iOS Programming Camera 2

iOS Programming Camera  2 

1.1 Creating BNRImageStore

The image store will fetch and cache the images as they are needed. It will also be able to flush the cache if the device runs low on memory.

 

Create a new NSObject subclass called BNRImageStore. Open BNRImageStore.h and create its interface:

 

#import <Foundation/Foundation.h> @interface BNRImageStore : NSObject + (instancetype)sharedStore;

- (void)setImage:(UIImage *)image forKey:(NSString *)key; - (UIImage *)imageForKey:(NSString *)key;
- (void)deleteImageForKey:(NSString *)key;

@end

 

In BNRImageStore.m, add a class extension to declare a property to hang onto the images. @interface BNRImageStore ()

@property (nonatomic, strong) NSMutableDictionary *dictionary; @end
@implementation BNRImageStore

 

Like the BNRItemStore, the BNRImageStore needs to be a singleton. In BNRImageStore.m, write the following code to ensure BNRImageStore's singleton status.

@implementation BNRImageStore

+ (instancetype)sharedStore

{
static BNRImageStore *sharedStore = nil;

if (!sharedStore) {

sharedStore = [[self alloc] initPrivate]; }

return sharedStore; }

// No one should call init - (instancetype)init

{
@throw [NSException exceptionWithName:@"Singleton"

return nil; }

reason:@"Use +[BNRImageStore sharedStore]" userInfo:nil];

// Secret designated initializer - (instancetype)initPrivate

{
self = [super init];

if (self) {

_dictionary = [[NSMutableDictionary alloc] init]; }

return self; }

-  (void)setImage:(UIImage *)image forKey:(NSString *)key
{
[self.dictionary setObject:image forKey:key];
} 

-  (UIImage *)imageForKey:(NSString *)key
{
return [self.dictionary objectForKey:key];
} 

-  (void)deleteImageForKey:(NSString *)key
{
if (!key) {
return; }
[self.dictionary removeObjectForKey:key]; } 

 

1.2 Creating and Using Keys

When an image is added to the store, it will be put into a dictionary under a unique key, and the associated BNRItem object will be given that key. When the BNRDetailViewController wants an image from the store, it will ask its item for the key and search the dictionary for the image. Add a property to BNRItem.h to store the key.

@property (nonatomic, copy) NSString *itemKey;

 

The image keys need to be unique in order for your dictionary to work.

爲了讓你的dictionary 工做，你必須讓image key 是獨特的。

While there are many ways to hack together a unique string, you are going to use the Cocoa Touch mechanism for creating universally unique identifiers (UUIDs), also known as globally unique identifiers (GUIDs).

有許多方式組成一個獨特的string，你能夠使用cocoa touch mechanism 來建立universally unique  identifiers（UUIDs）,也就是globally unique identifiers (GUIDs). 

Objects of type NSUUID represent a UUID and are generated using the time, a counter, and a hardware identifier, which is usually the MAC address of the WiFi card.

類型爲NSUUID 的對象表明了一個UUID 。它由time，counter,a hardware identifier ,which is usually the mac address of the  wifi card .

When represented as a string, UUIDs look something like this:

4A73B5D2-A6F4-4B40-9F82-EA1E34C1DC04

 

#import "BNRImageStore.h"

 

// Create an NSUUID object - and get its string representation NSUUID *uuid = [[NSUUID alloc] init];
NSString *key = [uuid UUIDString];

_itemKey = key;

 

 

// Store the image in the BNRImageStore for this key [[BNRImageStore sharedStore] setImage:image

forKey:self.item.itemKey];

 

Therefore, the key is a persistent way of referring to an image.

一個key 是指向一個image 的持久化方式。

1.3 Wrapping up BNRImageStore

you need to teach BNRDetailViewController how to grab the image for the selected BNRItem and place it in its imageView.

你應該告訴BNRDetailViewController怎樣獲取image 對於選定的BNRItem，並把它放到它的imageView上。

 

The BNRDetailViewController's view will appear at two times: when the user taps a row in BNRItemsViewController and when the UIImagePickerController is dismissed. In both of these situations, the imageView should be populated with the image of the BNRItem being displayed.

NSString *imageKey = self.item.imageKey;

// Get the image for its image key from the image store

UIImage *imageToDisplay = [[BNRImageStore sharedStore] imageForKey:imageKey];

// Use that image to put on the screen in the imageView

self.imageView.image = imageToDisplay;

 

If there is no image associated with the item, then imageForKey: will return nil. When the image is nil, the UIImageView will not display an image.

若是沒有與該項鍊接的image，那麼imageForKey 將會返回nil。當image 是nil時，UIImageView將不展現一個image。

1.4 Dismissing the Keyboard

 

When the keyboard appears on the screen in the item detail view, it obscures BNRDetailViewController's imageView. This is annoying when you are trying to see an image, so you are going to implement the delegate method textFieldShouldReturn: to have the text field resign its first responder status to dismiss the keyboard when the return key is tapped.

因此你將要實現委託 方法textFieldShouldReturn 來讓text field resign 它的first responder status 來取消keyboard 當return 建按下時候。 

- (BOOL)textFieldShouldReturn:(UITextField *)textField

{
[textField resignFirstResponder];

return YES; }

 

It would be stylish to also dismiss the keyboard if the user taps anywhere else on BNRDetailViewController's view. You can dismiss the keyboard by sending the view the message endEditing:, which will cause the text field (as a subview of the view) to resign as first responder.

你能夠經過給view發 信息endEditing來解除keyboard,這將會致使text field  resign as first responder .

You have seen how classes like UIButton can send an action message to a target when tapped. Buttons inherit this target-action behavior from their superclass, UIControl.

Buttons 繼承這個tareget action  行自 UIControl。

You are going to change the view of BNRDetailViewController from an instance of UIView to an instance of UIControl so that it can handle touch events.

 

In BNRDetailViewController.xib, select the main View object. Open the identity inspector and change the view's class to UIControl

- (IBAction)backgroundTapped:(id)sender

{
[self.view endEditing:YES];

}