewController 代码。

---

- (IBAction)showInfo:(id)sender  // this is trigger by IB
{    
//This is created each time
FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideViewController" bundle:nil];  
controller.delegate = self;
controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;

// HERE the 'controller' get retain by self and you don't have reference to it anymore,
[self presentModalViewController:controller animated:YES]; 

// So when the ModalView is finish your controller will be trash with all it's data
// If you don't hold on to something it will go away, thanks to ARC
}

问题与对象的生命周期有关

如果您认为用户会经常访问您的 FlipsideView，您可以创建它一次并将其保留在 MainView 的属性中。
如果没有，您可以将数组缓存在 MainView 中，并在创建后立即将其传递到 Flipside。
（在这两种情况下，如果您希望在应用程序启动之间保持持久性，则需要将可变数组保存到磁盘。如果将其保存到磁盘，它也可能是直接进入磁盘以获取信息的 Flipside）

我建议任何新的 Apple 程序员都需要学习和理解 retain 和 release 的内存管理。
因为 ARC 并不神奇，它代表自动引用计数。如果您了解 retain 和 release 的工作原理，您将更好地了解 ARC 的工作原理，并能够清楚地看到对象的生命周期。
（实际上 ARC 正在幕后执行 retain 和 release）

Answer 2

您需要将选择信息保存在独立于翻转视图的某个持久位置。当您返回到 Flipview 时，首先检查是否有保存的选择，然后根据该选择加载表格。