Question

我正在尝试在iOS 7应用程序中实现Core Data（并且之前已成功完成）。但是，当我执行executeFetchRequest方法时，应用程序崩溃。下面添加了最相关的代码：

#import "JTHuntingSeasonDB.h"

@implementation JTHuntingSeasonDB

- (id)init {
    self = [super init];
    if (self) {
        NSFileManager *fileManager = [NSFileManager defaultManager];
        NSURL *documentsDirectory = [[fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] firstObject];

        NSString *documentName = @"JTHuntingDB";
        NSURL *url = [documentsDirectory URLByAppendingPathComponent:documentName];

        document = [[UIManagedDocument alloc] initWithFileURL:url];


        BOOL fileExists  = [[NSFileManager defaultManager] fileExistsAtPath:[url path]];

        if (fileExists) {
            [document openWithCompletionHandler:^(BOOL success) {
                if (success) {
                    NSLog(@"Document opened successfully");
                    self.allSpecies = [self getSpecies];
                    self.speciesToday = [self getSpeciesToday];
                } else NSLog(@"Failed to open document");
            }];
        } else {
            [document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
                if (success)  {
                    NSLog(@"Document created successfully");
                    self.allSpecies = [self getSpecies];
                    self.speciesToday = [self getSpeciesToday];
                }  else NSLog(@"Failed to create document, path: %@", url);
            }];
        }
    }

    return self;
}

#pragma mark - Core Data

- (NSArray *)getSpecies {
    if (document.documentState == UIDocumentStateNormal) {
        context = document.managedObjectContext;

        NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
        NSString *country = [defaults stringForKey:@"Country"];
        NSString *subregion = [defaults stringForKey:@"Subregion"];

        NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"HuntingDates"];
        NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedStandardCompare:)];
        request.fetchBatchSize = 150;
        request.fetchLimit = 150;
        request.sortDescriptors = @[sortDescriptor];

        if (subregion.length > 0) {
            request.predicate = [NSPredicate predicateWithFormat:@"(country IN %@) AND (subregion IN %@)", country, subregion];
        } else {
            request.predicate = [NSPredicate predicateWithFormat:@"country IN %@", country];
        }

        NSError *error;
        return [context executeFetchRequest:request error:&error];
    }

    return nil;
}

该行

return [context executeFetchRequest:request error:&error];

导致应用崩溃。这是我到目前为止所做的和发现的：

模拟器：删除了应用并重置了内容和设置
Xcode：Clean（构建文件夹）
“context”不是nil
NSLog打印出“文档已创建/已成功打开”
当应用程序崩溃时，控制台中仅打印“lldb”

修改按照Wain的建议，我关闭异常断点，得到一条更具描述性的错误消息，说谓词无效。通过用CONTAINS替换谓词中的IN并更改变量“country”以使其不再返回nil来解决问题。

Answer 1

我猜这是你的谓词，因为IN是一个集合运算符，但是你传递字符串（应该是数组/集）。

如果您正在使用字符串，则应在谓词中使用CONTAINS。

Answer 2

假设CoreData持久存储位于文档中，您将需要使用UIManagedDocument

executefetchrequest导致崩溃

2 个答案: