動態映射objective-c的對象方法修改null 指標

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背景：目前iOS工程較多將json資料轉換成一個對象來儲存。假設這個對象有一個Attributes為NSString類型叫myName，這個Attributes一直是nil，建立這對象後忘記對它賦值。現在要通過一個函數來檢測他出來，再將他賦值為@“”；

另外，我不知道有多少個Attributes，只要是NSString類型而且Attributes是nil就賦值為@“”。

代碼如下：

//

//  GMCommonHelper.h

#import <Foundation/Foundation.h>

#import <objc/runtime.h>

@interface GMCommonHelper : NSObject

+(void)fixNilData:(id)kClass;

@end

//

//  GMCommonHelper.m

#import <AdSupport/AdSupport.h>

#import “GMCommonHelper.h"

@implementation GMCommonHelper

+(void)fixNilData:(id)kClass

{

    unsigned int propertyCount = 0;

    objc_property_t *properties = class_copyPropertyList([kClass class], &propertyCount);

    

    for (unsigned int i = 0; i < propertyCount; ++i) {

        objc_property_t property = properties[i];

        

        const char * name = property_getName(property);

        const char * attrs = property_getAttributes(property);

        NSString * utf8Name = [NSString stringWithUTF8String:name];

        NSString * utf8Attrs = [NSString stringWithUTF8String:attrs];

        id propertVal = [kClass valueForKey:utf8Name];

        if (!propertVal && [utf8Attrs hasPrefix:@"[email protected]\"NSString\""]) {

            [kClass setValue:@"" forKey:utf8Name];

        }

    }

    free(properties);

}

//———————————————————————

- (void)releaseProperties { unsigned int c = 0; objc_property_t *properties = class_copyPropertyList([self class], &c); for(unsigned int i = 0; i < c; i++) { objc_property_t property = properties[i]; NSString *propertyName = [NSString stringWithUTF8String:property_getName(property)]; NSString *propertyType = [NSString stringWithUTF8String:property_getAttributes(property)]; if([propertyType hasPrefix:@"[email protected]"] // is an object && [propertyType rangeOfString:@",R,"].location == NSNotFound // not readonly ) { [self setValue:nil forKey:propertyName]; NSLog(@"%@.%@ = %@", NSStringFromClass(cls), propertyName, [self valueForKey:propertyName]); } } free(properties);}

//———————————————————————

If you only care about classes you can use isKindOfClass:, but if you want to deal with scalars you are correct that you need to use property_getAttributes(), it returns a string that encodes the type information. Below is a basic function that demonstrates what you need to do. For examples of encoding strings, look here.

unsigned int outCount, i;objc_property_t *properties = class_copyPropertyList([object class], &outCount);for (i = 0; i < outCount; i++) {    objc_property_t property = properties[i];    char *property_name = property_getName(property);    char *property_type = property_getAttributes(property);    switch(property_type[1]) {      case ‘f‘ : //float        break;      case ‘s‘ : //short        break;      case ‘@‘ : //ObjC object        //Handle different clases in here        break;    }}

Obvviously you will need to add all the types and classes you need to handle to this, it uses the normal ObjC @encode type。