Question

我不断收到错误“由于未捕获的异常终止应用程序'NSInvalidArgumentException'，原因：'+ [MainViewController minimalFormInContext：]：无法识别的选择器发送到类” 从这行代码： NSLog（@“访问特定的矿山实体”）;

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Mine" inManagedObjectContext:managedObjectContext];   
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];   
NSError *error = nil;
[request setEntity:entity];  
NSPredicate *predicate;
NSPredicate *metalFilter;

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *region = [defaults stringForKey:@"mineArray"];

if([region isEqualToString:@"Butte & Plumas"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@)",@"Butte",@"Plumas"];
}
else if([region isEqualToString:@"Sutter, Yuba, & Sierra"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@) OR (county Contains %@)",@"Sutter",@"Yuba",@"Sierra"];
}
else if([region isEqualToString:@"Nevada & Placer"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@)",@"Nevada",@"Placer"];
}
else if([region isEqualToString:@"Sacramento & El Dorado"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@)",@"Sacramento",@"El Dorado"];
}
else if([region isEqualToString:@"San Joaquin, Amador, & Calaveras"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@) OR (county Contains%@)",@"San Joaquin",@"Amador", @"Calaveras"];
}
else if([region isEqualToString:@"Tuolumne & Stanislaus"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@)  OR (county Contains %@)",@"Tuolumne",@"Stanislaus"];
}
else if([region isEqualToString:@"Merced, Mariposa, & Madera"])
{
    predicate = [NSPredicate predicateWithFormat:@"(county Contains %@) OR (county Contains %@) OR (county Contains %@)",@"Merced",@"Mariposa",@"Madera"];
}

[request setPredicate:predicate];
mArray = [[NSMutableArray alloc] init];
mArray = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];

使用调试器，我已经缩小了错误：发生在：

mArray = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];

我该如何解决这个问题？

Answer 1

这可能是一个保留/释放错误。在XCode中执行“构建和分析”，并改进代码以删除所有警告。

以下是我注意到的事情：

mArray = [[NSMutableArray alloc] init];
mArray = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];

这两行非常糟糕。你的mArray是什么？ m代表member还是mutable？如果它是一个成员变量，你不应该像在

中那样只为它分配一个新数组

// mArray points to an array at this time, say X
mArray = [[NSMutableArray alloc] init];
// at this point, mArray points to an array Y created by alloc init. X is lost!

此外，如果您进一步指定mutableCopy，

mArray = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
// at this point, mArray points to an array Z created by mutableCopy. Y is lost, too!

请注意，在Objective-C中，您在源代码中看到的变量只是一个指针，而不是对象本身。如果为变量赋值，则不会使对象执行赋值操作，而只是将指针更改为指向不同的东西。

你有这些线条的事实表明你在其他各个地方都有类似的事情;任何一个最终都可能导致你遇到的错误。所以你需要逐个处理它们。祝好运！

另一点：当您准备变量predicate时，如果if与您列出的选项都不匹配，则predicate子句链将保留region。这是非常危险的，因为在Objective-C中，行

 NSPredicate* predicate;

不将predicate初始化为nil。所以有可能

[request setPredicate:predicate];

会将垃圾设置为predicate的{{1}}。你应该把它改成

requrest

无法将数据复制到可变数组

1 个答案: