如何使用objective-c从CloudKit中的资产字段中检索图像

Posted 2023-03-08

【中文标题】如何使用objective-c从CloudKit中的资产字段中检索图像

【英文标题】：How to retrieve an image from an asset field in CloudKit using objective-c

【发布时间】：2016-02-07 15:44:25

【问题描述】：

我在 CloudKit 中有一个记录类型。它存储一个字符串字段和一个资产字段。使用仪表板，我将图像上传到资产字段。

我可以检索字符串字段。我现在需要检索资产字段的内容并使用objective-c 将其存储到图像中。有人可以帮忙吗？

我正在尝试在表格视图中显示记录类型。我有一个名为 TJKCategoriesViewController 的类，它继承自 UIViewController。

我在 TJKCategoriesViewController 类的 viewDidLoad 方法中有这段代码：

// get all categories
_jokeCategories = [[NSMutableArray alloc] init];
CKDatabase *jokePublicDatabase = [[CKContainer containerWithIdentifier:JOKE_CONTAINER] publicCloudDatabase];
NSPredicate *predicateCategory = [NSPredicate predicateWithFormat:@"CategoryName != %@", CATEGORY_TO_REMOVE_OTHER];
CKQuery *queryCategory = [[CKQuery alloc] initWithRecordType:CATEGORY_RECORD_TYPE predicate:predicateCategory];
NSSortDescriptor *sortCategory = [[NSSortDescriptor alloc] initWithKey:CATEGORY_FIELD_NAME ascending:YES];
queryCategory.sortDescriptors = [NSArray arrayWithObjects:sortCategory, nil];
[jokePublicDatabase performQuery:queryCategory inZoneWithID:nil completionHandler:^(NSArray<CKRecord*>* results, NSError * error)
 
     if (!error)
      
         // add all categories to array
         for (CKRecord* jokeCategory in results)
         
             TJKCategories *categories = [TJKCategories initWithCategory:[jokeCategory valueForKey:CATEGORY_FIELD_NAME] categoryImage:[jokeCategory valueForKey:@"CategoryImage"]];
             [_jokeCategories addObject:categories];
         


         NSLog(@"Categories = %@",_jokeCategories);

         // setup table
         [self setupTableContents];
     
     else
     
         // display alert message and pop the view controller from the stack
         GHSAlerts *alert = [[GHSAlerts alloc] initWithViewController:self];
         errorActionBlock errorBlock = ^void(UIAlertAction *action) [self closeCategories:self];;
         [alert displayErrorMessage:@"Oops!" errorMessage:@"The joke categories failed to load. This screen will close. Just try again!" errorAction:errorBlock];
     
 ];

这是“setupTableContents”方法

// setup the array that will hold the table's contents
-(void)setupTableContents
   
    // store to property and reload the table contents
    dispatch_async(dispatch_get_main_queue(), ^
        [self.categoriesTableView reloadData];
    );

TJKCategories 是一个将两个字段存储在记录类型中的类。这是 TJKCategories.h 文件：

#import <UIKit/UIKit.h>

@interface TJKCategories : NSObject

#pragma Properties

@property (nonatomic, copy) UIImage *categoryImage;
@property (nonatomic, copy) NSString *categoryName;

#pragma Initializers
+(instancetype)initWithCategory:(NSString *)categoryName
                  categoryImage:(UIImage *)categoryImage;


-(instancetype)initWithCategory:(NSString *)categoryName
                  categoryImage:(UIImage *)categoryImage;

@end

这是 TJKCategories.m 文件：

// designated initializer
-(instancetype)initWithCategory:(NSString *)categoryName categoryImage:(UIImage *)categoryImage

    self = [super init];

    if (self)
    
        self.categoryImage = categoryImage;
        self.categoryName = categoryName;
    

    return self;


// class level initializer
+(instancetype)initWithCategory:(NSString *)categoryName categoryImage:(UIImage *)categoryImage

    TJKCategories *category = [[self alloc]initWithCategory:categoryName categoryImage:categoryImage];
    return category;


// override default initializer
-(instancetype)init

    return [self initWithCategory:@"" categoryImage:nil];

在我使用的 viewDidLoad 方法中：[jokePublicDatabase performQuery:queryCategory inZoneWithID:nil completionHandler:^(NSArray* results, NSError * error)

检索记录类型的结果。然后我循环遍历结果数组，我可以检索字符串“CATEGORY_FOR_NAME”（这是“CategoryName”的常量，但是当我尝试检索图像“CategoryImage”的字段时，我得到“无法识别的选择器发送到实例" 错误。

如果你想知道常量后面的名字是什么，这里是我的联系人文件：

// declare constants
extern NSString *const DEFAULT_CATEGORY;
extern NSString *const JOKE_CONTAINER;
extern NSString *const CATEGORY_RECORD_TYPE;
extern NSString *const CATEGORY_FIELD_NAME;
extern NSString *const CATEGORY_TO_REMOVE_OTHER;
extern NSString *const CATEGORY_TO_REMOVE_RANDOM;
extern NSString *const JOKE_RECORD_TYPE;
extern NSString *const JOKE_DESCR;
extern NSString *const JOKE_SUBMITTED_BY;
extern NSString *const JOKE_TITLE;

// assign values to constants
NSString *const DEFAULT_CATEGORY = @"None";
NSString *const JOKE_CONTAINER = @"iCloud.com.glennseplowitz.Jokes";
NSString *const CATEGORY_RECORD_TYPE = @"Categories";
NSString *const CATEGORY_FIELD_NAME = @"CategoryName";
NSString *const CATEGORY_TO_REMOVE_OTHER = @"Other";
NSString *const CATEGORY_TO_REMOVE_RANDOM = @"Random";
NSString *const JOKE_RECORD_TYPE = @"Jokes";
NSString *const JOKE_DESCR = @"jokeDescr";
NSString *const JOKE_SUBMITTED_BY = @"jokeSubmittedBy";
NSString *const JOKE_TITLE = @"jokeTitle";

所以我要做的是从记录类型中检索资产类型“CategoryImage”并将其存储到 UIImage。但就像我说的那样，它给了我错误“无法识别的选择器发送到实例”，因为我相信它不能直接将资产字段转换为 UIImage 字段。

谢谢， 格伦

【问题讨论】：

用一些相关代码更新您的问题。展示你尝试过的东西。说明您遇到的问题以及您具体需要哪些帮助。

嗨 rmaddy，在我看来确实加载方法我有这个代码

嗨 rmaddy，感谢您告诉我拼写所有代码。通过这样做，它让我重新思考事情。所以你确实帮助了我。

【参考方案1】：

想通了！我将 TJKCategories 类更改为接受 CKAsset 而不是 UIImage。然后我将 CKAsset 转换为 UIImage。

这是 TJKCategories.h 文件：

#import <UIKit/UIKit.h>
#import <CloudKit/CloudKit.h>

@interface TJKCategories : NSObject

#pragma Properties

@property (nonatomic, copy) UIImage *categoryImage;
@property (nonatomic, copy) NSString *categoryName;

#pragma Initializers
+(instancetype)initWithCategory:(NSString *)categoryName
                  categoryImage:(CKAsset *)categoryImageAsset;


-(instancetype)initWithCategory:(NSString *)categoryName
                  categoryImage:(CKAsset *)categoryImageAsset;


@end

这是 TJKCategories.m 文件：

#import "TJKCategories.h"

@interface TJKCategories()

#pragma Properities
@property (nonatomic, strong) CKAsset *categoryImageAsset;

@end

@implementation TJKCategories

#pragma initializers

// designated initializer
-(instancetype)initWithCategory:(NSString *)categoryName categoryImage:(CKAsset *)categoryImageAsset

    self = [super init];

    if (self)
    
        self.categoryImageAsset = categoryImageAsset;
        self.categoryName = categoryName;
        UIImage *image = [[UIImage alloc] initWithContentsOfFile:self.categoryImageAsset.fileURL.path];
        self.categoryImage = image;       
    

    return self;


// class level initializer
+(instancetype)initWithCategory:(NSString *)categoryName categoryImage:(CKAsset *)categoryImageAsset

    TJKCategories *category = [[self alloc]initWithCategory:categoryName categoryImage:categoryImageAsset];
    return category;


// override default initializer
-(instancetype)init

    return [self initWithCategory:@"" categoryImage:nil];

我也改了行：

TJKCategories *categories = [TJKCategories initWithCategory:[jokeCategory valueForKey:CATEGORY_FIELD_NAME] categoryImage:[jokeCategory **objectForKey**:@"CategoryImage"]];

到

TJKCategories *categories = [TJKCategories initWithCategory:[jokeCategory valueForKey:CATEGORY_FIELD_NAME] categoryImage:[jokeCategory **valueForKey**:@"CategoryImage"]];

注意 CategoryImage 现在使用 valueForKey 而不是 objectForKey。