objective-c - 覆盖 setter 方法并获取信息

Question

我有一个 setter 方法（setMinimumNumberOfSides），我想在使用合成后覆盖它。在其中，我对实例变量施加了约束，以确保 int 在一定范围内。

稍后在自定义初始化方法中，我设置了另一个实例变量 (numberOfSides)，但我需要确保 minimumNumberOfSides 和 maximumNumberOfSides 在界限内正确设置。我尝试将 setter 上的返回值更改为 BOOL，所以如果它成功/失败，我可以传回 YES 或 NO，但这会产生冲突的方法，我猜是因为我正在使用 synthesize 并覆盖 setter。

如何轻松获取信息以检查 setter 是否被调用并成功返回？

-(void)setNumberOfSides:(int)sides
{
    if ((sides < maximumNumberOfSides) && (sides > minimumNumberOfSides))
    {
        numberOfSides = sides;  
    }
    else
        NSLog (@"Invalid number of sides: %d is outside the constraints allowed", sides);


}

-(void)setMinimumNumberOfSides:(int)minimum 
{
    if (minimum > 2)
        minimumNumberOfSides = minimum;

}

-(void)setMaximumNumberOfSides:(int)maximum 
{
    if (maximum <= 12)
        maximumNumberOfSides = maximum;

}

-(id)initWithNumberOfSides:(int)sides minimumNumberOfSides:(int)min maximumNumberOfSides:(int)max 
{
    if (self = [super init])
    {
        self.minimumNumberOfSides = min;
        self.maximumNumberOfSides = max;

        self.numberOfSides = sides;
    }
    return self;
}

Answer 1

You don't have to synthesize numberOfSides if you're planning on implementing the getter and setter. Without @synthesize numberOfSides you can return a BOOL if you choose. You'll need to declare the getter/setter in your interface accordingly.

BTW, another approach would be to use the synthesized getter/setter and add a separate method -(BOOL)isNumberOfSidesValid which performs this check.

Answer 2

In a situation like this, you may be better off using a simple call to assert(), or throwing an exception.

The choice will depend on how you see this class being used. If it will be part of a library, and you expect other developers to frequently supply incorrect values for minimumNumberOfSides or maximumNumberOfSides, you should probably throw a proper exception.

A word of warning, though. If you expect the users of your application to frequently supply incorrect values, then an exception is a bad idea. Exception handling in Objective-C is an expensive operation. If these checks are in place for the sake of the user, you should perform input validation, and report errors to the user in a much more friendly manner.

edit: Here is some quick sample code:

-(void)setMinimumNumberOfSides:(int)minimum
{
    if (minimum <= 2)
    {
        [NSException raise:@"invalid minimumNumberOfSides value"
                    format:@"value of %d is too low (must be > 2)", minimum];
    }

    minimumNumberOfSides = minimum;
}

edit: Here is another SO question that goes into detail about exception handling in Objective-C.