[英]Arithmetic Operators and Key-Value Coding
是否可以使用Obj-C鍵值編碼進行算術運算? 我正在尋找這樣的東西:
[obj valueForKeyPath:@"(val1+val2)"]
還是必須實現一個手動添加兩個值的屬性?
無法使用KVC進行算術運算。
您可以使用字符串進行算術運算,然后將其傳遞給[obj valueforKeyPath:...]
作為:
NSString *val1=@"3";
NSString *val2=@"5";
NSString *formula = [NSString stringWithFormat:@"%@+%@",val1,val2];
NSExpression *exp = [NSExpression expressionWithFormat:formula];
NSNumber *resultForCustomFormula = [exp expressionValueWithObject:nil context:nil];
NSLog(@"%f", [resultForCustomFormula floatValue]);
我使用了AKV給出的NSExpression示例來創建此NSObject類別。
這擴展了valueForKeyPath:,因此它支持如下表達式:
[obj valueForKeyPath:@"(val1+val2)"];
或按示例:
[obj valueForKeyPath:@"@min.(val1+val2)"];
類別
#import <objc/runtime.h>
@implementation NSObject (KVCExtension)
#pragma mark - Initializing a Class
+ (void)load {
SEL valueForKeyPath = @selector(valueForKeyPath:);
SEL extendedValueForKeyPath = @selector(extendedValueForKeyPath:);
Method valueForKeyPathMethod = class_getInstanceMethod([self class], valueForKeyPath);
Method extendedValueForKeyPathMethod = class_getInstanceMethod([self class], extendedValueForKeyPath);
method_exchangeImplementations(valueForKeyPathMethod, extendedValueForKeyPathMethod);
}
#pragma mark - Key-Value Coding
- (id)extendedValueForKeyPath:(NSString *)keyPath {
/* NOTICE: +load exchanged this method with valueForKey: !!!
Thus calling extendedValueForKeyPath: now means we're calling the old valueForKeyPath: method and vice versa.
*/
if ([keyPath length] > 0 && [keyPath characterAtIndex:0] == '(') {
if ([self isKindOfClass:[NSArray class]]) {
NSMutableArray *results = [[NSMutableArray alloc] init];
for (id obj in (NSArray *)self)
[results addObject:[obj valueForKeyPath:keyPath]];
return [results copy];
} else {
NSRegularExpression *regExp = [NSRegularExpression regularExpressionWithPattern:@"[A-Za-z0-9_\\.]*"
options:0
error:nil];
NSMutableString *mKeyPath = [keyPath mutableCopy];
[regExp enumerateMatchesInString:mKeyPath options:0 range:NSMakeRange(0, [keyPath length]) usingBlock:^(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop) {
NSRange range = [[result resultByAdjustingRangesWithOffset:[mKeyPath length] - [keyPath length]] range];
if (range.length > 0) {
NSString *key = [mKeyPath substringWithRange:range];
NSString *val = [[self extendedValueForKeyPath:key] stringValue];
[mKeyPath replaceCharactersInRange:range withString:val];
}
}];
NSExpression *expression = [NSExpression expressionWithFormat:mKeyPath];
return [expression expressionValueWithObject:nil context:nil];
}
} else
return [self extendedValueForKeyPath:keyPath];
}
@end
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