xcode 在 NSInteger 返回类型方法上返回 nil
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Return nil on NSInteger return type method
提问by ff10
I have the following UITableView DataSource method:
我有以下 UITableView DataSource 方法：
- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
On some items (i.e. section index titles) I just want to return "nothing", so that the table view won't jump to any section. I tried to return nil, but I get the "Return makes integer from pointer without a cast" - warning, since NSInteger is obviously not an object, just a typedef for 32/64 bit integers.
在某些项目（即部分索引标题）上，我只想返回“无”，以便表视图不会跳转到任何部分。我试图返回 nil，但我得到“返回从指针生成整数而不进行强制转换” - 警告，因为 NSInteger 显然不是一个对象，只是 32/64 位整数的 typedef。
How can I achieve no return / reaction on specific section index titles?
如何在特定部分索引标题上实现不返回/反应？
回答by Quinn Taylor
Returning nilis an error here since you're returning an integer primitive, not an object. (You're getting a cast warning because nilis actually a #definethat evaluates to ((void *)0), which is a null pointer, not an integer zero.) The best option for Objective-C code that interfaces with Cocoa is probably to use NSNotFound, a #definefor NSIntegerMaxwhich is used throughout Cocoa to signify that a given value does not exist in the receiver, etc. (Another option is to use -1, which is more common in C code. What works best depends on what the calling code expects and can handle.)
nil在这里返回是一个错误，因为您返回的是一个整数原语，而不是一个对象。（你得到的铸警告，因为nil实际上是一个#define计算结果为((void *)0)，这是一个空指针，而不是一个整数零）的Objective-C代码的最佳选择，与可可接口可能是使用NSNotFound，一个#define用于NSIntegerMax使用哪个在 Cocoa 中，用于表示接收器中不存在给定值等。（另一种选择是使用-1，这在 C 代码中更常见。什么效果最好取决于调用代码期望和可以处理的内容。）
Although NSNotFoundis a signed value, it's big enough that you're highly unlikely to run into a range issue. (NSIntegerMaxis approximately half of NSUIntegerMax, and very few people get remotely close to 2,147,483,647 objects — let alone twice that many — in 32-bit land. In 64-bit, forget about it; you'll run out of physical RAM in your machine long before you run out of integers for indexes.)
虽然NSNotFound是有符号值，但它足够大，您不太可能遇到范围问题。（NSIntegerMax大约是 的一半NSUIntegerMax，很少有人能远程接近 2,147,483,647 个对象——更不用说两倍——在 32 位领域。在 64 位中，忘记它；你的机器中的物理 RAM 会用完很长时间在用完索引的整数之前。）
Speaking of which, the Cocoa convention is to use NSUInteger(rather than NSInteger) for indexes. An unsigned integer cannot be negative, which offers somesanity protection on index values; among other things, it becomes easier to sort out accidental integer overflow/underflow. If this is a custom data source method (as it seems to be) I'd strongly suggest switching to using unsigned integers. (It may help to remember/realize that NSIntegerand NSUIntegeroccupy the same number of bytes, they just interpret the bits differently, so you won't "waste" any space by switching types.)
说到这里，Cocoa 约定是使用NSUInteger（而不是NSInteger）作为索引。无符号整数不能为负数，这为索引值提供了一些完整性保护；除此之外，整理意外的整数溢出/下溢变得更容易。如果这是一个自定义数据源方法（看起来是这样），我强烈建议改用无符号整数。（记住/意识到这一点NSInteger并NSUInteger占用相同数量的字节可能会有所帮助，它们只是以不同的方式解释位，因此您不会通过切换类型“浪费”任何空间。）
