Question

我在setPropertyToFetch时收到错误。

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFArray initWithObjects:count:]: attempt to insert nil object at objects[0]'

代码：

 NSString *str;
str = [NSString stringWithFormat:@"Event%d", variable];
NSString *value  = [NSString stringWithFormat:@"values%d", vari];   
TermometrAppDelegate *app;
app = (TermometrAppDelegate *)[UIApplication sharedApplication].delegate;   
NSFetchRequest *fetchRequests = [[NSFetchRequest alloc] init];
NSEntityDescription *entit = [NSEntityDescription entityForName:str inManagedObjectContext:app.managedObjectContext];
[fetchRequests setEntity:entit] ;   
[fetchRequests setReturnsDistinctResults:YES];
    NSDictionary *entityProperties = [entit propertiesByName];
[fetchRequests setPropertiesToFetch :[NSArray arrayWithObject:[entityProperties objectForKey:value]]]; 
NSError *error;
fetchedObject = [app.managedObjectContext executeFetchRequest:fetchRequests error:&error];
NSManagedObject *fetched ;
printf("\n%d", [fetchedObject count]);
    if ([fetchedObject count]==0)
    { for (int h=0;h<31;h++){ NSManagedObject *Event = [NSEntityDescription insertNewObjectForEntityForName:str inManagedObjectContext:app.managedObjectContext];
    [Event setValue:[NSNumber numberWithInt:buf4[v+h]] forKey:value];  [app.managedObjectContext save:nil] ;}}
        else {fetched=[fetchedObject objectAtIndex:0];
            if([[fetched valueForKey:value] intValue]==0) {   
                for (int h=0;h<31;h++){  [[fetchedObject objectAtIndex:h] setValue:[NSNumber numberWithInt:buf4[v+h]] forKey:value];}
            }
            else{   printf("\n%d", buf4[v]);                
        for (int h=0;h<31;h++){     fetched=[fetchedObject objectAtIndex:h];
                int plus=[[fetched valueForKey:value] intValue];
                plus=(plus+buf4[v+h])/2;
        [[fetchedObject objectAtIndex:h] setValue:[NSNumber numberWithInt:plus] forKey:value];}
            }
        }

 [fetchRequests release];
[fetchedObject release];

**我忘了创建Enitity7 ... Entity64歇斯底里 - 在实体中获取属性的问题为期2周。
我认为你需要编写语言，每个单词 - 一个普通的文字 - 这意味着命令汇编程序。无论如何，你需要努力将编程语言作为纯数学和口语的语言。该语言与口语一样自由，客观编程将我们置于监狱**

Answer 1

最简单的解释是，value字符串的构造不正确，因此[entityProperties objectForKey:value]会返回nil值。

使用构造的实体和属性名称是一种危险的做法。这种结构非常非常容易出错并且导致细微且难以找到错误。为实体和属性提供唯一且有意义的名称并使用它们。

Answer 2

抛出异常是因为你试图将nil放入NSArray中。我看到你创建一个数组的唯一一次是：

[NSArray arrayWithObject:[entityProperties objectForKey:value]]

要检查的重点是：

[entityProperties objectForKey:value]

看看那是不是。如果那是零则然后向后工作以找出原因。

在核心数据中获取时出错

2 个答案: