iOS实战之后台返回数据为空造成程序崩溃

((AFJSONResponseSerializer *)manager.responseSerializer).removesKeysWithNullValues = YES;

#import <objc/runtime.h>
#import <Foundation/Foundation.h>
static NSString *dataKey = @"key";

@interface NSNull ()

@property (strong, nonatomic) NSMutableDictionary *data;

@end

@implementation NSNull (Safe)

#pragma mark - LifeCycle

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
@synchronized([self class])
{
NSString *selString = NSStringFromSelector(selector);
NSMethodSignature *signature = nil;

NSRange range = [selString rangeOfString:@"set"];

if (range.length) {
signature = [NSMethodSignature signatureWithObjCTypes:"v@:@"];
} else {
signature = [NSMethodSignature signatureWithObjCTypes:"@@:"];
}

return signature;
}
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
NSString *key = NSStringFromSelector(invocation.selector);

NSRange range = [key rangeOfString:@"set"];

if (range.length) {
key = [[key substringFromIndex:3] lowercaseString];
id obj;
[invocation getArgument:&obj atIndex:2];
[self.data setObject:obj forKey:key];
} else {
id obj = self.data[key];
[invocation setReturnValue:&obj];
}

}

#pragma mark - Private

- (NSMutableDictionary *)data {
NSMutableDictionary *data = objc_getAssociatedObject(self, &dataKey);

while (!data) {
objc_setAssociatedObject(self, &dataKey, [NSMutableDictionary dictionary], OBJC_ASSOCIATION_COPY_NONATOMIC);
data = objc_getAssociatedObject(self, &dataKey);
}

return data;
}

@end