如何从Objective-C代码中删除一次性使用的类变量？

I'm writing some Objective-C code and I've frequently hit the situation where I have to use a class variable to store a value for one time use. After consuming it I no longer need it. To me, storing this value in a class variable seems like code smell. Really the value should be passed in as a parameter to the methods I'm using.

我正在编写一些Objective-C代码，而且我经常遇到必须使用类变量来存储一次使用值的情况。食用后我不再需要它了。对我来说，将这个值存储在类变量中似乎是代码味道。确实应该将值作为参数传递给我正在使用的方法。

I run across this usually when I'm consuming delegates. As an example, I have a UI with multiple buttons used to load and display a UIActionSheet when they're tapped. This action sheet contains a date picker which sets a value for a UILabel when the action sheet is dismissed.

当我消耗代表时，我经常遇到这种情况。作为一个例子，我有一个带有多个按钮的UI，用于在点击时加载和显示UIActionSheet。此操作表包含日期选择器，可在操作表解除时为UILabel设置值。

- (IBAction)setPurchaseDateTapped {
    self.activeField = purchaseDate;
    [self loadDatePickerActionSheet:@"Edit Purchase Date"];
}

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    self.activeField.text = value_from_UIActionSheet;
}

As you can see here, the actionSheet clickedButtonAtIndex callback doesn't allow me to pass the activeField so I have to use a class variable. It seems more correct to write this:

正如你在这里看到的，actionSheet clickedButtonAtIndex回调不允许我传递activeField所以我必须使用类变量。写这个似乎更正确：

- (void)actionSheet:(UIActionSheet *)actionSheet parameterValue:(id)parameter {
    parameter.text = value_from_UIActionSheet;
}

I believe(?) that I can subclass the UIActionSheet and UIActionSheet delegate and add the signatures that I require, but again this seems like more effort than it's worth.

我相信（？）我可以继承UIActionSheet和UIActionSheet委托并添加我需要的签名，但是这似乎更值得付出努力。

So my question is what is the best way to do what I'm trying to do?

所以我的问题是，做我想做的事情的最佳方法是什么？

I don't necessarily want to change the date picker/action sheet interface that I've created (although if there's a better pattern for setting multiple dates on a UIView while keeping the DatePicker out of the way, I'm all ears.)

我不一定想要更改我创建的日期选择器/操作表界面（尽管如果有一个更好的模式可以在UIView上设置多个日期同时保持DatePicker不碍事，我会全力以赴。）

3 个解决方案

#1

In this case, I think a simple subclass of UIActionSheet would be the way to go:

在这种情况下，我认为UIActionSheet的一个简单子类将是要走的路：

@interface SpecialActionSheet : UIActionSheet
{
    id parameter;
}
@property (assign) id parameter;
@end

@implementation SpecialActionSheet
@synthesize parameter;
@end

That should be enough, since all you want to do is have the actionSheet keep a parameter. Now, your code might look as follows:

这应该足够了，因为你想要做的就是让actionSheet保留一个参数。现在，您的代码可能如下所示：

- (void)loadDatePickerActionSheet:(NSString *)caption forField:(UITextField *)field {
    //...
    datePickerActionSheet.parameter = field;
}

- (IBAction)setPurchaseDateTapped {
    [self loadDatePickerActionSheet:@"Edit Purchase Date" forField:purchaseDate];
}

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    UITextField * field = ((SpecialActionSheet *)actionSheet).parameter;
    field.text = value_from_UIActionSheet;
}

#2

My usual approach in these situations is to use the tag property on UIAlertViews, and do a switch on it (it's an integer). It's not quite as nice as having a string or something to pass down, but if you've got multiple alerts, it's an easy way to disambiguate. For example:

在这些情况下我通常的做法是在UIAlertViews上使用tag属性，然后对它进行切换（它是一个整数）。它不像让字符串或其他东西传递下来那么好，但如果你有多个警报，这是一种消除歧义的简单方法。例如：

...
actionSheet.tag = [fields indexOfObject: self.activeField];
...        //fields is an NSArray of all the field objects I might have on the screen


- (void)actionSheet:(UIActionSheet *)actionSheet parameterValue:(id)parameter {
    [[field objectAtIndex: actionSheet.tag] setText: value_from_UIActionSheet];
}

#3

Another solution is to use associative storage.

另一种解决方案是使用关联存储。

UIActionSheet might already have it. You can test it by

UIActionSheet可能已经拥有它。你可以测试一下

[myActionSheet setValue:@"test value" forKey:@"testKey];
NSLog(@"%@",[myActionSheet valueForKey:@"testKey];

Associative storage is rather nifty if not overused.

如果不过度使用，关联存储相当漂亮。

#1